From 6b9699f0f2e48961af25843eea9b694d043bd352 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Mon, 30 Sep 2019 12:53:29 +0200
Subject: Reserve `:` in `case` pattern expression for future match extraction
 support

---
 libbuild2/lexer.cxx     | 11 ++++++-----
 libbuild2/lexer.hxx     |  2 +-
 libbuild2/parser.cxx    | 12 +++++++++++-
 tests/switch/testscript | 12 ++++++++++++
 4 files changed, 30 insertions(+), 7 deletions(-)

diff --git a/libbuild2/lexer.cxx b/libbuild2/lexer.cxx
index 17b0c7d..61d7fbf 100644
--- a/libbuild2/lexer.cxx
+++ b/libbuild2/lexer.cxx
@@ -63,8 +63,8 @@ namespace build2
       }
     case lexer_mode::case_patterns:
       {
-        s1 = " $(){}[],|#\t\n";
-        s2 = "             ";
+        s1 = " $(){}[],|:#\t\n";
+        s2 = "              ";
         break;
       }
     case lexer_mode::attribute:
@@ -201,9 +201,10 @@ namespace build2
     // The following characters are special in the normal, variable, and
     // switch_expressions modes.
     //
-    if (m == lexer_mode::normal   ||
-        m == lexer_mode::variable ||
-        m == lexer_mode::switch_expressions)
+    if (m == lexer_mode::normal             ||
+        m == lexer_mode::variable           ||
+        m == lexer_mode::switch_expressions ||
+        m == lexer_mode::case_patterns)
     {
       switch (c)
       {
diff --git a/libbuild2/lexer.hxx b/libbuild2/lexer.hxx
index 72ec050..90d546d 100644
--- a/libbuild2/lexer.hxx
+++ b/libbuild2/lexer.hxx
@@ -33,7 +33,7 @@ namespace build2
   // a few extra characters:
   //
   //   switch_expressions  values plus `:`
-  //   case_patterns       values plus '|'
+  //   case_patterns       values plus '|' and ':'
   //
   // Note that the normal, value/values and derived, as well as eval modes
   // split words separated by the pair character (to disable pairs one can
diff --git a/libbuild2/parser.cxx b/libbuild2/parser.cxx
index d457c68..a8abbfb 100644
--- a/libbuild2/parser.cxx
+++ b/libbuild2/parser.cxx
@@ -2141,7 +2141,7 @@ namespace build2
     // multiple `case`s per line/block) optionally followed by the `default`
     // lines/blocks followed by the closing `}`.
     //
-    bool taken (false); // One of the cases/default has been taken.
+    bool taken (false); // One of the case/default has been taken.
     bool seen_default (false);
 
     auto special = [&seen_default, this] (const token& t, const type& tt)
@@ -2279,6 +2279,16 @@ namespace build2
               break;
             }
 
+            // We reserve the ':' separator for possible future match
+            // extraction support:
+            //
+            // case '...': x
+            //   info "$x"
+            //
+            if (tt == type::colon)
+              fail (t) << "unexpected ':' (match extraction is not yet "
+                       << "supported)";
+
             if (tt != type::comma)
               break;
           }
diff --git a/tests/switch/testscript b/tests/switch/testscript
index c8adaf0..f6c3753 100644
--- a/tests/switch/testscript
+++ b/tests/switch/testscript
@@ -312,3 +312,15 @@ switch 1: no_such_matcher
 EOI
 <stdin>:3:8: error: unmatched call to no_such_matcher(<untyped>, <untyped>)
 EOE
+
+: match-extraction
+:
+$* <<EOI 2>>EOE != 0
+switch 1
+{
+  case 1: y
+    x = $y
+}
+EOI
+<stdin>:3:9: error: unexpected ':' (match extraction is not yet supported)
+EOE
-- 
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