From 728b075cb5e0df9c386f8377e0f6961e5ccc5143 Mon Sep 17 00:00:00 2001
From: Karen Arutyunov <karen@codesynthesis.com>
Date: Tue, 16 Jun 2020 17:08:39 +0300
Subject: Add env script pseudo-builtin

Also disable C++ recipe tests when cross-testing.
---
 doc/testscript.cli                                 |  30 ++-
 libbuild2/build/script/parser+diag.test.testscript |  36 +++
 libbuild2/build/script/parser.cxx                  |   6 +-
 libbuild2/build/script/parser.hxx                  |   9 +-
 libbuild2/script/parser.cxx                        | 162 ++++++++++++-
 libbuild2/script/parser.hxx                        |  14 +-
 libbuild2/script/run.cxx                           |  11 +-
 libbuild2/script/script.cxx                        | 130 +++++++++-
 libbuild2/script/script.hxx                        |   8 +-
 libbuild2/test/script/parser+env.test.testscript   |  77 ++++++
 tests/build/root.build                             |   1 -
 tests/recipe/cxx/testscript                        | 269 +++++++++++----------
 tests/test/script/runner/driver.cxx                |  25 +-
 tests/test/script/runner/env.testscript            |   7 +
 14 files changed, 618 insertions(+), 167 deletions(-)
 create mode 100644 libbuild2/test/script/parser+env.test.testscript
 create mode 100644 tests/test/script/runner/env.testscript

diff --git a/doc/testscript.cli b/doc/testscript.cli
index c0f0d4e..49725df 100644
--- a/doc/testscript.cli
+++ b/doc/testscript.cli
@@ -2426,6 +2426,34 @@ Write strings to \c{stdout} separating them with a single space and ending
 with a newline.
 
 
+\h#builtins-env|\c{env}|
+
+\
+env [-u <name>]... [-] [<name>=<value>]... -- <cmd>
+\
+
+Run a command adding/removing the variables to/from the environment.
+
+Note that \c{env} is a \i{pseudo-builtin}. In particular, its name and the
+\c{--} separator must be specified \i{literally} on the command line.
+Specifically, they must not be the result of an expansion. Also note that the
+\c{--} separator must always be present.
+
+To avoid ambiguity, the variable assignments can be separated from the options
+with the explicit \c{-} separator. In the example below the \c{--unset}
+variable is added to the environment:
+
+\
+env - --unset=FOO -- $*
+\
+
+\dl|
+
+\li|\n\c{-u|--unset <name>}
+
+  Remove the specified variable from the environment.||
+
+
 \h#builtins-exit|\c{exit}|
 
 \
@@ -2643,7 +2671,7 @@ is ECMAScript (more specifically, ECMA-262-based C++11 regular expressions).
 
   Edit \i{file} in place.|
 
-\li|\n\c{-e|--expression <script>}\n
+\li|\n\c{-e|--expression <script>}
 
   Editing commands to be executed (required).||
 
diff --git a/libbuild2/build/script/parser+diag.test.testscript b/libbuild2/build/script/parser+diag.test.testscript
index 60683bc..5b4e64a 100644
--- a/libbuild2/build/script/parser+diag.test.testscript
+++ b/libbuild2/build/script/parser+diag.test.testscript
@@ -55,3 +55,39 @@ $* <<EOI >>~%EOO%
       buildfile:12:1: info: previous call is here
     EOE
 }
+
+: inside-if
+:
+$* <<EOI 2>>EOE != 0
+  if true
+    diag copy >= $>
+  fi
+  EOI
+  buildfile:12:3: error: 'diag' call inside flow control construct
+  EOE
+
+: inside-if-cond
+:
+$* <<EOI 2>>EOE != 0
+  if diag copy >= $>
+    true
+  fi
+  EOI
+  buildfile:11:4: error: 'diag' call inside flow control construct
+  EOE
+
+: second-command
+:
+$* <<EOI 2>>EOE != 0
+  true && diag copy >= $>
+  EOI
+  buildfile:11:9: error: 'diag' call must be the only command
+  EOE
+
+: via-env
+:
+$* <<EOI 2>>EOE != 0
+  env -- diag copy >= $>
+  EOI
+  buildfile:11:8: error: 'diag' call via 'env' builtin
+  EOE
diff --git a/libbuild2/build/script/parser.cxx b/libbuild2/build/script/parser.cxx
index 2c41ac1..8f2c46d 100644
--- a/libbuild2/build/script/parser.cxx
+++ b/libbuild2/build/script/parser.cxx
@@ -330,6 +330,7 @@ namespace build2
       optional<process_path> parser::
       parse_program (token& t, build2::script::token_type& tt,
                      bool first,
+                     bool env,
                      names& ns)
       {
         const location l (get_location (t));
@@ -369,13 +370,16 @@ namespace build2
           // Verify that the special builtin is not called inside an improper
           // context (flow control construct or complex expression).
           //
-          auto verify = [first, &v, &l, this] ()
+          auto verify = [first, env, &v, &l, this] ()
           {
             if (level_ != 0)
               fail (l) << "'" << v << "' call inside flow control construct";
 
             if (!first)
               fail (l) << "'" << v << "' call must be the only command";
+
+            if (env)
+              fail (l) << "'" << v << "' call via 'env' builtin";
           };
 
           if (v == "diag")
diff --git a/libbuild2/build/script/parser.hxx b/libbuild2/build/script/parser.hxx
index 73bcd09..5ada8be 100644
--- a/libbuild2/build/script/parser.hxx
+++ b/libbuild2/build/script/parser.hxx
@@ -98,13 +98,16 @@ namespace build2
         //
         // During pre-parsing try to deduce the low-verbosity script
         // diagnostics name as a program/builtin name or obtain the custom
-        // low-verbosity diagnostics specified with the diag builtin. Note
-        // that the diag builtin can only appear at the beginning of the
-        // command line.
+        // low-verbosity diagnostics specified with the diag builtin. Also
+        // handle the depdb builtin calls.
+        //
+        // Note that the diag and depdb builtins can only appear at the
+        // beginning of the command line.
         //
         virtual optional<process_path>
         parse_program (token&, build2::script::token_type&,
                        bool first,
+                       bool env,
                        names&) override;
 
       protected:
diff --git a/libbuild2/script/parser.cxx b/libbuild2/script/parser.cxx
index a00651c..d5cff1a 100644
--- a/libbuild2/script/parser.cxx
+++ b/libbuild2/script/parser.cxx
@@ -97,7 +97,7 @@ namespace build2
     }
 
     optional<process_path> parser::
-    parse_program (token& t, type& tt, bool, names& ns)
+    parse_program (token& t, type& tt, bool, bool, names& ns)
     {
       parse_names (t, tt,
                    ns,
@@ -1019,6 +1019,18 @@ namespace build2
               }
             }
 
+            bool prog (p == pending::program_first ||
+                       p == pending::program_next);
+
+            // Check if this is the env pseudo-builtin.
+            //
+            bool env (false);
+            if (prog && tt == type::word && t.value == "env")
+            {
+              c.variables = parse_env_builtin (t, tt);
+              env = true;
+            }
+
             // Parse the next chunk as names to get expansion, etc. Note that
             // we do it in the chunking mode to detect whether anything in
             // each chunk is quoted. If we are waiting for the command
@@ -1033,10 +1045,10 @@ namespace build2
             //
             reset_quoted (t);
 
-            if (p == pending::program_first || p == pending::program_next)
+            if (prog)
             {
               optional<process_path> pp (
-                parse_program (t, tt, p == pending::program_first, ns));
+                parse_program (t, tt, p == pending::program_first, env, ns));
 
               // During pre-parsing we are not interested in the
               // parse_program() call result, so just discard the potentially
@@ -1088,7 +1100,7 @@ namespace build2
               {
                 diag_record dr (fail (l));
                 dr << "invalid string value ";
-                to_stream (dr.os, n, true); // Quote.
+                to_stream (dr.os, n, true /* quote */);
               }
 
               // If it is a quoted chunk, then we add the word as is.
@@ -1275,6 +1287,146 @@ namespace build2
       return make_pair (move (expr), move (hd));
     }
 
+    environment_vars parser::
+    parse_env_builtin (token& t, token_type& tt)
+    {
+      // enter: 'env' word token
+      // leave: first token of the program name
+
+      next (t, tt); // Skip 'env'.
+
+      // Note that the -u option and its value can belong to the different
+      // name chunks. That's why we parse the env builtin arguments in the
+      // chunking mode into the argument/location pair list up to the '--'
+      // separator and parse this list into the variable sets/unsets
+      // afterwords.
+      //
+      // Align the size with environment_vars (double because of -u <var>
+      // which is two arguments).
+      //
+      using args = small_vector<pair<string, location>, 4>;
+
+      args as;
+      names ns; // Reuse to reduce allocations.
+      while (tt != type::word || t.value != "--")
+      {
+        location l (get_location (t));
+
+        if (!start_names (tt))
+          fail (l) << "env: expected option, variable, or '--' separator "
+                   << "instead of " << t;
+
+        parse_names (t, tt,
+                     ns,
+                     pattern_mode::ignore,
+                     true /* chunk */,
+                     "env builtin argument",
+                     nullptr);
+
+        if (pre_parse_)
+          continue;
+
+        for (name& n: ns)
+        {
+          try
+          {
+            as.emplace_back (
+              value_traits<string>::convert (move (n), nullptr), l);
+          }
+          catch (const invalid_argument&)
+          {
+            diag_record dr (fail (l));
+            dr << "invalid string value ";
+            to_stream (dr.os, n, true /* quote */);
+          }
+        }
+
+        ns.clear ();
+      }
+
+      location l (get_location (t)); // '--' location.
+      next (t, tt);                  // Skip '--'.
+
+      if (tt == type::newline || tt == type::eos)
+        fail (t) << "env: expected program name instead of " << t;
+
+      // Parse the env builtin options and arguments.
+      //
+      environment_vars r;
+
+      // Note: args is empty in the pre-parse mode.
+      //
+      auto i (as.begin ()), e (as.end ());
+
+      // Parse the variable unsets (from options).
+      //
+      for (; i != e; ++i)
+      {
+        string& o (i->first);
+
+        // Bail out if the options and arguments separator is encountered.
+        //
+        if (o == "-")
+        {
+          ++i;
+          break;
+        }
+
+        // Unset the variable, adding its name to the resulting variable list.
+        //
+        auto unset = [&r, &i, this] (string&& v, const char* o)
+        {
+          if (v.empty ())
+            fail (i->second) << "env: empty value for option '" << o << "'";
+
+          if (v.find ('=') != string::npos)
+            fail (i->second) << "env: invalid value '" << v << "' for "
+                             << "option '" << o << "': contains '='";
+
+          r.push_back (move (v));
+        };
+
+        // If this is the --unset|-u option then add the variable unset and
+        // bail out to parsing the variable sets otherwise.
+        //
+        if (o == "--unset" || o == "-u")
+        {
+          if (++i == e)
+            fail (l) << "env: missing value for option '" << o << "'";
+
+          unset (move (i->first), o.c_str ());
+        }
+        else if (o.compare (0, 8, "--unset=") == 0)
+          unset (string (o, 8), "--unset");
+        else
+          break;
+      }
+
+      // Parse the variable sets (from arguments).
+      //
+      for (; i != e; ++i)
+      {
+        string& a (i->first);
+
+        // Validate the variable assignment.
+        //
+        size_t p (a.find ('='));
+
+        if (p == string::npos)
+          fail (i->second)
+            << "env: expected variable assignment instead of '" << a << "'";
+
+        if (p == 0)
+          fail (i->second) << "env: empty variable name";
+
+        // Add the variable set to the resulting list.
+        //
+        r.push_back (move (a));
+      }
+
+      return r;
+    }
+
     command_exit parser::
     parse_command_exit (token& t, type& tt)
     {
@@ -1310,7 +1462,7 @@ namespace build2
           diag_record dr;
 
           dr << fail (l) << "expected exit status instead of ";
-          to_stream (dr.os, ns, true); // Quote.
+          to_stream (dr.os, ns, true /* quote */);
 
           dr << info << "exit status is an unsigned integer less than 256";
         }
diff --git a/libbuild2/script/parser.hxx b/libbuild2/script/parser.hxx
index bec6867..da69591 100644
--- a/libbuild2/script/parser.hxx
+++ b/libbuild2/script/parser.hxx
@@ -129,6 +129,15 @@ namespace build2
       line_type
       pre_parse_line_start (token&, token_type&, lexer_mode);
 
+      // Parse the env pseudo-builtin arguments up to the program name. Return
+      // the list of the variables that should be unset ("name") and/or set
+      // ("name=value") in the command environment and the token/type that
+      // starts the program name. Note that the variable unsets come first, if
+      // present.
+      //
+      environment_vars
+      parse_env_builtin (token&, token_type&);
+
       // Execute.
       //
     protected:
@@ -166,7 +175,8 @@ namespace build2
       //
     protected:
       // Parse the command's leading name chunk. The argument first is true if
-      // this is the first command in the line.
+      // this is the first command in the line. The argument env is true if
+      // the command is executed via the env pseudo-builtin.
       //
       // During the execution phase try to parse and translate the leading
       // names into the process path and return nullopt if choose not to do
@@ -189,7 +199,7 @@ namespace build2
       // recognize and execute certain directives, or some such.
       //
       virtual optional<process_path>
-      parse_program (token&, token_type&, bool first, names&);
+      parse_program (token&, token_type&, bool first, bool env, names&);
 
       // Set lexer pointers for both the current and the base classes.
       //
diff --git a/libbuild2/script/run.cxx b/libbuild2/script/run.cxx
index 46c061c..b90ba48 100644
--- a/libbuild2/script/run.cxx
+++ b/libbuild2/script/run.cxx
@@ -1619,16 +1619,19 @@ namespace build2
                            ? process::path_search (args[0])
                            : process_path ());
 
-          // Note: the builtin-escaping character '^' is not printed.
+          // Note that CWD and builtin-escaping character '^' are not printed.
           //
+          process_env pe (resolve ? pp : c.program, c.variables);
+
           if (verb >= 2)
-            print_process (args);
+            print_process (pe, args);
 
           process pr (
-            resolve ? pp : c.program,
+            *pe.path,
             args.data (),
             {ifd.get (), -1}, process::pipe (ofd), {-1, efd.get ()},
-            env.work_dir.path->string ().c_str ());
+            env.work_dir.path->string ().c_str (),
+            pe.vars);
 
           ifd.reset ();
           ofd.out.reset ();
diff --git a/libbuild2/script/script.cxx b/libbuild2/script/script.cxx
index d0d3304..ee238cc 100644
--- a/libbuild2/script/script.cxx
+++ b/libbuild2/script/script.cxx
@@ -229,22 +229,57 @@ namespace build2
       }
     }
 
-    // Quote if empty or contains spaces or any of the special characters.
-    // Note that we use single quotes since double quotes still allow
-    // expansion.
+    // Quote a string unconditionally, assuming it contains some special
+    // characters.
     //
-    // @@ What if it contains single quotes?
+    // If the quote character is present in the string then it is double
+    // quoted rather than single quoted. In this case the following characters
+    // are escaped:
+    //
+    // \"
+    //
+    static void
+    to_stream_quoted (ostream& o, const char* s)
+    {
+      if (strchr (s, '\'') != nullptr)
+      {
+        o << '"';
+
+        for (; *s != '\0'; ++s)
+        {
+          // Escape characters special inside double quotes.
+          //
+          if (strchr ("\\\"", *s) != nullptr)
+            o << '\\';
+
+          o << *s;
+        }
+
+        o << '"';
+      }
+      else
+        o << '\'' << s << '\'';
+    }
+
+    static inline void
+    to_stream_quoted (ostream& o, const string& s)
+    {
+      to_stream_quoted (o, s.c_str ());
+    }
+
+    // Quote if empty or contains spaces or any of the command line special
+    // characters.
     //
     static void
     to_stream_q (ostream& o, const string& s)
     {
       // NOTE: update dump(line) if adding any new special character.
       //
-      if (s.empty () || s.find_first_of (" |&<>=\\\"") != string::npos)
-        o << '\'' << s << '\'';
+      if (s.empty () || s.find_first_of (" |&<>=\\\"'") != string::npos)
+        to_stream_quoted (o, s);
       else
         o << s;
-    };
+    }
 
     void
     to_stream (ostream& o, const command& c, command_to_stream m)
@@ -373,6 +408,87 @@ namespace build2
 
       if ((m & command_to_stream::header) == command_to_stream::header)
       {
+        // Print the env builtin arguments, if any environment variable
+        // (un)sets are present.
+        //
+        if (!c.variables.empty ())
+        {
+          o << "env";
+
+          auto b (c.variables.begin ()), i (b), e (c.variables.end ());
+
+          // Print a variable name or assignment to the stream, quoting it if
+          // necessary.
+          //
+          auto print = [&o] (const string& v, bool name)
+          {
+            size_t p (v.find_first_of (" \\\"'"));
+
+            // Print the variable name/assignment as is if it doesn't contain
+            // any special characters.
+            //
+            if (p == string::npos)
+            {
+              o << v;
+              return;
+            }
+
+            // If the variable name contains any special characters, then
+            // quote the name/assignment as a whole.
+            //
+            size_t eq;
+            if (name || (eq = v.find ('=')) > p)
+            {
+              to_stream_quoted (o, v);
+              return;
+            }
+
+            // Finally, if the variable value contains any special characters,
+            // then we quote only the value.
+            //
+            assert (eq != string::npos);
+
+            o.write (v.c_str (), eq + 1);              // Includes '='.
+            to_stream_quoted (o, v.c_str () + eq + 1);
+          };
+
+          // Variable unsets.
+          //
+          // Print the variable unsets as the -u options until a variable set
+          // is encountered (contains '=') or the end of the variable list is
+          // reached. In the former case, to avoid a potential ambiguity add
+          // the '-' separator, if there are any options.
+          //
+          // Note that we rely on the fact that unsets come first, which is
+          // guaranteed by parser::parse_env_builtin().
+          //
+          for (; i != e; ++i)
+          {
+            const string& v (*i);
+
+            if (v.find ('=') == string::npos) // Variable unset.
+            {
+              o << " -u "; print (v, true /* name*/);
+            }
+            else                              // Variable set.
+            {
+              if (i != b)
+                o << " -";
+
+              break;
+            }
+          }
+
+          // Variable sets.
+          //
+          for (; i != e; ++i)
+          {
+            o << ' '; print (*i, false /* name */);
+          }
+
+          o << " -- ";
+        }
+
         // Program.
         //
         to_stream_q (o, c.program.recall_string ());
diff --git a/libbuild2/script/script.hxx b/libbuild2/script/script.hxx
index d751169..8e1c852 100644
--- a/libbuild2/script/script.hxx
+++ b/libbuild2/script/script.hxx
@@ -298,6 +298,11 @@ namespace build2
 
     // command
     //
+    // Align with butl::process_env, assuming it is not very common to (un)set
+    // more than two variables.
+    //
+    using environment_vars = small_vector<string, 2>;
+
     struct command
     {
       // We use NULL initial as an indication that the path stored in recall
@@ -306,7 +311,8 @@ namespace build2
       //
       process_path program;
 
-      strings arguments;
+      strings          arguments;
+      environment_vars variables;
 
       optional<redirect> in;
       optional<redirect> out;
diff --git a/libbuild2/test/script/parser+env.test.testscript b/libbuild2/test/script/parser+env.test.testscript
new file mode 100644
index 0000000..b1e864c
--- /dev/null
+++ b/libbuild2/test/script/parser+env.test.testscript
@@ -0,0 +1,77 @@
+# file      : libbuild2/test/script/parser+env.test.testscript
+# license   : MIT; see accompanying LICENSE file
+
+: unset
+:
+{
+  $* <'env -u a -- cmd'      >'env -u a -- cmd'      : short-opt
+  $* <'env --unset a -- cmd' >'env -u a -- cmd'      : long-opt
+  $* <'env --unset=a -- cmd' >'env -u a -- cmd'      : long-opt-eq
+  $* <'env -u a -u b -- cmd' >'env -u a -u b -- cmd' : mult-opt
+  $* <'env -u "a b" -- cmd'  >"env -u 'a b' -- cmd"  : quote
+
+  : invalid-opt
+  :
+  $* <'env -w a -- cmd' 2>>EOE != 0
+    testscript:1:5: error: env: expected variable assignment instead of '-w'
+    EOE
+
+  : no-val
+  :
+  $* <'env -u -- cmd' 2>>EOE != 0
+    testscript:1:8: error: env: missing value for option '-u'
+    EOE
+
+  : empty-val
+  :
+  $* <'env --unset= -- cmd' 2>>EOE != 0
+    testscript:1:5: error: env: empty value for option '--unset'
+    EOE
+
+  : invalid-val
+  :
+  $* <'env --unset=a=b -- cmd' 2>>EOE != 0
+    testscript:1:5: error: env: invalid value 'a=b' for option '--unset': contains '='
+    EOE
+
+  : no-sep
+  :
+  $* <'env -u a cmd' 2>>EOE != 0
+    testscript:1:13: error: env: expected option, variable, or '--' separator instead of <newline>
+    EOE
+
+  $* <'env && cmd' 2>>EOE != 0
+    testscript:1:5: error: env: expected option, variable, or '--' separator instead of '&&'
+    EOE
+}
+
+: set
+:
+{
+  $* <'env a=b -- cmd'      >'env a=b -- cmd'        : var
+  $* <'env -u a b=c -- cmd' >'env -u a - b=c -- cmd' : opt-var
+  $* <'env a="b c" -- cmd'  >"env a='b c' -- cmd"    : quote
+  $* <'env "a b"=c -- cmd'  >"env 'a b=c' -- cmd"    : quote-name
+
+  : double-quote
+  :
+  $* <<EOF >>EOF
+    env a="'a\"'" -- cmd
+    EOF
+
+  : expected-assign
+  :
+  $* <'env a -- cmd' 2>>EOE != 0
+    testscript:1:5: error: env: expected variable assignment instead of 'a'
+    EOE
+}
+
+: non-first
+:
+$* <'cmd1 && env -u a b=c -- cmd2' >'cmd1 && env -u a - b=c -- cmd2'
+
+: no-cmd
+:
+$* <'env -u a --' 2>>EOE != 0
+  testscript:1:12: error: env: expected program name instead of <newline>
+  EOE
diff --git a/tests/build/root.build b/tests/build/root.build
index e3f0f61..5bf6731 100644
--- a/tests/build/root.build
+++ b/tests/build/root.build
@@ -22,7 +22,6 @@ import.build2 = [null]
 import! [metadata] b = build2%exe{b}
 
 static = $($b:b.static) # True if testing statically-linked build system.
-shared = (!$static)     # For '$shared || exit' idiom.
 
 testscript{*}: test = $b
 
diff --git a/tests/recipe/cxx/testscript b/tests/recipe/cxx/testscript
index 6601c0a..6b11c0f 100644
--- a/tests/recipe/cxx/testscript
+++ b/tests/recipe/cxx/testscript
@@ -1,168 +1,169 @@
 # file      : tests/recipe/cxx/testscript
 # license   : MIT; see accompanying LICENSE file
 
-# Ad hoc C++ recipes not supported in a statically-linked build system.
+# Ad hoc C++ recipes not supported in a statically-linked build system. Also
+# disable when cross-testing for the sake of simplicity.
 #
-+$shared || exit
-
-+mkdir build
-+cat <<EOI >=build/bootstrap.build
-  project = test
-  amalgamation =
-  subprojects =
-
-  using config
-  using test
-  EOI
-
-+cat <<EOI >=build/root.build
-  EOI
-
-+cat <<EOI >=buildfile
-  ./:
-  {{ c++ 1
-    // Dummy recipe to trigger cleanup.
-  }}
-  EOI
-
-: update-clean
-:
+if (!$static && $test.target == $build.host)
 {
-  echo 'bar' >=bar;
+  +mkdir build
+  +cat <<EOI >=build/bootstrap.build
+    project = test
+    amalgamation =
+    subprojects =
+
+    using config
+    using test
+    EOI
 
-  cat <<EOI >=buildfile;
-    foo: bar
-    % update clean
-    {{ c++ 1
-      recipe
-      apply (action a, target& xt) const override
-      {
-        file& t (xt.as<file> ());
+  +cat <<EOI >=build/root.build
+    EOI
 
-        t.derive_path ();
-        inject_fsdir (a, t);
-        match_prerequisite_members (a, t);
+  +cat <<EOI >=buildfile
+    ./:
+    {{ c++ 1
+      // Dummy recipe to trigger cleanup.
+    }}
+    EOI
 
-        switch (a)
+  : update-clean
+  :
+  {
+    echo 'bar' >=bar;
+
+    cat <<EOI >=buildfile;
+      foo: bar
+      % update clean
+      {{ c++ 1
+        recipe
+        apply (action a, target& xt) const override
         {
-        case perform_update_id:  return perform_update;
-        case perform_clean_id:   return perform_clean_depdb;
-        default: assert (false); return noop_recipe;
+          file& t (xt.as<file> ());
+
+          t.derive_path ();
+          inject_fsdir (a, t);
+          match_prerequisite_members (a, t);
+
+          switch (a)
+          {
+          case perform_update_id:  return perform_update;
+          case perform_clean_id:   return perform_clean_depdb;
+          default: assert (false); return noop_recipe;
+          }
         }
-      }
 
-      static target_state
-      perform_update (action a, const target& xt)
-      {
-        const file& t (xt.as<file> ());
-        const path& tp (t.path ());
+        static target_state
+        perform_update (action a, const target& xt)
+        {
+          const file& t (xt.as<file> ());
+          const path& tp (t.path ());
 
-        timestamp mt (t.load_mtime ());
-        auto pr (execute_prerequisites<file> (a, t, mt));
+          timestamp mt (t.load_mtime ());
+          auto pr (execute_prerequisites<file> (a, t, mt));
 
-        bool update (!pr.first);
-        target_state r (update ? target_state::changed : *pr.first);
+          bool update (!pr.first);
+          target_state r (update ? target_state::changed : *pr.first);
 
-        const file& s (pr.second);
-        const path& sp (s.path ());
+          const file& s (pr.second);
+          const path& sp (s.path ());
 
-        depdb dd (tp + ".d");
-        dd.expect (sp);
+          depdb dd (tp + ".d");
+          dd.expect (sp);
 
-        if (dd.writing () || dd.mtime > mt)
-          update = true;
+          if (dd.writing () || dd.mtime > mt)
+            update = true;
 
-        dd.close ();
+          dd.close ();
 
-        if (!update)
-          return r;
+          if (!update)
+            return r;
 
-        if (verb == 1)
-          text << "cp " << t;
-        else if (verb >= 2)
-          text << "cp " << sp << ' ' << tp;
+          if (verb == 1)
+            text << "cp " << t;
+          else if (verb >= 2)
+            text << "cp " << sp << ' ' << tp;
 
-        cpfile (sp, tp);
-        return target_state::changed;
-      }
-    }}
-    EOI
+          cpfile (sp, tp);
+          return target_state::changed;
+        }
+      }}
+      EOI
 
-  $* 2>>~%EOE%;
-    %^(c\+\+|ld).*%+
-    cp file{foo}
-    EOE
+    env BDEP_SYNC=0 -- $* 2>>~%EOE%;
+      %^(c\+\+|ld).*%+
+      cp file{foo}
+      EOE
 
-  cat <<<foo >'bar';
+    cat <<<foo >'bar';
 
-  # While at it, make sure there is no rebuild.
-  #
-  $* 2>/'info: dir{./} is up to date';
+    # While at it, make sure there is no rebuild.
+    #
+    env BDEP_SYNC=0 -- $* 2>/'info: dir{./} is up to date';
 
-  $* clean 2>-
-}
+    env BDEP_SYNC=0 -- $* clean 2>-
+  }
 
-#\
-@@ TMP disabled: env BDEP_SYNC=0
-: test
-:
-{
-  echo 'bar' >=bar;
+  : test
+  :
+  {
+    echo 'bar' >=bar;
 
-  cat <<EOI >=buildfile;
-    foo: bar
-    {{
-      cp $path($<) $path($>)
-    }}
-    % test
-    {{ c++ 1 --
+    cat <<EOI >=buildfile;
+      foo: bar
+      {{
+        cp $path($<) $path($>)
+      }}
+      % test
+      {{ c++ 1 --
 
-      #include <iostream>
+        #include <iostream>
 
-      --
+        --
 
-      recipe
-      apply (action a, target& t) const override
-      {
-        if (a.outer ())
+        recipe
+        apply (action a, target& t) const override
         {
-          match_inner (a, t);
-          return execute_inner;
+          if (a.outer ())
+          {
+            match_inner (a, t);
+            return execute_inner;
+          }
+          else
+            return perform_test;
         }
-        else
-          return perform_test;
-      }
-
-      static target_state
-      perform_test (action, const target& xt)
-      {
-        const file& t (xt.as<file> ());
-        const path& tp (t.path ());
-
-        if (verb == 1)
-          text << "test " << t;
-        else if (verb >= 2)
-          text << "cat " << tp;
-
-        ifdstream ifs (tp);
-        if (ifs.peek () != ifdstream::traits_type::eof ())
-          std::cerr << ifs.rdbuf ();
-        ifs.close ();
-
-        return target_state::changed;
-      }
-    }}
-    EOI
 
-  $* test 2>>~%EOE%;
-    %^(c\+\+|ld).*%+
-    cp file{foo}
-    test file{foo}
-    bar
-    EOE
+        static target_state
+        perform_test (action, const target& xt)
+        {
+          const file& t (xt.as<file> ());
+          const path& tp (t.path ());
 
-  $* clean 2>-
-}
-#\
+          if (verb == 1)
+            text << "test " << t;
+          else if (verb >= 2)
+            text << "cat " << tp;
+
+          ifdstream ifs (tp);
+          if (ifs.peek () != ifdstream::traits_type::eof ())
+            std::cerr << ifs.rdbuf ();
+          ifs.close ();
 
--$* clean 2>- # Clean recipe builds.
+          return target_state::changed;
+        }
+      }}
+      EOI
+
+    env BDEP_SYNC=0 -- $* test 2>>~%EOE%;
+      %^(c\+\+|ld).*%+
+      cp file{foo}
+      test file{foo}
+      bar
+      EOE
+
+    env BDEP_SYNC=0 -- $* clean 2>-
+  }
+
+  # Clean recipe builds if the testscript is enabled (see above for details).
+  #
+  -$* clean 2>-
+}
diff --git a/tests/test/script/runner/driver.cxx b/tests/test/script/runner/driver.cxx
index 08d5bba..d5a74a4 100644
--- a/tests/test/script/runner/driver.cxx
+++ b/tests/test/script/runner/driver.cxx
@@ -34,22 +34,22 @@ main (int argc, char* argv[])
   using butl::optional;
 
   // Usage: driver [-i <int>] (-o <string>)* (-e <string>)* (-f <file>)*
-  //        (-d <dir>)* [(-t (a|m|s|z)) | (-s <int>)]
+  //        (-d <dir>)* (-v <name>)* [(-t (a|m|s|z)) | (-s <int>)]
   //
-  // Execute actions specified by -i, -o, -e, -f, -d options in the order as
-  // they appear on the command line. After that terminate abnormally if -t
-  // option is provided, otherwise exit normally with the status specified by
-  // -s option (0 by default).
+  // Execute actions specified by -i, -o, -e, -f, -d, and -v options in the
+  // order as they appear on the command line. After that terminate abnormally
+  // if -t option is provided, otherwise exit normally with the status
+  // specified by -s option (0 by default).
   //
   // -i <fd>
-  //    Forward STDIN data to the standard stream denoted by the file
+  //    Forward stdin data to the standard stream denoted by the file
   //    descriptor. Read and discard if 0.
   //
   // -o <string>
-  //    Print the line to STDOUT.
+  //    Print the line to stdout.
   //
   // -e <string>
-  //    Print the line to STDERR.
+  //    Print the line to stderr.
   //
   // -f <path>
   //    Create an empty file with the path specified.
@@ -58,6 +58,10 @@ main (int argc, char* argv[])
   //    Create a directory with the path specified. Create parent directories
   //    if required.
   //
+  // -v <name>
+  //    If the specified variable is set the print its value to stdout and the
+  //    string '<none>' otherwise.
+  //
   // -t <method>
   //    Abnormally terminate itself using one of the following methods:
   //
@@ -135,6 +139,11 @@ main (int argc, char* argv[])
     {
       try_mkdir_p (dir_path (v));
     }
+    else if (o == "-v")
+    {
+      optional<string> var (getenv (v));
+      cout << (var ? *var : "<none>") << endl;
+    }
     else if (o == "-t")
     {
       assert (aterm == '\0' && !status); // Make sure exit method is not set.
diff --git a/tests/test/script/runner/env.testscript b/tests/test/script/runner/env.testscript
new file mode 100644
index 0000000..6fcedfa
--- /dev/null
+++ b/tests/test/script/runner/env.testscript
@@ -0,0 +1,7 @@
+# file      : tests/test/script/runner/env.testscript
+# license   : MIT; see accompanying LICENSE file
+
+.include ../common.testscript
+
+$c <'env abc=xyz -- $* -v abc >xyz' && $b                         : set
+$c <'env --unset=abc -- $* -v abc >"<none>"' && env abc=xyz -- $b : unset
-- 
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