[PATCH v3] Improve bad error message with stray semicolon in initializer (and related) [PR101232]

[Franciszek Witt]

Hi, could someone review this patch?

This is built on top of the v2 from
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101232 the only
difference is fix for error59.C

I have tested it on x86_64 Ubuntu 22 machine.


Regards
Franciszek

---

Author: Franciszek Witt <franek.w...@gmail.com>
Date:   Mon Aug 5 09:00:35 2024 +0200

    c++: [PR101232]

            PR c++/101232

    gcc/cp/ChangeLog:

            * parser.cc (cp_parser_postfix_expression): Commit to the
parse in case we know its either a cast or invalid syntax.
            (cp_parser_braced_list): Add a heuristic to inform about
missing comma or operator.

    gcc/testsuite/ChangeLog:

            * g++.dg/parse/error59.C: Change the test so the new error
message is accepted.
            * g++.dg/cpp0x/initlist-err1.C: New test.
            * g++.dg/cpp0x/initlist-err2.C: New test.
            * g++.dg/cpp0x/initlist-err3.C: New test.

---

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index 1dd0efaf963..2e0ce1c6ddb 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -7881,8 +7881,13 @@ cp_parser_postfix_expression (cp_parser
*parser, bool address_p, bool cast_p,
         --parser->prevent_constrained_type_specifiers;
        /* Parse the cast itself.  */
        if (!cp_parser_error_occurred (parser))
-         postfix_expression
-           = cp_parser_functional_cast (parser, type);
+         {
+           if (cp_lexer_next_token_is (parser->lexer, CPP_OPEN_BRACE))
+             /* This can only be a cast.  */
+             cp_parser_commit_to_topmost_tentative_parse (parser);
+           postfix_expression
+             = cp_parser_functional_cast (parser, type);
+         }
        /* If that worked, we're done.  */
        if (cp_parser_parse_definitely (parser))
          break;
@@ -26350,8 +26355,19 @@ cp_parser_braced_list (cp_parser *parser,
bool *non_constant_p /*=nullptr*/)
   else if (non_constant_p)
     *non_constant_p = false;
   /* Now, there should be a trailing `}'.  */
-  location_t finish_loc = cp_lexer_peek_token (parser->lexer)->location;
-  braces.require_close (parser);
+  cp_token * token = cp_lexer_peek_token (parser->lexer);
+  location_t finish_loc = token->location;
+  if (!braces.require_close (parser))
+    {
+      /* This is just a heuristic. */
+      if (token->type != CPP_SEMICOLON)
+        {
+          inform (finish_loc,
+            "probably missing a comma or an operator before");
+          if (cp_parser_skip_to_closing_brace (parser))
+            cp_lexer_consume_token (parser->lexer);
+        }
+    }
   TREE_TYPE (initializer) = init_list_type_node;
   recompute_constructor_flags (initializer);

diff --git a/gcc/testsuite/g++.dg/cpp0x/initlist-err1.C
b/gcc/testsuite/g++.dg/cpp0x/initlist-err1.C
new file mode 100644
index 00000000000..6ea8afb3273
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/initlist-err1.C
@@ -0,0 +1,11 @@
+// PR c++/101232
+// { dg-do compile { target c++11 } }
+
+struct X {
+    int a;
+    int b;
+};
+
+void f() {
+    auto x = X{ 1, 2; };       // { dg-error "21:" }
+}                              // { dg-prune-output "expected declaration" }
diff --git a/gcc/testsuite/g++.dg/cpp0x/initlist-err2.C
b/gcc/testsuite/g++.dg/cpp0x/initlist-err2.C
new file mode 100644
index 00000000000..227f519dc19
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/initlist-err2.C
@@ -0,0 +1,11 @@
+// PR c++/101232
+// { dg-do compile { target c++11 } }
+
+struct X {
+    int a;
+    int b;
+};
+
+void f() {
+    auto x = X{ 1 2 }; // { dg-error "19:.*probably" }
+}
diff --git a/gcc/testsuite/g++.dg/cpp0x/initlist-err3.C
b/gcc/testsuite/g++.dg/cpp0x/initlist-err3.C
new file mode 100644
index 00000000000..b77ec9bf4e9
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/initlist-err3.C
@@ -0,0 +1,11 @@
+// PR c++/101232
+// { dg-do compile { target c++11 } }
+
+struct X {
+    int a;
+    int b;
+};
+
+void f() {
+    auto x = X{ 1, {2 };       // { dg-error "expected.*before" }
+}
diff --git a/gcc/testsuite/g++.dg/parse/error59.C
b/gcc/testsuite/g++.dg/parse/error59.C
index 2c44e210366..d782c9b1616 100644
--- a/gcc/testsuite/g++.dg/parse/error59.C
+++ b/gcc/testsuite/g++.dg/parse/error59.C
@@ -3,4 +3,4 @@
 void foo()
 {
   (struct {}x){}; // { dg-error "" }
-}
+}                 // { dg-excess-errors "" }