[C++ PATCH] New warning for extra semicolons after in-class function definitions

[Volker Reichelt <v dot reichelt at netcologne dot de>]

Hi,

with the following patch I suggest to add a diagnostic for extra
semicolons after in-class member function definitions:

  struct A
  {
    A() {};
    void foo() {};
    friend void bar() {};
  };

Although they are allowed in the C++ standard, people (including me)
often like to get rid of them for stylistic/consistency reasons.
In fact clang has a warning -Wextra-semi for this.

Also in GCC (almost exactly 10 years ago) there was a patch
https://gcc.gnu.org/ml/gcc-cvs/2007-03/msg00841.html
to issue a pedwarn (which had to be reverted as GCC would reject valid
code because of the pedwarn).

Instead of using pewarn the patch below adds a new warning (named like
clang's) to warn about these redundant semicolons.
Btw, clang's warning message "extra ';' after member function definition"
is slightly incorrect because it is also emitted for friend functions
which are not member-functions. That's why I suggest a different wording:

  Wextra-semi.C:3:9: warning: extra ';' after in-class function definition [-Wextra-semi]
     A() {};
           ^
  Wextra-semi.C:4:16: warning: extra ';' after in-class function definition [-Wextra-semi]
     void foo() {};
                  ^
  Wextra-semi.C:5:23: warning: extra ';' after in-class function definition [-Wextra-semi]
     friend void bar() {};
                         ^

Bootstrapped and regtested on x86_64-pc-linux-gnu.

OK for stage 1, once GCC 7 has branched?

Regards,
Volker


2017-04-07  Volker Reichelt  <v.reichelt@netcologne.de>

	* c.opt (Wextra-semi): New C++ warning flag.

Index: gcc/c-family/c.opt
===================================================================
--- gcc/c-family/c.opt	(revision 246752)
+++ gcc/c-family/c.opt	(working copy)
@@ -504,6 +504,10 @@
 C ObjC C++ ObjC++ Warning
 ; in common.opt
 
+Wextra-semi
+C++ Var(warn_extra_semi) Warning
+Warn about semicolon after in-class function definition.
+
 Wfloat-conversion
 C ObjC C++ ObjC++ Var(warn_float_conversion) Warning LangEnabledBy(C ObjC C++ ObjC++,Wconversion)
 Warn for implicit type conversions that cause loss of floating point precision.

2017-04-07  Volker Reichelt  <v.reichelt@netcologne.de>

	* parser.c (cp_parser_member_declaration): Add warning for
	extra semicolon after in-class function definition.

Index: gcc/cp/parser.c
===================================================================
--- gcc/cp/parser.c	(revision 246752)
+++ gcc/cp/parser.c	(working copy)
@@ -23386,7 +23386,11 @@
 		  token = cp_lexer_peek_token (parser->lexer);
 		  /* If the next token is a semicolon, consume it.  */
 		  if (token->type == CPP_SEMICOLON)
-		    cp_lexer_consume_token (parser->lexer);
+		    {
+		      cp_lexer_consume_token (parser->lexer);
+		      warning (OPT_Wextra_semi, "extra %<;%> "
+			       "after in-class function definition");
+		    }
 		  goto out;
 		}
 	      else

2017-04-07  Volker Reichelt  <v.reichelt@netcologne.de>

	* g++.dg/warn/Wextra-semi.C: New test.

Index: gcc/testsuite/g++.dg/warn/Wextra-semi.C
===================================================================
--- gcc/testsuite/g++.dg/warn/Wextra-semi.C	2017-04-07
+++ gcc/testsuite/g++.dg/warn/Wextra-semi.C	2017-04-07
@@ -0,0 +1,8 @@
+// { dg-options "-Wextra-semi" }
+
+struct A
+{
+  A() {};		// { dg-warning "after in-class function definition" }
+  void foo() {};	// { dg-warning "after in-class function definition" }
+  friend void bar() {};	// { dg-warning "after in-class function definition" }
+};
===================================================================