re PR preprocessor/36320 (Required diagnosis of syntax error missed)

gcc/testsuite
	PR preprocessor/36320:
	* gcc.dg/cpp/pr36320.c: New file.
libcpp
	PR preprocessor/36320:
	* internal.h (_cpp_parse_expr): Update.
	* expr.c (_cpp_parse_expr): Add 'is_if' argument.  Update error
	messages.
	* directives.c (do_if): Update.
	(do_elif): Require expression if processing group.

From-SVN: r136209

gcc/testsuite/ChangeLog

+2008-05-30  Tom Tromey  <tromey@redhat.com>
+
+	PR preprocessor/36320:
+	* gcc.dg/cpp/pr36320.c: New file.
+
 2008-05-29  Paolo Carlini  <paolo.carlini@oracle.com>
 
         PR c++/35243

gcc/testsuite/gcc.dg/cpp/pr36320.c

+/* PR 36320 - #elif still requires valid expression.  */
+
+/* { dg-do preprocess } */
+
+int z;
+#if 1
+#elif   /* { dg-error "with no expression" } */
+#endif

libcpp/ChangeLog

+2008-05-30  Tom Tromey  <tromey@redhat.com>
+
+	PR preprocessor/36320:
+	* internal.h (_cpp_parse_expr): Update.
+	* expr.c (_cpp_parse_expr): Add 'is_if' argument.  Update error
+	messages.
+	* directives.c (do_if): Update.
+	(do_elif): Require expression if processing group.
+
 2008-05-30  Danny Smith  <dannysmith@users.sourceforge.net>
 
 	* include/cpplib.h (struct cpp_dir): Add new field, canonical_name.

libcpp/directives.c

@@ -1737,7 +1737,7 @@ do_if (cpp_reader *pfile)
   int skip = 1;
 
   if (! pfile->state.skipping)
-    skip = _cpp_parse_expr (pfile) == false;
+    skip = _cpp_parse_expr (pfile, true) == false;
 
   push_conditional (pfile, skip, T_IF, pfile->mi_ind_cmacro);
 }
@@ -1796,15 +1796,23 @@ do_elif (cpp_reader *pfile)
 	}
       ifs->type = T_ELIF;
 
-      /* Only evaluate this if we aren't skipping elses.  During
-	 evaluation, set skipping to false to get lexer warnings.  */
-      if (ifs->skip_elses)
-	pfile->state.skipping = 1;
-      else
+      if (! ifs->was_skipping)
 	{
+	  bool value;
+	  /* The standard mandates that the expression be parsed even
+	     if we are skipping elses at this point -- the lexical
+	     restrictions on #elif only apply to skipped groups, but
+	     this group is not being skipped.  Temporarily set
+	     skipping to false to get lexer warnings.  */
 	  pfile->state.skipping = 0;
-	  pfile->state.skipping = ! _cpp_parse_expr (pfile);
-	  ifs->skip_elses = ! pfile->state.skipping;
+	  value = _cpp_parse_expr (pfile, false);
+	  if (ifs->skip_elses)
+	    pfile->state.skipping = 1;
+	  else
+	    {
+	      pfile->state.skipping = ! value;
+	      ifs->skip_elses = value;
+	    }
 	}
 
       /* Invalidate any controlling macro.  */

libcpp/expr.c

@@ -852,7 +852,7 @@ static const struct cpp_operator
    stored in the 'value' field of the stack element of the operator
    that precedes it.  */
 bool
-_cpp_parse_expr (cpp_reader *pfile)
+_cpp_parse_expr (cpp_reader *pfile, bool is_if)
 {
   struct op *top = pfile->op_stack;
   unsigned int lex_count;
@@ -927,7 +927,7 @@ _cpp_parse_expr (cpp_reader *pfile)
 	    SYNTAX_ERROR ("missing expression between '(' and ')'");
 
 	  if (op.op == CPP_EOF && top->op == CPP_EOF)
- 	    SYNTAX_ERROR ("#if with no expression");
+ 	    SYNTAX_ERROR2 ("%s with no expression", is_if ? "#if" : "#elif");
 
  	  if (top->op != CPP_EOF && top->op != CPP_OPEN_PAREN)
  	    SYNTAX_ERROR2 ("operator '%s' has no right operand",
@@ -988,7 +988,8 @@ _cpp_parse_expr (cpp_reader *pfile)
 
   if (top != pfile->op_stack)
     {
-      cpp_error (pfile, CPP_DL_ICE, "unbalanced stack in #if");
+      cpp_error (pfile, CPP_DL_ICE, "unbalanced stack in %s",
+		 is_if ? "#if" : "#elif");
     syntax_error:
       return false;  /* Return false on syntax error.  */
     }

libcpp/internal.h

@@ -557,7 +557,7 @@ extern bool _cpp_read_file_entries (cpp_reader *, FILE *);
 extern struct stat *_cpp_get_file_stat (_cpp_file *);
 
 /* In expr.c */
-extern bool _cpp_parse_expr (cpp_reader *);
+extern bool _cpp_parse_expr (cpp_reader *, bool);
 extern struct op *_cpp_expand_op_stack (cpp_reader *);
 
 /* In lex.c */