Add in.substitution={strict|lax}

In the strict mode every substitution symbol is expected to start a
substitution with the double symbol (e.g., $$) serving as an
escape sequence.

In the lax mode a pair of substitution symbols is only treated as a
substitution if what's between them looks like a build2 variable
name (i.e., doesn't contain spaces, etc). Everything else,
including unterminated substitution symbols is copied as is. Note
also that in this mode the double symbol is not treated as an
escape sequence.

The lax mode is mostly useful when trying to reuse existing .in
files, for example from autoconf. Note, however, that the lax mode
is still stricter than the autoconf's semantics which also leaves
unknown substitutions as is.

1 files changed, 2 insertions, 1 deletions

diff --git a/build2/version/module.hxx b/build2/version/module.hxx
index 4f9f66d..190d8d7 100644
--- a/build2/version/module.hxx
+++ b/build2/version/module.hxx
@@ -27,7 +27,8 @@ namespace build2
       butl::standard_version version;
       dependency_constraints dependencies;
 
-      const variable* in_symbol = nullptr;
+      const variable* in_symbol       = nullptr; // in.symbol
+      const variable* in_substitution = nullptr; // in.substitution
 
       module (butl::standard_version v, dependency_constraints d)
           : version (move (v)), dependencies (move (d)) {}