Add support for regex-based target type/pattern specific variables

This is in addition to the already supported path-based target type/pattern
specific variables. For example:

hxx{*}:     x = y  # path-based
hxx{~/.*/}: x = y  # regex-based

14 files changed, 710 insertions, 261 deletions

diff --git a/libbuild2/dump.cxx b/libbuild2/dump.cxx
index bc44b24..23d430e 100644
--- a/libbuild2/dump.cxx
+++ b/libbuild2/dump.cxx
@@ -147,6 +147,9 @@ namespace build2
                   const variable_type_map& vtm,
                   const scope& s)
   {
+    using pattern = variable_pattern_map::pattern;
+    using pattern_type = variable_pattern_map::pattern_type;
+
     for (const auto& vt: vtm)
     {
       const target_type& t (vt.first);
@@ -154,7 +157,7 @@ namespace build2
 
       for (const auto& vp: vpm)
       {
-        const string p (vp.first);
+        const pattern& pat (vp.first);
         const variable_map& vars (vp.second);
 
         os << endl
@@ -163,7 +166,10 @@ namespace build2
         if (t != target::static_type)
           os << t.name << '{';
 
-        os << p;
+        if (pat.type == pattern_type::regex_pattern)
+          os << '~';
+
+        os << pat.text;
 
         if (t != target::static_type)
           os << '}';
diff --git a/libbuild2/lexer.cxx b/libbuild2/lexer.cxx
index 0b6f96d..f445d4b 100644
--- a/libbuild2/lexer.cxx
+++ b/libbuild2/lexer.cxx
@@ -674,18 +674,15 @@ namespace build2
     bool qcomp (false);
     bool qfirst (false);
 
-    auto append = [&lexeme, &m, &qcomp, &qfirst] (char c)
+    auto append = [&lexeme, &m, &qcomp, &qfirst] (char c, bool escaped = false)
     {
-      if (m == lexer_mode::double_quoted)
-      {
-        if (lexeme.empty ()) // First character.
+      if (lexeme.empty () && (escaped || m == lexer_mode::double_quoted))
           qfirst = true;
-      }
-      else
-      {
-        if (qcomp) // An unquoted character after a quoted fragment.
-          qcomp = false;
-      }
+
+      // An unquoted character after a quoted fragment.
+      //
+      if (m != lexer_mode::double_quoted && qcomp)
+        qcomp = false;
 
       lexeme += c;
     };
@@ -716,7 +713,7 @@ namespace build2
             fail (p) << "unterminated escape sequence";
 
           if (p != '\n') // Ignore if line continuation.
-            append (p);
+            append (p, true);
 
           continue;
         }
diff --git a/libbuild2/name.cxx b/libbuild2/name.cxx
index 6a33a63..1081b5c 100644
--- a/libbuild2/name.cxx
+++ b/libbuild2/name.cxx
@@ -82,8 +82,21 @@ namespace build2
   ostream&
   to_stream (ostream& os, const name& n, bool quote, char pair, bool escape)
   {
-    auto write_string = [quote, pair, escape, &os](const string& v, bool pat)
+    using pattern_type = name::pattern_type;
+
+    auto write_string = [&os, quote, pair, escape] (
+      const string& v,
+      optional<pattern_type> pat = nullopt,
+      bool curly = false)
     {
+      // Special characters, path pattern characters, and regex pattern
+      // characters. The latter only need to be quoted in the first position
+      // and if followed by a non-alphanumeric delimiter. If that's the only
+      // special character, then we handle it with escaping rather than
+      // quoting (see the parsing logic for rationale). Additionally, we
+      // escape leading `+` in the curly braces which is also recognized as a
+      // path pattern.
+      //
       char sc[] = {
         '{', '}', '[', ']', '$', '(', ')', // Token endings.
         ' ', '\t', '\n', '#',              // Spaces.
@@ -93,9 +106,24 @@ namespace build2
         '\0'};
 
       char pc[] = {
-        '*', '?',                          // Wildcard characters.
+        '*', '?',                          // Path wildcard characters.
         '\0'};
 
+      auto rc = [] (const string& v)
+      {
+        return (v[0] == '~' || v[0] == '^') && v[1] != '\0' && !alnum (v[1]);
+      };
+
+      if (pat)
+      {
+        switch (*pat)
+        {
+        case pattern_type::path:                          break;
+        case pattern_type::regex_pattern:      os << '~'; break;
+        case pattern_type::regex_substitution: os << '^'; break;
+        }
+      }
+
       if (quote && v.find ('\'') != string::npos)
       {
         // Quote the string with the double quotes rather than with the single
@@ -115,6 +143,11 @@ namespace build2
         if (escape) os << '\\';
         os << '"';
       }
+      //
+      // Note that a regex pattern does not need to worry about special path
+      // pattern character but not vice-verse. See the parsing logic for
+      // details.
+      //
       else if (quote && (v.find_first_of (sc) != string::npos ||
                          (!pat && v.find_first_of (pc) != string::npos)))
       {
@@ -126,17 +159,32 @@ namespace build2
         if (escape) os << '\\';
         os << '\'';
       }
+      // Note that currently we do not preserve a leading `+` as a pattern
+      // unless it has other wildcard characters (see the parsing code for
+      // details). So we escape it both if it's not a pattern or is a path
+      // pattern.
+      //
+      else if (quote && ((!pat || *pat == pattern_type::path) &&
+                         ((v[0] == '+' && curly) || rc (v))))
+      {
+        if (escape) os << '\\';
+        os << '\\' << v;
+      }
       else
         os << v;
     };
 
     uint16_t dv (stream_verb (os).path); // Directory verbosity.
 
-    auto write_dir = [dv, quote, &os, &write_string] (const dir_path& d,
-                                                      bool pat)
+    auto write_dir = [&os, quote, &write_string, dv] (
+      const dir_path& d,
+      optional<pattern_type> pat = nullopt,
+      bool curly = false)
     {
       if (quote)
-        write_string (dv < 1 ? diag_relative (d) : d.representation (), pat);
+        write_string (dv < 1 ? diag_relative (d) : d.representation (),
+                      pat,
+                      curly);
       else
         os << d;
     };
@@ -151,7 +199,7 @@ namespace build2
 
     if (n.proj)
     {
-      write_string (n.proj->string (), false);
+      write_string (n.proj->string ());
       os << '%';
     }
 
@@ -171,29 +219,34 @@ namespace build2
                         dir_path ());
 
     if (!pd.empty ())
-      write_dir (pd, false);
+      write_dir (pd);
 
-    if (t || (!d && !v))
+    bool curly;
+    if ((curly = t || (!d && !v)))
     {
       if (t)
-        write_string (n.type, false);
+        write_string (n.type);
 
       os << '{';
     }
 
     if (v)
-      write_string (n.value, n.pattern);
+      write_string (n.value, n.pattern, curly);
     else if (d)
     {
+      // A directory pattern cannot be regex.
+      //
+      assert (!n.pattern || *n.pattern == pattern_type::path);
+
       if (rd.empty ())
-        write_string (dir_path (".").representation (), false);
+        write_string (dir_path (".").representation (), nullopt, curly);
       else if (!pd.empty ())
-        write_string (rd.leaf ().representation (), n.pattern);
+        write_string (rd.leaf ().representation (), n.pattern, curly);
       else
-        write_dir (rd, n.pattern);
+        write_dir (rd, n.pattern, curly);
     }
 
-    if (t || (!d && !v))
+    if (curly)
       os << '}';
 
     return os;
diff --git a/libbuild2/name.hxx b/libbuild2/name.hxx
index 5c76d07..216f207 100644
--- a/libbuild2/name.hxx
+++ b/libbuild2/name.hxx
@@ -33,16 +33,21 @@ namespace build2
   // If pair is not '\0', then this name and the next in the list form a
   // pair. Can be used as a bool flag.
   //
-  // If pattern is true then this is a name pattern (e.g., file{*.txt}).
+  // If pattern is present then this is a name pattern (e.g., file{*.txt},
+  // file{~'/(.+)\.txt/i'}, file{^'/\1/'}). A directory name cannot be a regex
+  // pattern (since we would need to store it in dir_path and a regex is not
+  // necessarily a valid path).
   //
   struct name
   {
+    enum class pattern_type: uint8_t {path, regex_pattern, regex_substitution};
+
     optional<project_name> proj;
     dir_path dir;
     string type;
     string value;
     char pair = '\0';
-    bool pattern = false;
+    optional<pattern_type> pattern;
 
     name () {} // = default; Clang needs this to initialize const object.
     name (string v): value (move (v)) {}
@@ -57,13 +62,16 @@ namespace build2
         : proj (project_name (move (p))), dir (move (d)), type (move (t)),
           value (move (v)) {}
 
-      name (optional<project_name> p,
-            dir_path d,
-            string t,
-            string v,
-            bool pat = false)
+    name (optional<project_name> p, dir_path d, string t, string v)
+        : proj (move (p)), dir (move (d)), type (move (t)), value (move (v)) {}
+
+    name (optional<project_name> p,
+          dir_path d,
+          string t,
+          string v,
+          optional<pattern_type> pt)
         : proj (move (p)), dir (move (d)), type (move (t)), value (move (v)),
-          pattern (pat) {}
+          pattern (pt) {}
 
     bool
     qualified () const {return proj.has_value ();}
@@ -162,7 +170,8 @@ namespace build2
     cs.append (n.type);
     cs.append (n.value);
     cs.append (n.pair);
-    cs.append (n.pattern);
+    if (n.pattern)
+      cs.append (static_cast<uint8_t> (*n.pattern));
   }
 
   // Store a string in a name in a reversible way. If the string ends with a
@@ -173,14 +182,21 @@ namespace build2
   to_name (string);
 
   // Serialize the name to the stream. If requested, the name components
-  // containing special characters are quoted. The special characters are:
+  // containing special characters are quoted and/or escaped. The special
+  // characters are:
   //
   // {}[]$() \t\n#\"'%
   //
-  // And additionally, if name is not a pattern:
+  // And additionally, unless name is a pattern:
   //
   // *?
   //
+  // As well as leading and if followed by a non-alphanumeric delimiter:
+  //
+  // ~^
+  //
+  // As well as leading `+` if in the curly braces.
+  //
   // If the pair argument is not '\0', then it is added to the above special
   // characters set. If the quote character is present in the component then
   // it is double quoted rather than single quoted. In this case the following
diff --git a/libbuild2/name.ixx b/libbuild2/name.ixx
index 80a097e..a3ee94b 100644
--- a/libbuild2/name.ixx
+++ b/libbuild2/name.ixx
@@ -21,7 +21,20 @@ namespace build2
       r = pair < x.pair ? -1 : (pair > x.pair ? 1 : 0);
 
     if (r == 0)
-      r = pattern == x.pattern ? 0 : (!pattern && x.pattern ? -1 : 1);
+    {
+      bool p (pattern);
+      bool xp (x.pattern);
+
+      r = p == xp ? 0 : (p ? 1 : -1);
+
+      if (r == 0 && p)
+      {
+        auto p (static_cast<uint8_t> (*pattern));
+        auto xp (static_cast<uint8_t> (*x.pattern));
+
+        r = p < xp ? -1 : (p > xp ? 1 : 0);
+      }
+    }
 
     return r;
   }
diff --git a/libbuild2/parser.cxx b/libbuild2/parser.cxx
index a9646d5..120d6ab 100644
--- a/libbuild2/parser.cxx
+++ b/libbuild2/parser.cxx
@@ -638,7 +638,9 @@ namespace build2
         // sensitive to the target context in which they are evaluated. The
         // function signature is:
         //
-        // void (token& t, type& tt, const target_type* type, string pat)
+        // void (token& t, type& tt,
+        //       optional<pattern_type>, const target_type* pat_tt, string pat,
+        //       const location& pat_loc)
         //
         // Note that the target and its ad hoc members are inserted implied
         // but this flag can be cleared and default_target logic applied if
@@ -695,42 +697,51 @@ namespace build2
               //
               // foo*/dir{*/}  --  foo*/*/dir{}
               //
-              if (n.value.empty () && !n.dir.empty ())
+              // Note also that none of this applies to regex patterns (see
+              // the parsing code for details).
+              //
+              if (*n.pattern == pattern_type::path)
               {
-                // Note that we use string and not the representation: in a
-                // sense the trailing slash in the pattern is subsumed by the
-                // target type.
-                //
-                if (n.dir.simple ())
-                  n.value = move (n.dir).string ();
-                else
+                if (n.value.empty () && !n.dir.empty ())
                 {
-                  n.value = n.dir.leaf ().string ();
-                  n.dir.make_directory ();
-                }
+                  // Note that we use string and not the representation: in a
+                  // sense the trailing slash in the pattern is subsumed by
+                  // the target type.
+                  //
+                  if (n.dir.simple ())
+                    n.value = move (n.dir).string ();
+                  else
+                  {
+                    n.value = n.dir.leaf ().string ();
+                    n.dir.make_directory ();
+                  }
 
-                // Treat directory as type dir{} similar to other places.
-                //
-                if (n.untyped ())
-                  n.type = "dir";
-              }
-              else
-              {
-                // Move the directory part, if any, from value to dir.
-                //
-                try
-                {
-                  n.canonicalize ();
-                }
-                catch (const invalid_path& e)
-                {
-                  fail (nloc) << "invalid path '" << e.path << "'";
+                  // Treat directory as type dir{} similar to other places.
+                  //
+                  if (n.untyped ())
+                    n.type = "dir";
                 }
-                catch (const invalid_argument&)
+                else
                 {
-                  fail (nloc) << "invalid pattern '" << n.value << "'";
+                  // Move the directory part, if any, from value to dir.
+                  //
+                  try
+                  {
+                    n.canonicalize ();
+                  }
+                  catch (const invalid_path& e)
+                  {
+                    fail (nloc) << "invalid path '" << e.path << "'";
+                  }
+                  catch (const invalid_argument&)
+                  {
+                    fail (nloc) << "invalid pattern '" << n.value << "'";
+                  }
                 }
               }
+              else if (*n.pattern == pattern_type::regex_substitution)
+                fail (nloc) << "regex substitution " << n << " without "
+                            << "regex pattern";
 
               // If we have the directory, then it is the scope.
               //
@@ -760,7 +771,7 @@ namespace build2
               if (ti == nullptr)
                 fail (nloc) << "unknown target type " << n.type;
 
-              f (t, tt, ti, move (n.value));
+              f (t, tt, n.pattern, ti, move (n.value), nloc);
             }
             else
             {
@@ -781,7 +792,7 @@ namespace build2
                 enter_adhoc_members (move (ans[i]), true /* implied */);
               }
 
-              f (t, tt, nullptr, string ());
+              f (t, tt, nullopt, nullptr, string (), location ());
             }
 
             if (++i != e)
@@ -832,7 +843,8 @@ namespace build2
               st = token (t), // Save start token (will be gone on replay).
               recipes = small_vector<shared_ptr<adhoc_rule>, 1> ()]
               (token& t, type& tt,
-               const target_type* type, string pat) mutable
+               optional<pattern_type> pt, const target_type* ptt, string pat,
+               const location& ploc) mutable
             {
               token rt; // Recipe start token.
 
@@ -842,7 +854,7 @@ namespace build2
               {
                 next (t, tt); // Newline.
                 next (t, tt); // First token inside the variable block.
-                parse_variable_block (t, tt, type, move (pat));
+                parse_variable_block (t, tt, pt, ptt, move (pat), ploc);
 
                 if (tt != type::rcbrace)
                   fail (t) << "expected '}' instead of " << t;
@@ -858,7 +870,7 @@ namespace build2
               else
                 rt = st;
 
-              if (type != nullptr)
+              if (pt)
                 fail (rt) << "recipe in target type/pattern";
 
               parse_recipe (t, tt, rt, recipes);
@@ -921,17 +933,19 @@ namespace build2
 
           // Parse the assignment for each target.
           //
-          for_each ([this, &var, akind, &aloc] (token& t, type& tt,
-                                                const target_type* type,
-                                                string pat)
-                    {
-                      if (type == nullptr)
-                        parse_variable (t, tt, var, akind);
-                      else
-                        parse_type_pattern_variable (t, tt,
-                                                     *type, move (pat),
-                                                     var, akind, aloc);
-                    });
+          for_each (
+            [this, &var, akind, &aloc] (
+              token& t, type& tt,
+              optional<pattern_type> pt, const target_type* ptt, string pat,
+              const location& ploc)
+            {
+              if (pt)
+                parse_type_pattern_variable (t, tt,
+                                             *pt, *ptt, move (pat), ploc,
+                                             var, akind, aloc);
+              else
+                parse_variable (t, tt, var, akind);
+            });
 
           next_after_newline (t, tt);
         }
@@ -1110,7 +1124,8 @@ namespace build2
 
   void parser::
   parse_variable_block (token& t, type& tt,
-                        const target_type* type, string pat)
+                        optional<pattern_type> pt, const target_type* ptt,
+                        string pat, const location& ploc)
   {
     // Parse a target or prerequisite-specific variable block. If type is not
     // NULL, then this is a target type/pattern-specific block.
@@ -1148,12 +1163,12 @@ namespace build2
                  << " visibility but is assigned on a target";
       }
 
-      if (type == nullptr)
-        parse_variable (t, tt, var, tt);
-      else
+      if (pt)
         parse_type_pattern_variable (t, tt,
-                                     *type, pat, // Note: can't move.
+                                     *pt, *ptt, pat, ploc, // Note: can't move.
                                      var, tt, get_location (t));
+      else
+        parse_variable (t, tt, var, tt);
 
       if (tt != type::newline)
         fail (t) << "expected newline instead of " << t;
@@ -3835,24 +3850,34 @@ namespace build2
   }
 
   void parser::
-  parse_type_pattern_variable (token& t, token_type& tt,
-                               const target_type& type, string pat,
-                               const variable& var, token_type kind,
-                               const location& loc)
+  parse_type_pattern_variable (
+    token& t, token_type& tt,
+    pattern_type pt, const target_type& ptt, string pat, const location& ploc,
+    const variable& var, token_type kind, const location& loc)
   {
     // Parse target type/pattern-specific variable assignment.
     //
-    // See old-tests/variable/type-pattern.
 
     // Note: expanding the value in the current scope context.
     //
     value rhs (parse_variable_value (t, tt));
 
-    // Leave the value untyped unless we are assigning.
-    //
-    pair<reference_wrapper<value>, bool> p (
-      scope_->target_vars[type][move (pat)].insert (
-        var, kind == type::assign));
+    pair<reference_wrapper<value>, bool> p (rhs /* dummy */, false);
+    try
+    {
+      // Leave the value untyped unless we are assigning.
+      //
+      // Note that the pattern is preserved if insert fails with regex_error.
+      //
+      p = scope_->target_vars[ptt].insert (pt, move (pat)).insert (
+        var, kind == type::assign);
+    }
+    catch (const regex_error& e)
+    {
+      // Print regex_error description if meaningful (no space).
+      //
+      fail (ploc) << "invalid regex pattern '" << pat << "'" << e;
+    }
 
     value& lhs (p.first);
 
@@ -4676,7 +4701,7 @@ namespace build2
                dir_path d,
                string t,
                string v,
-               bool pat,
+               optional<name::pattern_type> pat,
                const location& loc)
   {
     // The directory/value must not be empty if we have a type.
@@ -4792,8 +4817,9 @@ namespace build2
       }
 
       name& r (
-        append_name (
-          ns, move (p), move (d), move (t), move (v), cn.pattern, loc));
+        append_name (ns,
+                     move (p), move (d), move (t), move (v), cn.pattern,
+                     loc));
       r.pair = cn.pair;
     }
 
@@ -5492,6 +5518,7 @@ namespace build2
 
     // Return '+' or '-' if a token can start an inclusion or exclusion
     // (pattern or group), '\0' otherwise. The result can be used as bool.
+    // Note that token::qfirst covers both quoting and escaping.
     //
     auto pattern_prefix = [] (const token& t) -> char
     {
@@ -5758,9 +5785,9 @@ namespace build2
 
         // Find a separator (slash or %).
         //
-        string::size_type p (separators != nullptr
-                             ? val.find_last_of (*separators)
-                             : string::npos);
+        string::size_type pos (separators != nullptr
+                               ? val.find_last_of (*separators)
+                               : string::npos);
 
         // First take care of project. A project-qualified name is not very
         // common, so we can afford some copying for the sake of simplicity.
@@ -5768,10 +5795,10 @@ namespace build2
         optional<project_name> p1;
         const optional<project_name>* pp1 (&pp);
 
-        if (p != string::npos)
+        if (pos != string::npos)
         {
-          bool last (val[p] == '%');
-          string::size_type q (last ? p : val.rfind ('%', p - 1));
+          bool last (val[pos] == '%');
+          string::size_type q (last ? pos : val.rfind ('%', pos - 1));
 
           for (; q != string::npos; ) // Breakout loop.
           {
@@ -5801,13 +5828,13 @@ namespace build2
             // Now fix the rest of the name.
             //
             val.erase (0, q + 1);
-            p = last ? string::npos : p - (q + 1);
+            pos = last ? string::npos : pos - (q + 1);
 
             break;
           }
         }
 
-        string::size_type n (p != string::npos ? val.size () - 1 : 0);
+        size_t size (pos != string::npos ? val.size () - 1 : 0);
 
         // See if this is a type name, directory prefix, or both. That
         // is, it is followed by an un-separated '{'.
@@ -5834,7 +5861,7 @@ namespace build2
             }
           }
 
-          if (p != n && tp != nullptr && !pinc)
+          if (pos != size && tp != nullptr && !pinc)
             fail (loc) << "nested type name " << val;
 
           dir_path d1;
@@ -5845,9 +5872,9 @@ namespace build2
 
           try
           {
-            if (p == string::npos) // type
+            if (pos == string::npos) // type
               tp1 = &val;
-            else if (p == n) // directory
+            else if (pos == size) // directory
             {
               if (dp == nullptr)
                 d1 = dir_path (val);
@@ -5858,12 +5885,12 @@ namespace build2
             }
             else // both
             {
-              t1.assign (val, p + 1, n - p);
+              t1.assign (val, pos + 1, size - pos);
 
               if (dp == nullptr)
-                d1 = dir_path (val, 0, p + 1);
+                d1 = dir_path (val, 0, pos + 1);
               else
-                d1 = *dp / dir_path (val, 0, p + 1);
+                d1 = *dp / dir_path (val, 0, pos + 1);
 
               dp1 = &d1;
               tp1 = &t1;
@@ -5893,102 +5920,212 @@ namespace build2
           continue;
         }
 
-        // See if this is a wildcard pattern.
+        // See if this is a pattern, path or regex.
+        //
+        // A path pattern either contains an unquoted wildcard character or,
+        // in the curly context, start with unquoted/unescaped `+`.
+        //
+        // A regex pattern starts with unquoted/unescaped `~` followed by a
+        // non-alphanumeric delimiter and has the following form:
+        //
+        // ~/<pat>/[<flags>]
+        //
+        // A regex substitution starts with unquoted/unescaped '^' followed by
+        // a non-alphanumeric delimiter and has the follwing form:
+        //
+        // ^/<sub>/[<flags>]
+        //
+        // Any non-alphanumeric character other that `/` can be used as a
+        // delimiter but escaping of the delimiter character is not supported
+        // (one benefit of this is that we can store and print the pattern as
+        // is without worrying about escaping; the non-alphanumeric part is to
+        // allow values like ~host and ^cat).
         //
-        // It should either contain a wildcard character or, in a curly
-        // context, start with unquoted '+'.
+        // The following pattern flags are recognized:
         //
-        // Note that in the general case we need to convert it to a path prior
-        // to testing for being a pattern (think of b[a/r] that is not a
-        // pattern). If the conversion fails then this is not a path pattern.
+        // i -- match ignoring case
+        // e -- match including extension
         //
-        auto pattern = [&val, &loc, this] ()
+        // Note that we cannot express certain path patterns that start with
+        // the regex introducer using quoting (for example, `~*`) since
+        // quoting prevents the whole from being recognized as a path
+        // pattern. However, we can achieve this with escaping (for example,
+        // \~*). This works automatically since we treat (at the lexer level)
+        // escaped first characters as quoted without treating the whole thing
+        // as quoted. Note that there is also the corresponding logic in
+        // to_stream(name).
+        //
+        // A pattern cannot be project-qualified.
+        //
+        optional<pattern_type> pat;
+
+        if (pmode != pattern_mode::ignore && !*pp1)
         {
-          // Let's optimize it a bit for the common cases.
+          // Note that in the general case we need to convert it to a path
+          // prior to testing for being a pattern (think of b[a/r] that is not
+          // a pattern).
           //
-          if (val.find_first_of ("*?[") == string::npos)
-            return false;
+          auto path_pattern = [&val, &loc, this] ()
+          {
+            // Let's optimize it a bit for the common cases.
+            //
+            if (val.find_first_of ("*?[") == string::npos)
+              return false;
 
-          if (path::traits_type::find_separator (val) == string::npos)
-            return path_pattern (val);
+            if (path_traits::find_separator (val) == string::npos)
+              return build2::path_pattern (val);
 
-          try
-          {
-            return path_pattern (path (val));
-          }
-          catch (const invalid_path& e)
+            try
+            {
+              return build2::path_pattern (path (val));
+            }
+            catch (const invalid_path& e)
+            {
+              fail (loc) << "invalid path '" << e.path << "'" << endf;
+            }
+          };
+
+          auto regex_pattern = [&val] ()
           {
-            fail (loc) << "invalid path '" << e.path << "'" << endf;
-          }
-        };
+            return ((val[0] == '~' || val[0] == '^') &&
+                    val[1] != '\0' && !alnum (val[1]));
+          };
 
-        bool pat (false);
-        if (pmode == pattern_mode::expand || pmode == pattern_mode::detect)
-        {
-          if (!*pp1    && // Cannot be project-qualified.
-              !quoted  && // Cannot be quoted.
-              ((dp != nullptr && dp->absolute ()) || pbase_ != nullptr) &&
-              (pattern () || (curly && val[0] == '+')))
+          if (pmode != pattern_mode::preserve)
           {
-            // Resolve the target type if there is one. If we fail, then this
-            // is not a pattern.
+            // Note that if we have no base directory or cannot resolve the
+            // target type, then this affectively becomes the ignore mode.
             //
-            const target_type* ttp (tp != nullptr && scope_ != nullptr
-                                    ? scope_->find_target_type (*tp)
-                                    : nullptr);
-
-            if (tp == nullptr || ttp != nullptr)
+            if (pbase_ != nullptr || (dp != nullptr && dp->absolute ()))
             {
-              if (pmode == pattern_mode::detect)
+              // Note that we have to check for regex patterns first since
+              // they may also be detected as path patterns.
+              //
+              if (!quoted_first && regex_pattern ())
               {
-                // Strip the literal unquoted plus character for the first
-                // pattern in the group.
+                // Note: we may decide to support regex-based name generation
+                // some day (though a substitution won't make sense here).
                 //
-                if (ppat)
-                {
-                  assert (val[0] == '+');
+                fail (loc) << "regex pattern-based name generation" <<
+                  info << "quote '" << val << "' (or escape first character) "
+                       << "to treat it as literal name (or path pattern)";
+              }
+              else if ((!quoted && path_pattern ()) ||
+                       (!quoted_first && curly && val[0] == '+'))
+              {
+                // Resolve the target type if there is one.
+                //
+                const target_type* ttp (tp != nullptr && scope_ != nullptr
+                                        ? scope_->find_target_type (*tp)
+                                        : nullptr);
 
-                  val.erase (0, 1);
-                  ppat = pinc = false;
+                if (tp == nullptr || ttp != nullptr)
+                {
+                  if (pmode == pattern_mode::detect)
+                  {
+                    // Strip the literal unquoted plus character for the first
+                    // pattern in the group.
+                    //
+                    if (ppat)
+                    {
+                      assert (val[0] == '+');
+                      val.erase (0, 1);
+                      ppat = pinc = false;
+                    }
+
+                    // Set the detect pattern mode to expand if the pattern is
+                    // not followed by the inclusion/exclusion pattern/match.
+                    // Note that if it is '}' (i.e., the end of the group),
+                    // then it is a single pattern and the expansion is what
+                    // we want.
+                    //
+                    if (!pattern_prefix (peeked ()))
+                      pmode = pattern_mode::expand;
+                  }
+
+                  if (pmode == pattern_mode::expand)
+                  {
+                    count = expand_name_pattern (get_location (t),
+                                                 names {name (move (val))},
+                                                 ns,
+                                                 what,
+                                                 pairn,
+                                                 dp, tp, ttp);
+                    continue;
+                  }
+
+                  pattern_detected (ttp);
+
+                  // Fall through.
                 }
+              }
+            }
+          }
+          else
+          {
+            // For the preserve mode we treat it as a pattern if it look like
+            // one syntactically. For now we also don't treat leading `+` in
+            // the curly context as an indication of a path pattern (since
+            // there isn't any good reason to; see also to_stream(name) for
+            // the corresponding serialization logic).
+            //
+            if (!quoted_first && regex_pattern ())
+            {
+              const char* w;
+              if (val[0] == '~')
+              {
+                w = "regex pattern";
+                pat = pattern_type::regex_pattern;
+              }
+              else
+              {
+                w = "regex substitution";
+                pat = pattern_type::regex_substitution;
+              }
 
-                // Reset the detect pattern mode to expand if the pattern is
-                // not followed by the inclusion/exclusion pattern/match. Note
-                // that if it is '}' (i.e., the end of the group), then it is
-                // a single pattern and the expansion is what we want.
-                //
-                if (!pattern_prefix (peeked ()))
-                  pmode = pattern_mode::expand;
+              size_t n (val.size ());
+
+              // Verify delimiters and find the position of the flags.
+              //
+              char d (val[1]);
+              size_t p (val.rfind (d));
+
+              if (p == 1)
+              {
+                fail (loc) << "no trailing delimiter '" << d << "' in "
+                           << w << " '" << val << "'" <<
+                  info << "quote '" << val << "' (or escape first character) "
+                       << "to treat it as literal name (or path pattern)";
               }
 
-              if (pmode == pattern_mode::expand)
+              // Verify flags.
+              //
+              for (size_t i (++p); i != n; ++i)
               {
-                count = expand_name_pattern (get_location (t),
-                                             names {name (move (val))},
-                                             ns,
-                                             what,
-                                             pairn,
-                                             dp, tp, ttp);
-                continue;
+                char f (val[i]);
+
+                if (*pat == pattern_type::regex_pattern)
+                {
+                  if (f == 'i' || f == 'e')
+                    continue;
+                }
+
+                fail (loc) << "unknown flag '" << f << "' in " << w << " '"
+                           << val << "'";
               }
 
-              pattern_detected (ttp);
+              val.erase (0, 1); // Remove `~` or `^`.
 
-              // Fall through.
+              // Make sure we don't treat something like `~/.../` as a
+              // directory.
+              //
+              pos = string::npos;
+              size = 0;
             }
+            else if (!quoted && path_pattern ())
+              pat = pattern_type::path;
           }
         }
-        else if (pmode == pattern_mode::preserve)
-        {
-          // For the preserve mode we treat it as a pattern if it look like
-          // one syntactically. For now we also don't treat leading `+` in the
-          // curly context as an indication of a pattern.
-          //
-          if (!*pp1   && // Cannot be project-qualified.
-              !quoted && // Cannot be quoted.
-              pattern ())
-            pat = true;
-        }
 
         // If we are a second half of a pair, add another first half
         // unless this is the first instance.
@@ -6006,7 +6143,9 @@ namespace build2
         // in scope::find_target_type(). This would also mess up
         // reversibility to simple name.
         //
-        if (p == n)
+        // Note: a regex pattern cannot be a directory (see above).
+        //
+        if (pos == size)
         {
           // For reversibility to simple name, only treat it as a directory
           // if the string is an exact representation.
@@ -6021,8 +6160,7 @@ namespace build2
             append_name (
               ns,
               *pp1, move (dir), (tp != nullptr ? *tp : string ()), string (),
-              pat,
-              loc);
+              pat, loc);
 
             continue;
           }
@@ -6568,7 +6706,7 @@ namespace build2
                          (dp != nullptr ? *dp : dir_path ()),
                          (tp != nullptr ? *tp : string ()),
                          string (),
-                         false /* pattern */,
+                         nullopt, /* pattern */
                          get_location (t));
             count = 1;
           }
@@ -6589,7 +6727,7 @@ namespace build2
                          (dp != nullptr ? *dp : dir_path ()),
                          (tp != nullptr ? *tp : string ()),
                          string (),
-                         false /* pattern */,
+                         nullopt, /* pattern */
                          get_location (t));
             count = 0;
           }
@@ -6617,7 +6755,7 @@ namespace build2
                      (dp != nullptr ? *dp : dir_path ()),
                      (tp != nullptr ? *tp : string ()),
                      string (),
-                     false /* pattern */,
+                     nullopt, /* pattern */
                      get_location (t));
         break;
       }
@@ -6636,7 +6774,7 @@ namespace build2
                    (dp != nullptr ? *dp : dir_path ()),
                    (tp != nullptr ? *tp : string ()),
                    string (),
-                   false /* pattern */,
+                   nullopt, /* pattern */
                    get_location (t));
     }
 
diff --git a/libbuild2/parser.hxx b/libbuild2/parser.hxx
index 889d339..007e508 100644
--- a/libbuild2/parser.hxx
+++ b/libbuild2/parser.hxx
@@ -103,6 +103,7 @@ namespace build2
     // Recursive descent parser.
     //
   protected:
+    using pattern_type = name::pattern_type;
 
     // Pattern expansion mode.
     //
@@ -129,8 +130,10 @@ namespace build2
 
     void
     parse_variable_block (token&, token_type&,
-                          const target_type* = nullptr,
-                          string = string ());
+                          optional<pattern_type> = {},
+                          const target_type*  = nullptr,
+                          string = {},
+                          const location& = {});
 
     void
     parse_recipe (token&, token_type&,
@@ -223,9 +226,10 @@ namespace build2
     parse_variable (token&, token_type&, const variable&, token_type);
 
     void
-    parse_type_pattern_variable (token&, token_type&,
-                                 const target_type&, string,
-                                 const variable&, token_type, const location&);
+    parse_type_pattern_variable (
+      token&, token_type&,
+      pattern_type, const target_type&, string, const location&,
+      const variable&, token_type, const location&);
 
     const variable&
     parse_variable_name (names&&, const location&);
diff --git a/libbuild2/scope.cxx b/libbuild2/scope.cxx
index 46e3dcd..f2700c4 100644
--- a/libbuild2/scope.cxx
+++ b/libbuild2/scope.cxx
@@ -49,7 +49,7 @@ namespace build2
                                  const scope* s,
                                  const target_key* tk,
                                  const target_key* gk,
-                                 optional<string> n)
+                                 string n)
     {
       const value& v (*l);
       assert ((v.extra == 1 || v.extra == 2) && v.type == nullptr);
@@ -70,7 +70,7 @@ namespace build2
       pair<value&, ulock> entry (
         s->target_vars.cache.insert (
           ctx,
-          make_tuple (&v, tk->type, n && !n->empty () ? move (*n) : *tk->name),
+          make_tuple (&v, tk->type, !n.empty () ? move (n) : *tk->name),
           stem,
           static_cast<const variable_map::value_data&> (v).version,
           var));
@@ -146,7 +146,7 @@ namespace build2
             if (l.defined ())
             {
               if (l->extra != 0) // Prepend/append?
-                pre_app (l, s, tk, gk, move (tn));
+                pre_app (l, s, tk, gk, move (*tn));
 
               return make_pair (move (l), d);
             }
@@ -164,7 +164,7 @@ namespace build2
             if (l.defined ())
             {
               if (l->extra != 0) // Prepend/append?
-                pre_app (l, s, gk, nullptr, move (gn));
+                pre_app (l, s, gk, nullptr, move (*gn));
 
               return make_pair (move (l), d);
             }
diff --git a/libbuild2/token.hxx b/libbuild2/token.hxx
index faae466..fca888c 100644
--- a/libbuild2/token.hxx
+++ b/libbuild2/token.hxx
@@ -120,7 +120,8 @@ namespace build2
     // Quoting can be complete, where the token starts and ends with the quote
     // characters and quoting is contiguous or partial where only some part(s)
     // of the token are quoted or quoting continues to the next token. We also
-    // keep track whether the first character of a token is quoted.
+    // keep track whether the first character of a token is quoted (we also
+    // treat escaped first character as quoted).
     //
     quote_type qtype;
     bool qcomp;
diff --git a/libbuild2/types.hxx b/libbuild2/types.hxx
index dd82ef1..8dfda6e 100644
--- a/libbuild2/types.hxx
+++ b/libbuild2/types.hxx
@@ -16,6 +16,7 @@
 #include <map>
 #include <array>
 #include <tuple>
+#include <regex>
 #include <vector>
 #include <string>
 #include <memory>           // unique_ptr, shared_ptr
@@ -44,6 +45,7 @@
 
 #include <libbutl/path.mxx>
 #include <libbutl/path-map.mxx>
+#include <libbutl/regex.mxx>
 #include <libbutl/sha256.mxx>
 #include <libbutl/process.mxx>
 #include <libbutl/fdstream.mxx>
@@ -105,6 +107,14 @@ namespace build2
   using std::endl;
   using std::streamsize; // C++'s ssize_t.
 
+  // Regex.
+  //
+  // Note that <libbutl/regex.mxx> includes an ostream insertion operator for
+  // regex_error which prints cleaned up message, if any.
+  //
+  using std::regex;
+  using std::regex_error;
+
   // Concurrency.
   //
   using std::atomic;
diff --git a/libbuild2/variable.cxx b/libbuild2/variable.cxx
index 3e3bf05..1855f3e 100644
--- a/libbuild2/variable.cxx
+++ b/libbuild2/variable.cxx
@@ -1796,6 +1796,51 @@ namespace build2
     return m_.erase (var) != 0;
   }
 
+  // variable_pattern_map
+  //
+  variable_map& variable_pattern_map::
+  insert (pattern_type type, string&& text)
+  {
+    auto r (map_.emplace (pattern {type, false, move (text), {}},
+                          variable_map (ctx, global_)));
+
+    // Compile the regex.
+    //
+    if (r.second && type == pattern_type::regex_pattern)
+    {
+      // On exception restore the text argument (so that it's available for
+      // diagnostics) and remove the element from the map.
+      //
+      auto eg (make_exception_guard (
+                 [&text, &r, this] ()
+                 {
+                   text = r.first->first.text;
+                   map_.erase (r.first);
+                 }));
+
+      const string& t (r.first->first.text);
+      size_t n (t.size ()), p (t.rfind (t[0]));
+
+      // Convert flags.
+      //
+      regex::flag_type f (regex::ECMAScript);
+      for (size_t i (p + 1); i != n; ++i)
+      {
+        switch (t[i])
+        {
+        case 'i': f |= regex::icase;               break;
+        case 'e': r.first->first.match_ext = true; break;
+        }
+      }
+
+      // Skip leading delimiter as well as trailing delimiter and flags.
+      //
+      r.first->first.regex = regex (t.c_str () + 1, p - 1, f);
+    }
+
+    return r.first->second;
+  }
+
   // variable_type_map
   //
   lookup variable_type_map::
@@ -1805,6 +1850,8 @@ namespace build2
   {
     // Compute and cache "effective" name that we will be matching.
     //
+    // See also the additional match_ext logic below.
+    //
     auto name = [&tk, &oname] () -> const string&
     {
       if (!oname)
@@ -1856,24 +1903,40 @@ namespace build2
       if (i == end ())
         continue;
 
-      // Try to match the pattern, starting from the longest values
-      // so that the more "specific" patterns (i.e., those that cover
-      // fewer characters with the wildcard) take precedence. See
-      // tests/variable/type-pattern.
+      // Try to match the pattern, starting from the longest values.
       //
       const variable_pattern_map& m (i->second);
-
       for (auto j (m.rbegin ()); j != m.rend (); ++j)
       {
-        const string& pat (j->first);
+        using pattern = variable_pattern_map::pattern;
+        using pattern_type = variable_pattern_map::pattern_type;
 
-        //@@ TODO: should we detect ambiguity? 'foo-*' '*-foo' and 'foo-foo'?
-        //   Right now the last defined will be used.
-        //
-        if (pat != "*")
+        const pattern& pat (j->first);
+
+        bool r, e (false);
+        if (pat.type == pattern_type::path)
+        {
+          r = pat.text == "*" || butl::path_match (name (), pat.text);
+        }
+        else
         {
-          if (!butl::path_match (name (), pat))
-            continue;
+          const string& n (name ());
+
+          // Deal with match_ext: first see if the extension would be added by
+          // default. If not, then temporarily add it in oname and then clean
+          // it up if there is no match (to prevent another pattern from using
+          // it). While we may keep adding it if there are multiple patterns
+          // with such a flag, we will at least reuse the buffer in oname.
+          //
+          e = pat.match_ext && tk.ext && !tk.ext->empty () && oname->empty ();
+          if (e)
+          {
+            *oname = *tk.name;
+            *oname += '.';
+            *oname += *tk.ext;
+          }
+
+          r = regex_match (e ? *oname : n, *pat.regex);
         }
 
         // Ok, this pattern matches. But is there a variable?
@@ -1882,8 +1945,9 @@ namespace build2
         // to automatically type it. And if it is assignment, then typify it
         // ourselves.
         //
-        const variable_map& vm (j->second);
+        if (r)
         {
+          const variable_map& vm (j->second);
           auto p (vm.lookup (var, false));
           if (const variable_map::value_data* v = p.first)
           {
@@ -1895,12 +1959,15 @@ namespace build2
             // Make sure the effective name is computed if this is
             // append/prepend (it is used as a cache key).
             //
-            if (v->extra != 0)
+            if (v->extra != 0 && !oname)
               name ();
 
             return lookup (*v, p.second, vm);
           }
         }
+
+        if (e)
+          oname->clear ();
       }
     }
 
diff --git a/libbuild2/variable.hxx b/libbuild2/variable.hxx
index a272013..573f968 100644
--- a/libbuild2/variable.hxx
+++ b/libbuild2/variable.hxx
@@ -1740,17 +1740,69 @@ namespace build2
   class variable_pattern_map
   {
   public:
-    using map_type = map<string, variable_map>;
+    using pattern_type = name::pattern_type;
+
+    // We use the map to keep the patterns in the shortest-first order. This
+    // is used during match where we starting from the longest values so that
+    // the more "specific" patterns (i.e., those that cover fewer characters
+    // with the wildcard) take precedence.
+    //
+    // Note that this is only an approximation (e.g., `*[0-9]` vs `[0-9]`) but
+    // it's sufficient in practice (e.g., `*` vs `*.txt`). We also have the
+    // ambiguity problem (e.g., `foo-foo` matching both `foo-*` and `*-foo`).
+    //
+    // And, of course, this doesn't apply accross pattern types so we always
+    // treat regex patterns as more specific than path patterns.
+    //
+    // While it feels like this should be a union (with pattern_type as the
+    // discriminator), we need to keep the original regex text for dumping.
+    // So we just keep optional<regex> which is absent for path patterns (it's
+    // optional since a default-constructed regex has a pattern). BTW, the
+    // size of std::regex object ranges between 32 and 64 bytes, depending on
+    // the implementation.
+    //
+    struct pattern
+    {
+      pattern_type                    type;
+      mutable bool                    match_ext; // Match extension flag.
+      string                          text;
+      mutable optional<build2::regex> regex;
+    };
+
+    struct pattern_compare
+    {
+      bool operator() (const pattern& x, const pattern& y) const
+      {
+        return x.type != y.type
+          ? x.type == pattern_type::path
+          : (x.text.size () != y.text.size ()
+             ? x.text.size () < y.text.size ()
+             : x.text < y.text);
+      }
+    };
+
+    using map_type = map<pattern, variable_map, pattern_compare>;
     using const_iterator = map_type::const_iterator;
     using const_reverse_iterator = map_type::const_reverse_iterator;
 
     variable_pattern_map (context& c, bool global)
         : ctx (c), global_ (global) {}
 
+    // Note that here we assume the "outer" pattern format (delimiters, flags,
+    // etc) is valid.
+    //
+    // Note: may throw regex_error in which case text is preserved.
+    //
+    variable_map&
+    insert (pattern_type type, string&& text);
+
+    // Convenience shortcut or path patterns.
+    //
     variable_map&
-    operator[] (const string& v)
+    operator[] (string text)
     {
-      return map_.emplace (v, variable_map (ctx, global_)).first->second;
+      return map_.emplace (pattern {pattern_type::path, false, move (text), {}},
+                           variable_map (ctx, global_)).first->second;
     }
 
     const_iterator         begin ()  const {return map_.begin ();}
@@ -1769,7 +1821,7 @@ namespace build2
   {
   public:
     using map_type = map<reference_wrapper<const target_type>,
-                              variable_pattern_map>;
+                         variable_pattern_map>;
     using const_iterator = map_type::const_iterator;
 
     variable_type_map (context& c, bool global): ctx (c), global_ (global) {}
@@ -1785,6 +1837,10 @@ namespace build2
     const_iterator end ()   const {return map_.end ();}
     bool           empty () const {return map_.empty ();}
 
+    // If found append/prepend then name is guaranteed to either contain the
+    // full name that was used for the match or be empty in which case the
+    // orginal target name was used.
+    //
     lookup
     find (const target_key&, const variable&, optional<string>& name) const;
 
diff --git a/old-tests/variable/type-pattern/buildfile b/old-tests/variable/type-pattern/buildfile
deleted file mode 100644
index dd218ac..0000000
--- a/old-tests/variable/type-pattern/buildfile
+++ /dev/null
@@ -1,39 +0,0 @@
-#dir/foo{*}: x = y # directory
-#foo{*.*}: x = y # multiple wildcards
-#foo{*}: x = y # unknown target type
-#file{*}: x += y # append
-
-# Use --verbose 6 to examine.
-#
-
-dir{*}: x = y
-
-x = z
-dir{*-foo}: x = $x # 'z'
-
-x = G
-file{*-foo}: x = x
-file{xfoo}: x = $x      # 'G'
-file{-foo}: x = $x      # 'x'
-file{x-foo}: x = $x     # 'x'
-file{bar-*-foo}: x = X
-file{bar-x}: x = $x     # 'G'
-file{bar--foo}: x = $x  # 'X'
-file{bar-x-foo}: x = $x # 'X'
-
-file{*-fox}: x = 1
-file{fox-*}: x = 2
-file{fox-fox}: x = $x # '2'
-file{*-fox}: x = 3
-file{fox-x-fox}: x = $x # still '2'!
-
-*-foz: x = z        # any target
-file{x-foz}: x = $x # 'z'
-
-# These should all be the same.
-#
-*: x1 = X1
-{*}: x2 = X2
-*{*}: x3 = X3
-
-./:
diff --git a/tests/variable/target-type-pattern-specific/testscript b/tests/variable/target-type-pattern-specific/testscript
index 1a3e98a..9962342 100644
--- a/tests/variable/target-type-pattern-specific/testscript
+++ b/tests/variable/target-type-pattern-specific/testscript
@@ -19,6 +19,65 @@ X
 y Y
 EOO
 
+: old-tests-type-pattern
+:
+$* <<EOI >>EOO
+dir{*}: x = y
+
+x = z
+dir{*-foo}: x = $x # 'z'
+print $(bar-foo/: x)
+
+x = G
+file{*-foo}: x = x
+file{xfoo}: x = $x      # 'G'
+print $(file{xfoo}: x)
+file{-foo}: x = $x      # 'x'
+print $(file{-foo}: x)
+file{x-foo}: x = $x     # 'x'
+print $(file{x-foo}: x)
+file{bar-*-foo}: x = X
+file{bar-x}: x = $x     # 'G'
+print $(file{bar-x}: x)
+file{bar--foo}: x = $x  # 'X'
+print $(file{bar--foo}: x)
+file{bar-x-foo}: x = $x # 'X'
+print $(file{bar-x-foo}: x)
+
+file{*-fox}: x = 1
+file{fox-*}: x = 2
+file{fox-fox}: x = $x # '2'
+print $(file{fox-fox}: x)
+file{*-fox}: x = 3
+file{fox-x-fox}: x = $x # still '2'!
+print $(file{fox-fox}: x)
+
+*-foz: x = z        # any target
+file{x-foz}: x = $x # 'z'
+print $(file{x-foz}: x)
+
+*: x1 = X1
+{*}: x2 = X2
+*{*}: x3 = X3
+print $(file{x}: x1)
+print $(file{x}: x2)
+print $(file{x}: x3)
+EOI
+z
+G
+x
+x
+G
+X
+X
+2
+2
+z
+X1
+X2
+X3
+EOO
+
 : block
 :
 $* <<EOI >>EOO
@@ -55,3 +114,71 @@ EOI
 X
 y Y
 EOO
+
+: regex
+:
+{
+  : flag-icase
+  :
+  $* <<EOI >>EOO
+  file{~/'.+\.txt'/i}: x = 1
+
+  print $(file{foo.txt}: x)
+  print $(file{foo.TXT}: x)
+  EOI
+  1
+  1
+  EOO
+
+  : flag-match-ext
+  :
+  $* <<EOI >>EOO
+  define txt: file
+
+  txt{*}:             x = 0
+  txt{~/'[^.]+'/}:    x = 1
+  txt{~/'.+\.tx'/e}:  x = 2
+  txt{~/'.+\.txt'/e}: x = 3
+
+  print $(txt{foo.x}: x)
+  print $(txt{foo.tx}: x)
+  print $(txt{foo.txt}: x)
+  print $(txt{foo.bar...}: x)
+  EOI
+  1
+  2
+  3
+  0
+  EOO
+
+  : backref
+  :
+  $* <<EOI >>EOO
+  x = 0
+  file{~/'(.+)-\1'/}: x = 1
+
+  print $(file{foo-foo}: x)
+  print $(file{foo-bar}: x)
+  EOI
+  1
+  0
+  EOO
+
+  : dir
+  :
+  $* <<EOI >>EOO
+  foo/dir{~/b.+/}: x = 1
+
+  print $(foo/dir{bar}: x)
+  EOI
+  1
+  EOO
+
+  : invalid
+  :
+  $* <<EOI 2>>~/EOE/ != 0
+  file{~/'(.+'/}: x = 1
+  EOI
+  /<stdin>:1:1: error: invalid regex pattern .+/
+  EOE
+}