Implement in module

Given test.in containing something along these lines:

foo = $foo$

Now we can do:

using in

file{test}: in{test.in}
file{test}: foo = FOO

The alternative variable substitution symbol can be specified with the
in.symbol variable and lax (instead of the default strict) mode with
in.substitution. For example:

file{test}: in.symbol = '@'
file{test}: in.substitution = lax

1 files changed, 50 insertions, 0 deletions

diff --git a/build2/in/rule.hxx b/build2/in/rule.hxx
new file mode 100644
index 0000000..e588fd9f
--- /dev/null
+++ b/build2/in/rule.hxx
@@ -0,0 +1,50 @@
+// file      : build2/in/rule.hxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2018 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef BUILD2_IN_RULE_HXX
+#define BUILD2_IN_RULE_HXX
+
+#include <build2/types.hxx>
+#include <build2/utility.hxx>
+
+#include <build2/rule.hxx>
+
+namespace build2
+{
+  namespace in
+  {
+    // Preprocess an .in file.
+    //
+    class rule: public build2::rule
+    {
+    public:
+      rule () {}
+
+      virtual bool
+      match (action, target&, const string&) const override;
+
+      virtual recipe
+      apply (action, target&) const override;
+
+      // Perform variable lookup.
+      //
+      virtual string
+      lookup (const location&, const target&, const string& name) const;
+
+      // Perform variable substitution. Return nullopt if it should be
+      // ignored.
+      //
+      virtual optional<string>
+      substitute (const location&,
+                  const target&,
+                  const string& name,
+                  bool strict) const;
+
+      target_state
+      perform_update (action, const target&) const;
+    };
+  }
+}
+
+#endif // BUILD2_IN_RULE_HXX