Add support for value subscript after expansions

Value subscript is only recognized in evaluation contexts (due to ambiguity
with wildcard patterns; consider: $x[123].txt) and should be unseparated from
the previous token. For example:

x = ($y[1])
x = (($f ? $y : $z)[1])
x = ($identity($y)[$z])

1 files changed, 7 insertions, 8 deletions

diff --git a/libbuild2/test/script/lexer.cxx b/libbuild2/test/script/lexer.cxx
index a94109b..e895d4a 100644
--- a/libbuild2/test/script/lexer.cxx
+++ b/libbuild2/test/script/lexer.cxx
@@ -26,8 +26,6 @@ namespace build2
       void lexer::
       mode (base_mode m, char ps, optional<const char*> esc, uintptr_t data)
       {
-        bool a (false); // attributes
-
         const char* s1 (nullptr);
         const char* s2 (nullptr);
 
@@ -109,7 +107,8 @@ namespace build2
         }
 
         assert (ps == '\0');
-        state_.push (state {m, data, nullopt, a, ps, s, n, q, *esc, s1, s2});
+        state_.push (
+          state {m, data, nullopt, false, false, ps, s, n, q, *esc, s1, s2});
       }
 
       token lexer::
@@ -153,16 +152,16 @@ namespace build2
           return token (t, sep, ln, cn, token_printer);
         };
 
-        // Handle attributes (do it first to make sure the flag is cleared
-        // regardless of what we return).
+        // Handle `[` (do it first to make sure the flag is cleared regardless
+        // of what we return).
         //
-        if (st.attributes)
+        if (st.lsbrace)
         {
           assert (m == lexer_mode::variable_line);
 
-          state_.top ().attributes = false;
+          state_.top ().lsbrace = false; // Note: st is a copy.
 
-          if (c == '[')
+          if (c == '[' && (!st.lsbrace_unsep || !sep))
             return make_token (type::lsbrace);
         }