Add support for specifying minimum required build2 version

The syntax is:

using build@0.1.0-a1

The idea is that we will later also use it for modules and 'build' is
a special, the "build system itself" module.

Also fix a problem with peeking and lexer mode switching.

1 files changed, 13 insertions, 0 deletions

diff --git a/build/lexer.cxx b/build/lexer.cxx
index 79611c6..77e803c 100644
--- a/build/lexer.cxx
+++ b/build/lexer.cxx
@@ -17,6 +17,16 @@ namespace build
     return t;
   }
 
+  pair<char, bool> lexer::
+  peek_char ()
+  {
+    // In the quoted mode we don't skip spaces.
+    //
+    sep_ = mode_.top () != lexer_mode::quoted && skip_spaces ();
+    xchar c (peek ());
+    return make_pair (eos (c) ? '\0' : char (c), sep_);
+  }
+
   token lexer::
   next_impl ()
   {
@@ -385,6 +395,9 @@ namespace build
       get ();
     }
 
+    r = r || sep_;
+    sep_ = false;
+
     return r;
   }