From 8bd89cfca333e58f6990d7d168649dfc79878f31 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Thu, 19 Feb 2015 16:10:03 +0200
Subject: Add support for sourcing/including buildfiles, print, dir{} alias

---
 build/b.cxx                                    |  10 +-
 build/context                                  |   9 +
 build/context.cxx                              |  15 +
 build/diagnostics                              |  23 +-
 build/parser                                   |  38 ++-
 build/parser.cxx                               | 434 +++++++++++++++++++------
 build/path                                     |  13 +
 build/rule                                     |  17 +-
 build/rule.cxx                                 |  36 +-
 build/target                                   |  14 +
 build/target.cxx                               |  16 +-
 tests/build/semantics/include/buildfile        |   1 +
 tests/build/semantics/include/includee1        |   1 +
 tests/build/semantics/include/includee2        |   1 +
 tests/build/semantics/include/includee4        |   1 +
 tests/build/semantics/include/includer         |   9 +
 tests/build/semantics/include/nested/includee3 |   2 +
 tests/build/semantics/include/nested/includee5 |   1 +
 tests/build/semantics/include/test.std         |   5 +
 tests/build/semantics/source/buildfile         |   1 +
 tests/build/semantics/source/nested/sourcee3   |   1 +
 tests/build/semantics/source/sourcee1          |   1 +
 tests/build/semantics/source/sourcee2          |   1 +
 tests/build/semantics/source/sourcer           |   8 +
 tests/build/semantics/source/test.std          |   5 +
 25 files changed, 542 insertions(+), 121 deletions(-)
 create mode 120000 tests/build/semantics/include/buildfile
 create mode 100644 tests/build/semantics/include/includee1
 create mode 100644 tests/build/semantics/include/includee2
 create mode 100644 tests/build/semantics/include/includee4
 create mode 100644 tests/build/semantics/include/includer
 create mode 100644 tests/build/semantics/include/nested/includee3
 create mode 100644 tests/build/semantics/include/nested/includee5
 create mode 100644 tests/build/semantics/include/test.std
 create mode 120000 tests/build/semantics/source/buildfile
 create mode 100644 tests/build/semantics/source/nested/sourcee3
 create mode 100644 tests/build/semantics/source/sourcee1
 create mode 100644 tests/build/semantics/source/sourcee2
 create mode 100644 tests/build/semantics/source/sourcer
 create mode 100644 tests/build/semantics/source/test.std

diff --git a/build/b.cxx b/build/b.cxx
index 3d19131..c9322a0 100644
--- a/build/b.cxx
+++ b/build/b.cxx
@@ -154,6 +154,7 @@ main (int argc, char* argv[])
     // Register target types.
     //
     target_types.insert (file::static_type);
+    target_types.insert (dir::static_type);
 
     target_types.insert (exe::static_type);
     target_types.insert (obj::static_type);
@@ -225,7 +226,7 @@ main (int argc, char* argv[])
     //
     path bf ("buildfile");
 
-    ifstream ifs (bf.string ().c_str ());
+    ifstream ifs (bf.string ());
     if (!ifs.is_open ())
       fail << "unable to open " << bf;
 
@@ -251,8 +252,11 @@ main (int argc, char* argv[])
     cxx::compile cxx_compile;
     rules[typeid (obj)].emplace ("cxx.gnu.compile", cxx_compile);
 
-    default_path_rule path_exists;
-    rules[typeid (path_target)].emplace ("", path_exists);
+    dir_rule dir_r;
+    rules[typeid (dir)].emplace ("", dir_r);
+
+    path_rule path_r;
+    rules[typeid (path_target)].emplace ("", path_r);
 
     // Build.
     //
diff --git a/build/context b/build/context
index a369ade..05f0094 100644
--- a/build/context
+++ b/build/context
@@ -21,6 +21,15 @@ namespace build
   extern path src_base;
   extern path out_base;
 
+  // Return the src/out directory corresponding to the given out/src. The
+  // passed directory should be a sub-directory of out/src_root.
+  //
+  path
+  src_out (const path&);
+
+  path
+  out_src (const path&);
+
   // If possible, translate an absolute, normalized path into relative to
   // the work directory.
   //
diff --git a/build/context.cxx b/build/context.cxx
index 2eb76c0..4d1d1e4 100644
--- a/build/context.cxx
+++ b/build/context.cxx
@@ -5,6 +5,7 @@
 #include <build/context>
 
 #include <ostream>
+#include <cassert>
 
 using namespace std;
 
@@ -20,6 +21,20 @@ namespace build
   path out_base;
 
   path
+  src_out (const path& o)
+  {
+    assert (o.sub (out_root));
+    return src_root / o.leaf (out_root);
+  }
+
+  path
+  out_src (const path& s)
+  {
+    assert (s.sub (src_root));
+    return out_root / s.leaf (src_root);
+  }
+
+  path
   translate (const path& p)
   {
     if (p.sub (work))
diff --git a/build/diagnostics b/build/diagnostics
index f85d118..7e56fa3 100644
--- a/build/diagnostics
+++ b/build/diagnostics
@@ -238,15 +238,17 @@ namespace build
   private:
     const char* type_;
     const char* name_;
-    const location& loc_;
+    const location loc_;
   };
   typedef diag_prologue<location_prologue_base> location_prologue;
 
   struct basic_mark_base
   {
     explicit
-    basic_mark_base (const char* type, const char* name = nullptr)
-        : type_ (type), name_ (name) {}
+    basic_mark_base (const char* type,
+                     const char* name = nullptr,
+                     const void* data = nullptr)
+        : type_ (type), name_ (name), data_ (data) {}
 
     simple_prologue
     operator() () const
@@ -264,12 +266,13 @@ namespace build
     location_prologue
     operator() (const L& l) const
     {
-      return location_prologue (type_, name_, get_location (l));
+      return location_prologue (type_, name_, get_location (l, data_));
     }
 
   private:
     const char* type_;
     const char* name_;
+    const void* data_;
   };
   typedef diag_mark<basic_mark_base> basic_mark;
 
@@ -281,7 +284,8 @@ namespace build
   struct trace_mark_base: basic_mark_base
   {
     explicit
-    trace_mark_base (const char* name): basic_mark_base ("trace", name) {}
+    trace_mark_base (const char* name, const void* data = nullptr)
+        : basic_mark_base ("trace", name, data) {}
   };
   typedef diag_mark<trace_mark_base> trace_mark;
 
@@ -290,6 +294,9 @@ namespace build
   template <typename E>
   struct fail_mark_base
   {
+    explicit
+    fail_mark_base (const void* data = nullptr): data_ (data) {}
+
     simple_prologue
     operator() () const
     {
@@ -306,11 +313,15 @@ namespace build
     location_prologue
     operator() (const L& l) const
     {
-      return location_prologue (&epilogue, "error", nullptr, get_location (l));
+      return location_prologue (
+        &epilogue, "error", nullptr, get_location (l, data_));
     }
 
     static void
     epilogue (const diag_record&) {throw E ();}
+
+  private:
+    const void* data_;
   };
 
   template <typename E>
diff --git a/build/parser b/build/parser
index 7515908..b62e8e7 100644
--- a/build/parser
+++ b/build/parser
@@ -8,22 +8,23 @@
 #include <string>
 #include <vector>
 #include <iosfwd>
-#include <utility>   // std::move
+#include <utility>       // std::move
+#include <unordered_set>
 
 #include <build/path>
+#include <build/token>
 #include <build/diagnostics>
 
 namespace build
 {
   class scope;
-
-  class token;
-  enum class token_type;
   class lexer;
 
   class parser
   {
   public:
+    parser (): fail (&path_) {}
+
     // Issues diagnostics and throws failed in case of an error.
     //
     void
@@ -47,6 +48,15 @@ namespace build
     void
     parse_clause (token&, token_type&);
 
+    void
+    parse_print (token&, token_type&);
+
+    void
+    parse_source (token&, token_type&);
+
+    void
+    parse_include (token&, token_type&);
+
     names
     parse_names (token& t, token_type& tt)
     {
@@ -65,23 +75,23 @@ namespace build
     token_type
     next (token&, token_type&);
 
+    token_type
+    peek ();
+
     // Diagnostics.
     //
   private:
-    struct fail_mark_base: build::fail_mark_base<failed>
-    {
-      location_prologue
-      operator() (const token&) const;
-
-      const path* path_;
-    };
-    typedef diag_mark<fail_mark_base> fail_mark;
+    const fail_mark<failed> fail;
 
   private:
-    fail_mark fail;
-
+    const std::string* path_; // Path processed by diagnostic_string().
     lexer* lexer_;
     scope* scope_;
+
+    token peek_ {token_type::eos, 0, 0};
+    bool peeked_ {false};
+
+    std::unordered_set<path> include_;
   };
 }
 
diff --git a/build/parser.cxx b/build/parser.cxx
index 696e2a3..1cb0684 100644
--- a/build/parser.cxx
+++ b/build/parser.cxx
@@ -5,6 +5,9 @@
 #include <build/parser>
 
 #include <memory>   // unique_ptr
+#include <fstream>
+#include <utility>  // move()
+#include <iostream>
 
 #include <build/token>
 #include <build/lexer>
@@ -13,6 +16,7 @@
 #include <build/target>
 #include <build/prerequisite>
 #include <build/diagnostics>
+#include <build/context>
 
 using namespace std;
 
@@ -23,14 +27,37 @@ namespace build
   ostream&
   operator<< (ostream&, const token&);
 
+  static location
+  get_location (const token&, const void*);
+
   typedef token_type type;
 
+  // Given a target or prerequisite name, figure out its type, taking
+  // into account extensions, trailing '/', or anything else that might
+  // be relevant.
+  //
+  static const char*
+  find_target_type (const string& n, const string* e)
+  {
+    // Empty name or a name ending with a directory separator
+    // signifies a directory.
+    //
+    if (n.empty () || path::traits::is_separator (n.back ()))
+      return "dir";
+
+    //@@ TODO: derive type from extension.
+    //
+    return "file";
+  }
+
   void parser::
   parse (istream& is, const path& p, scope& s)
   {
+    string ds (diagnostic_string (p));
+    path_ = &ds;
+
     lexer l (is, p.string ());
     lexer_ = &l;
-    fail.path_ = &p;
     scope_ = &s;
 
     token t (type::eos, 0, 0);
@@ -46,51 +73,141 @@ namespace build
   void parser::
   parse_clause (token& t, token_type& tt)
   {
-    tracer trace ("parser::parse_clause");
+    tracer trace ("parser::parse_clause", &path_);
 
     while (tt != type::eos)
     {
       // We always start with one or more names.
       //
-      if (tt != type::name && tt != type::lcbrace)
+      if (tt != type::name && tt != type::lcbrace && tt != type::colon)
         break; // Something else. Let our caller handle that.
 
-      names tns (parse_names (t, tt));
+      // See if this is one of the keywords.
+      //
+      if (tt == type::name)
+      {
+        const string& n (t.name ());
+
+        if (n == "print")
+        {
+          // @@ Is this the only place where it is valid? Probably also
+          // in var namespace.
+          //
+          next (t, tt);
+          parse_print (t, tt);
+          continue;
+        }
+        else if (n == "source")
+        {
+          next (t, tt);
+          parse_source (t, tt);
+          continue;
+        }
+        else if (n == "include")
+        {
+          next (t, tt);
+          parse_include (t, tt);
+          continue;
+        }
+      }
+
+      // ': foo' is equvalent to '{}: foo' and to 'dir{}: foo'.
+      //
+      names tns (tt != type::colon
+                 ? parse_names (t, tt)
+                 : names({name_type ("", path (), "")}));
 
       if (tt == type::colon)
       {
         next (t, tt);
 
-        // Dependency declaration.
-        //
-        if (tt == type::name || tt == type::lcbrace)
+        if (tt == type::newline)
         {
-          names pns (parse_names (t, tt));
-
-          // Prepare the prerequisite list.
+          // See if this is a directory/target scope.
           //
-          target::prerequisites_type ps;
-          ps.reserve (pns.size ());
-
-          for (auto& pn: pns)
+          if (peek () == type::lcbrace)
           {
-            // Resolve prerequisite type.
+            next (t, tt);
+
+            // Should be on its own line.
             //
-            //@@ TODO: derive type from extension, factor to common function
+            if (next (t, tt) != type::newline)
+              fail (t) << "expected newline after {";
+
+            // See if this is a directory or target scope. Different
+            // things can appear inside depending on which one it is.
             //
-            const char* tt (pn.type.empty () ? "file" : pn.type.c_str ());
+            bool dir (false);
+            for (const auto& n: tns)
+            {
+              if (n.type.empty () && n.name.back () == '/')
+              {
+                if (tns.size () != 1)
+                {
+                  // @@ TODO: point to name.
+                  //
+                  fail (t) << "multiple names in directory scope";
+                }
 
-            auto i (target_types.find (tt));
+                dir = true;
+              }
+            }
 
-            if (i == target_types.end ())
+            next (t, tt);
+
+            if (dir)
             {
-              //@@ TODO name (or better yet, type) location
+              scope& prev (*scope_);
+              path p (tns[0].name);
 
-              fail (t) << "unknown prerequisite type " << tt;
+              if (p.relative ())
+                p = prev.path () / p;
+
+              p.normalize ();
+              scope_ = &scopes[p];
+
+              // A directory scope can contain anything that a top level can.
+              //
+              parse_clause (t, tt);
+
+              scope_ = &prev;
+            }
+            else
+            {
+              // @@ TODO: target scope.
             }
 
-            const target_type& ti (i->second);
+            if (tt != type::rcbrace)
+              fail (t) << "expected '}' instead of " << t;
+
+            // Should be on its own line.
+            //
+            if (next (t, tt) == type::newline)
+              next (t, tt);
+            else if (tt != type::eos)
+              fail (t) << "expected newline after }";
 
+            continue;
+          }
+
+          // If this is not a scope, then it is a target without any
+          // prerequisites.
+          //
+        }
+
+        // Dependency declaration.
+        //
+        if (tt == type::name || tt == type::lcbrace || tt == type::newline)
+        {
+          names pns (tt != type::newline ? parse_names (t, tt) : names ());
+
+          // Prepare the prerequisite list.
+          //
+          target::prerequisites_type ps;
+          ps.reserve (pns.size ());
+
+          for (auto& pn: pns)
+          {
             // We need to split the path into its directory part (if any)
             // the name part, and the extension (if any). We cannot assume
             // the name part is a valid filesystem name so we will have
@@ -111,6 +228,16 @@ namespace build
                 n.assign (pn.name, i + 1, string::npos);
               }
 
+              // Handle '.' and '..'.
+              //
+              if (n == ".")
+                n.clear ();
+              else if (n == "..")
+              {
+                d /= path (n);
+                n.clear ();
+              }
+
               d.normalize ();
 
               // Extract extension.
@@ -124,6 +251,23 @@ namespace build
               }
             }
 
+            // Resolve prerequisite type.
+            //
+            const char* tt (pn.type.empty ()
+                            ? find_target_type (n, e)
+                            : pn.type.c_str ());
+
+            auto i (target_types.find (tt));
+
+            if (i == target_types.end ())
+            {
+              //@@ TODO name (or better yet, type) location
+
+              fail (t) << "unknown prerequisite type " << tt;
+            }
+
+            const target_type& ti (i->second);
+
             // Find or insert.
             //
             prerequisite& p (
@@ -152,6 +296,16 @@ namespace build
                 n.assign (tn.name, i + 1, string::npos);
               }
 
+              // Handle '.' and '..'.
+              //
+              if (n == ".")
+                n.clear ();
+              else if (n == "..")
+              {
+                d /= path (n);
+                n.clear ();
+              }
+
               if (d.empty ())
                 d = scope_->path (); // Already normalized.
               else
@@ -175,9 +329,9 @@ namespace build
 
             // Resolve target type.
             //
-            //@@ TODO: derive type from extension
-            //
-            const char* tt (tn.type.empty () ? "file" : tn.type.c_str ());
+            const char* tt (tn.type.empty ()
+                            ? find_target_type (n, e)
+                            : tn.type.c_str ());
 
             auto i (target_types.find (tt));
 
@@ -210,82 +364,155 @@ namespace build
           continue;
         }
 
-        if (tt == type::newline)
-        {
-          // See if we have a directory/target scope.
-          //
-          if (next (t, tt) == type::lcbrace)
-          {
-            // Should be on its own line.
-            //
-            if (next (t, tt) != type::newline)
-              fail (t) << "expected newline after {";
+        if (tt == type::eos)
+          continue;
 
-            // See if this is a directory or target scope. Different
-            // things can appear inside depending on which one it is.
-            //
-            bool dir (false);
-            for (const auto& n: tns)
-            {
-              if (n.type.empty () && n.name.back () == '/')
-              {
-                if (tns.size () != 1)
-                {
-                  // @@ TODO: point to name.
-                  //
-                  fail (t) << "multiple names in directory scope";
-                }
+        fail (t) << "expected newline instead of " << t;
+      }
 
-                dir = true;
-              }
-            }
+      fail (t) << "unexpected " << t;
+    }
+  }
 
-            next (t, tt);
+  void parser::
+  parse_source (token& t, token_type& tt)
+  {
+    tracer trace ("parser::parse_source", &path_);
 
-            if (dir)
-            {
-              scope& prev (*scope_);
-              path p (tns[0].name);
+    // The rest should be a list of paths to buildfiles.
+    //
+    for (; tt != type::newline && tt != type::eos; next (t, tt))
+    {
+      if (tt != type::name)
+        fail (t) << "expected buildfile to source instead of " << t;
 
-              if (p.relative ())
-                p = prev.path () / p;
+      path p (t.name ());
 
-              p.normalize ();
-              scope_ = &scopes[p];
+      // If the path is relative then use the src directory corresponding
+      // to the current directory scope.
+      //
+      if (p.relative ())
+        p = src_out (scope_->path ()) / p;
 
-              // A directory scope can contain anything that a top level can.
-              //
-              parse_clause (t, tt);
+      ifstream ifs (p.string ());
 
-              scope_ = &prev;
-            }
-            else
-            {
-              // @@ TODO: target scope.
-            }
+      if (!ifs.is_open ())
+        fail (t) << "unable to open " << p;
 
-            if (tt != type::rcbrace)
-              fail (t) << "expected '}' instead of " << t;
+      ifs.exceptions (ifstream::failbit | ifstream::badbit);
 
-            // Should be on its own line.
-            //
-            if (next (t, tt) == type::newline)
-              next (t, tt);
-            else if (tt != type::eos)
-              fail (t) << "expected newline after }";
-          }
+      level4 ([&]{trace (t) << "entering " << p;});
 
-          continue;
-        }
+      string ds (diagnostic_string (p));
+      const string* op (path_);
+      path_ = &ds;
 
-        if (tt == type::eos)
-          continue;
+      lexer l (ifs, p.string ());
+      lexer* ol (lexer_);
+      lexer_ = &l;
+
+      next (t, tt);
+      parse_clause (t, tt);
+
+      if (tt != type::eos)
+        fail (t) << "unexpected " << t;
+
+      level4 ([&]{trace (t) << "leaving " << p;});
+
+      lexer_ = ol;
+      path_ = op;
+    }
+
+    if (tt != type::eos)
+      next (t, tt); // Swallow newline.
+  }
+
+  void parser::
+  parse_include (token& t, token_type& tt)
+  {
+    tracer trace ("parser::parse_include", &path_);
+
+    // The rest should be a list of paths to buildfiles.
+    //
+    for (; tt != type::newline && tt != type::eos; next (t, tt))
+    {
+      if (tt != type::name)
+        fail (t) << "expected buildfile to include instead of " << t;
+
+      path p (t.name ());
+      bool in_out (false);
+
+      if (p.absolute ())
+      {
+        p.normalize ();
+
+        // Make sure the path is in this project. Include is only meant
+        // to be used for intra-project inclusion.
+        //
+        if (!p.sub (src_root) && !(in_out = p.sub (out_root)))
+          fail (t) << "out of project include " << p;
+      }
+      else
+      {
+        // Use the src directory corresponding to the current directory scope.
+        //
+        p = src_out (scope_->path ()) / p;
+        p.normalize ();
+      }
 
-        fail (t) << "expected newline insetad of " << t;
+      if (!include_.insert (p).second)
+      {
+        level4 ([&]{trace (t) << "skipping already included " << p;});
+        continue;
       }
 
-      fail (t) << "unexpected " << t;
+      ifstream ifs (p.string ());
+
+      if (!ifs.is_open ())
+        fail (t) << "unable to open " << p;
+
+      ifs.exceptions (ifstream::failbit | ifstream::badbit);
+
+      level4 ([&]{trace (t) << "entering " << p;});
+
+      string ds (diagnostic_string (p));
+      const string* op (path_);
+      path_ = &ds;
+
+      lexer l (ifs, p.string ());
+      lexer* ol (lexer_);
+      lexer_ = &l;
+
+      scope* os (scope_);
+      scope_ = &scopes[(in_out ? p : out_src (p)).directory ()];
+
+      next (t, tt);
+      parse_clause (t, tt);
+
+      if (tt != type::eos)
+        fail (t) << "unexpected " << t;
+
+      level4 ([&]{trace (t) << "leaving " << p;});
+
+      scope_ = os;
+      lexer_ = ol;
+      path_ = op;
     }
+
+    if (tt != type::eos)
+      next (t, tt); // Swallow newline.
+  }
+
+  void parser::
+  parse_print (token& t, token_type& tt)
+  {
+    for (; tt != type::newline && tt != type::eos; next (t, tt))
+      cout << t;
+
+    cout << endl;
+
+    if (tt != type::eos)
+      next (t, tt); // Swallow newline.
   }
 
   void parser::
@@ -372,23 +599,48 @@ namespace build
       if (!first)
         break;
 
-      fail (t) << "expected name instead of " << t;
+      if (tt == type::rcbrace) // Empty name, e.g., dir{}.
+      {
+        ns.emplace_back ((tp != nullptr ? *tp : string ()),
+                         (dp != nullptr ? *dp : path ()),
+                         "");
+        break;
+      }
+      else
+        fail (t) << "expected name instead of " << t;
     }
   }
 
   token_type parser::
   next (token& t, token_type& tt)
   {
-    t = lexer_->next ();
+    if (!peeked_)
+      t = lexer_->next ();
+    else
+    {
+      t = move (peek_);
+      peeked_ = false;
+    }
+
     tt = t.type ();
     return tt;
   }
 
-  location_prologue parser::fail_mark_base::
-  operator() (const token& t) const
+  token_type parser::
+  peek ()
+  {
+    if (!peeked_)
+      peek_ = lexer_->next ();
+
+    return peek_.type ();
+  }
+
+  static location
+  get_location (const token& t, const void* data)
   {
-    return build::fail_mark_base<failed>::operator() (
-      location (path_->string ().c_str (), t.line (), t.column ()));
+    assert (data != nullptr);
+    const string& p (**static_cast<const string* const*> (data));
+    return location (p.c_str (), t.line (), t.column ());
   }
 
   // Output the token type and value in a format suitable for diagnostics.
diff --git a/build/path b/build/path
index ee7937b..8eb560b 100644
--- a/build/path
+++ b/build/path
@@ -385,6 +385,19 @@ namespace build
   */
 }
 
+namespace std
+{
+  template <typename C>
+  struct hash<build::basic_path<C>>: hash<basic_string<C>>
+  {
+    size_t
+    operator() (const build::basic_path<C>& p) const
+    {
+      return hash<basic_string<C>>::operator() (p.string ());
+    }
+  };
+}
+
 #include <build/path.ixx>
 #include <build/path.txx>
 
diff --git a/build/rule b/build/rule
index 325204f..378ed9b 100644
--- a/build/rule
+++ b/build/rule
@@ -31,7 +31,22 @@ namespace build
 
   extern rule_map rules;
 
-  class default_path_rule: public rule
+  // Fallback rule that check that the path exists.
+  //
+  class path_rule: public rule
+  {
+  public:
+    virtual void*
+    match (target&, const std::string& hint) const;
+
+    virtual recipe
+    select (target&, void*) const;
+
+    static target_state
+    update (target&);
+  };
+
+  class dir_rule: public rule
   {
   public:
     virtual void*
diff --git a/build/rule.cxx b/build/rule.cxx
index d40eebf..e145ea8 100644
--- a/build/rule.cxx
+++ b/build/rule.cxx
@@ -14,9 +14,9 @@ namespace build
 {
   rule_map rules;
 
-  // default_path_rule
+  // path_rule
   //
-  void* default_path_rule::
+  void* path_rule::
   match (target& t, const string&) const
   {
     // @@ TODO:
@@ -51,13 +51,13 @@ namespace build
     return pt.mtime () != timestamp_nonexistent ? &t : nullptr;
   }
 
-  recipe default_path_rule::
+  recipe path_rule::
   select (target&, void*) const
   {
     return &update;
   }
 
-  target_state default_path_rule::
+  target_state path_rule::
   update (target& t)
   {
     // Make sure the target is not older than any of its prerequisites.
@@ -99,4 +99,32 @@ namespace build
 
     return target_state::uptodate;
   }
+
+  // dir_rule
+  //
+  void* dir_rule::
+  match (target& t, const string&) const
+  {
+    return &t;
+  }
+
+  recipe dir_rule::
+  select (target&, void*) const
+  {
+    return &update;
+  }
+
+  target_state dir_rule::
+  update (target& t)
+  {
+    for (const prerequisite& p: t.prerequisites)
+    {
+      auto ts (p.target->state ());
+
+      if (ts != target_state::uptodate)
+        return ts; // updated or failed
+    }
+
+    return target_state::uptodate;
+  }
 }
diff --git a/build/target b/build/target
index f57e8cc..b84931c 100644
--- a/build/target
+++ b/build/target
@@ -209,6 +209,20 @@ namespace build
     virtual const target_type& type () const {return static_type;}
     static const target_type static_type;
   };
+
+  // Directory alias/action target. Note that it is not mtime-based.
+  // Rather it is meant to represent a group of targets. For actual
+  // filesystem directory (creation), see fsdir.
+  //
+  class dir: public target
+  {
+  public:
+    using target::target;
+
+  public:
+    virtual const target_type& type () const {return static_type;}
+    static const target_type static_type;
+  };
 }
 
 #endif // BUILD_TARGET
diff --git a/build/target.cxx b/build/target.cxx
index 3852bc4..31a7f59 100644
--- a/build/target.cxx
+++ b/build/target.cxx
@@ -11,6 +11,11 @@ using namespace std;
 
 namespace build
 {
+  // target_type
+  //
+  const target_type*
+  resolve_target_type (const std::string name);
+
   // target
   //
   ostream&
@@ -23,7 +28,12 @@ namespace build
       string s (diagnostic_string (t.directory));
 
       if (!s.empty ())
-        os << s << path::traits::directory_separator;
+      {
+        os << s;
+
+        if (!t.name.empty ())
+          os << path::traits::directory_separator;
+      }
     }
 
     os << t.name;
@@ -79,7 +89,6 @@ namespace build
   }
 
   target_set targets;
-
   target* default_target = nullptr;
   target_type_map target_types;
 
@@ -103,4 +112,7 @@ namespace build
 
   const target_type file::static_type {
     typeid (file), "file", &path_target::static_type, &target_factory<file>};
+
+  const target_type dir::static_type {
+    typeid (dir), "dir", &target::static_type, &target_factory<dir>};
 }
diff --git a/tests/build/semantics/include/buildfile b/tests/build/semantics/include/buildfile
new file mode 120000
index 0000000..361dcf4
--- /dev/null
+++ b/tests/build/semantics/include/buildfile
@@ -0,0 +1 @@
+includer
\ No newline at end of file
diff --git a/tests/build/semantics/include/includee1 b/tests/build/semantics/include/includee1
new file mode 100644
index 0000000..70ed3fc
--- /dev/null
+++ b/tests/build/semantics/include/includee1
@@ -0,0 +1 @@
+print includee1
\ No newline at end of file
diff --git a/tests/build/semantics/include/includee2 b/tests/build/semantics/include/includee2
new file mode 100644
index 0000000..762825b
--- /dev/null
+++ b/tests/build/semantics/include/includee2
@@ -0,0 +1 @@
+print includee2
diff --git a/tests/build/semantics/include/includee4 b/tests/build/semantics/include/includee4
new file mode 100644
index 0000000..4964d81
--- /dev/null
+++ b/tests/build/semantics/include/includee4
@@ -0,0 +1 @@
+print includee4
diff --git a/tests/build/semantics/include/includer b/tests/build/semantics/include/includer
new file mode 100644
index 0000000..c129e33
--- /dev/null
+++ b/tests/build/semantics/include/includer
@@ -0,0 +1,9 @@
+include
+include includee1
+include includee1 ../include/includee2 # includee1 is skipped
+include nested/includee3
+nested/:
+{
+  include includee5
+  include ../includee2 # skipped
+}
diff --git a/tests/build/semantics/include/nested/includee3 b/tests/build/semantics/include/nested/includee3
new file mode 100644
index 0000000..7196e82
--- /dev/null
+++ b/tests/build/semantics/include/nested/includee3
@@ -0,0 +1,2 @@
+print nested/includee3
+include ../includee4
diff --git a/tests/build/semantics/include/nested/includee5 b/tests/build/semantics/include/nested/includee5
new file mode 100644
index 0000000..b4c9c74
--- /dev/null
+++ b/tests/build/semantics/include/nested/includee5
@@ -0,0 +1 @@
+print nested/includee5
diff --git a/tests/build/semantics/include/test.std b/tests/build/semantics/include/test.std
new file mode 100644
index 0000000..559584c
--- /dev/null
+++ b/tests/build/semantics/include/test.std
@@ -0,0 +1,5 @@
+includee1
+includee2
+nested/includee3
+includee4
+nested/includee5
diff --git a/tests/build/semantics/source/buildfile b/tests/build/semantics/source/buildfile
new file mode 120000
index 0000000..b6d1987
--- /dev/null
+++ b/tests/build/semantics/source/buildfile
@@ -0,0 +1 @@
+sourcer
\ No newline at end of file
diff --git a/tests/build/semantics/source/nested/sourcee3 b/tests/build/semantics/source/nested/sourcee3
new file mode 100644
index 0000000..cdf51fb
--- /dev/null
+++ b/tests/build/semantics/source/nested/sourcee3
@@ -0,0 +1 @@
+print nested/sourcee3
\ No newline at end of file
diff --git a/tests/build/semantics/source/sourcee1 b/tests/build/semantics/source/sourcee1
new file mode 100644
index 0000000..683cd1f
--- /dev/null
+++ b/tests/build/semantics/source/sourcee1
@@ -0,0 +1 @@
+print sourcee1
\ No newline at end of file
diff --git a/tests/build/semantics/source/sourcee2 b/tests/build/semantics/source/sourcee2
new file mode 100644
index 0000000..c989838
--- /dev/null
+++ b/tests/build/semantics/source/sourcee2
@@ -0,0 +1 @@
+print sourcee2
diff --git a/tests/build/semantics/source/sourcer b/tests/build/semantics/source/sourcer
new file mode 100644
index 0000000..e8b9558
--- /dev/null
+++ b/tests/build/semantics/source/sourcer
@@ -0,0 +1,8 @@
+source
+source sourcee1
+source sourcee1 ../source/sourcee2
+nested/:
+{
+  source sourcee3
+  source ../sourcee1
+}
diff --git a/tests/build/semantics/source/test.std b/tests/build/semantics/source/test.std
new file mode 100644
index 0000000..84d94b7
--- /dev/null
+++ b/tests/build/semantics/source/test.std
@@ -0,0 +1,5 @@
+sourcee1
+sourcee1
+sourcee2
+nested/sourcee3
+sourcee1
-- 
cgit v1.1