c: Turn -Wimplicit-int into a permerror

Most of these new permerrors are currently not diagnosed in system
headers.

gcc/

	PR c/91093
	PR c/96284
	* doc/invoke.texi (Warning Options): Document changes.

gcc/c/

	* c-decl.cc (warn_defaults_to): Remove.
	(grok_declarator, start_function): Call permerror_opt
	instead of warn_defaults_to.
	(store_parm_decls_oldstyle): Call permerror_opt for
	OPT_Wimplicit_int.

gcc/testsuite/

	* gcc.dg/permerror-default.c (implicit_int_1, implicit_int_2)
	(implicit_int_3, implicit_int_4): Expect new permerror.
	* gcc.dg/permerror-system.c: Expect a single new permerror.
	* gcc.dg/Wimplicit-int-1.c: Compile with -fpermissive due to
	expected warning.
	* gcc.dg/Wimplicit-int-4.c: Likewise.
	* gcc.dg/Wimplicit-int-1a.c: New test.  Copied from
	gcc.dg/Wimplicit-int-1.c, but expect errors.
	* gcc.dg/Wimplicit-int-4a.c: New test.  Copied from
	gcc.dg/Wimplicit-int-4.c, but expect errors.
	* gcc.dg/gnu23-attr-syntax-2.c: Compile with -fpermissive
	due to expected implicit-int error.
	* gcc.dg/gnu23-attr-syntax-3.c: New test.  Copied from
	gcc.dg/gnu23-attr-syntax-2.c, but expect an error.
	* gcc.dg/pr105635.c: Build with -fpermissive due to implicit
	int.
	* gcc.dg/pr105635-2.c: New test.  Copied from
	gcc.dg/pr105635.c.  Expect implicit int error.
	* gcc.dg/noncompile/pr79758.c: Build with -fpermissive due to
	implicit int.
	* gcc.dg/noncompile/pr79758-2.c: New test.  Copied from
	gcc.dg/noncompile/pr79758.c.  Expect implicit int error.

14 files changed, 86 insertions, 43 deletions

diff --git a/gcc/c/c-decl.cc b/gcc/c/c-decl.cc
index 4d17f05..14d66ff 100644
--- a/gcc/c/c-decl.cc
+++ b/gcc/c/c-decl.cc
@@ -647,8 +647,6 @@ static tree grokdeclarator (const struct c_declarator *,
 			    bool *, enum deprecated_states);
 static tree grokparms (struct c_arg_info *, bool);
 static void layout_array_type (tree);
-static void warn_defaults_to (location_t, int, const char *, ...)
-    ATTRIBUTE_GCC_DIAG(3,4);
 static const char *header_for_builtin_fn (tree);
 
 /* T is a statement.  Add it to the statement-tree.  This is the
@@ -6576,23 +6574,6 @@ warn_variable_length_array (tree name, tree size)
     }
 }
 
-/* Print warning about defaulting to int if necessary.  */
-
-static void
-warn_defaults_to (location_t location, int opt, const char *gmsgid, ...)
-{
-  diagnostic_info diagnostic;
-  va_list ap;
-  rich_location richloc (line_table, location);
-
-  va_start (ap, gmsgid);
-  diagnostic_set_info (&diagnostic, gmsgid, &ap, &richloc,
-                       flag_isoc99 ? DK_PEDWARN : DK_WARNING);
-  diagnostic.option_index = opt;
-  diagnostic_report_diagnostic (global_dc, &diagnostic);
-  va_end (ap);
-}
-
 /* Returns the smallest location != UNKNOWN_LOCATION in LOCATIONS,
    considering only those c_declspec_words found in LIST, which
    must be terminated by cdw_number_of_elements.  */
@@ -6881,12 +6862,12 @@ grokdeclarator (const struct c_declarator *declarator,
       else
 	{
 	  if (name)
-	    warn_defaults_to (loc, OPT_Wimplicit_int,
-			      "type defaults to %<int%> in declaration "
-			      "of %qE", name);
+	    permerror_opt (loc, OPT_Wimplicit_int,
+			   "type defaults to %<int%> in declaration "
+			   "of %qE", name);
 	  else
-	    warn_defaults_to (loc, OPT_Wimplicit_int,
-			      "type defaults to %<int%> in type name");
+	    permerror_opt (loc, OPT_Wimplicit_int,
+			   "type defaults to %<int%> in type name");
 	}
     }
 
@@ -10300,10 +10281,10 @@ start_function (struct c_declspecs *declspecs, struct c_declarator *declarator,
     }
 
   if (warn_about_return_type)
-    warn_defaults_to (loc, flag_isoc99 ? OPT_Wimplicit_int
-			   : (warn_return_type > 0 ? OPT_Wreturn_type
-			      : OPT_Wimplicit_int),
-		      "return type defaults to %<int%>");
+    permerror_opt (loc, flag_isoc99 ? OPT_Wimplicit_int
+		   : (warn_return_type > 0 ? OPT_Wreturn_type
+		      : OPT_Wimplicit_int),
+		   "return type defaults to %<int%>");
 
   /* Make the init_value nonzero so pushdecl knows this is not tentative.
      error_mark_node is replaced below (in pop_scope) with the BLOCK.  */
@@ -10645,9 +10626,9 @@ store_parm_decls_oldstyle (tree fndecl, const struct c_arg_info *arg_info)
 	  warn_if_shadowing (decl);
 
 	  if (flag_isoc99)
-	    pedwarn (DECL_SOURCE_LOCATION (decl),
-		     OPT_Wimplicit_int, "type of %qD defaults to %<int%>",
-		     decl);
+	    permerror_opt (DECL_SOURCE_LOCATION (decl),
+			   OPT_Wimplicit_int, "type of %qD defaults to %<int%>",
+			   decl);
 	  else
 	    warning_at (DECL_SOURCE_LOCATION (decl),
 			OPT_Wmissing_parameter_type,
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 5244958..51bf19d 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -6185,6 +6185,7 @@ that have their own flag:
 
 @gccoptlist{
 -Wimplicit-function-declaration @r{(C and Objective-C only)}
+-Wimplicit-int @r{(C and Objective-C only)}
 -Wint-conversion @r{(C and Objective-C only)}
 -Wnarrowing @r{(C++)}
 }
@@ -6856,8 +6857,10 @@ This warning is enabled by @option{-Wall} in C++.
 @opindex Wno-implicit-int
 @item -Wno-implicit-int @r{(C and Objective-C only)}
 This option controls warnings when a declaration does not specify a type.
-This warning is enabled by default in C99 and later dialects of C,
-and also by @option{-Wall}.
+This warning is enabled by default, as an error, in C99 and later
+dialects of C, and also by @option{-Wall}.  The error can be downgraded
+to a warning using @option{-fpermissive} (along with certain other
+errors), or for this error alone, with @option{-Wno-error=implicit-int}.
 
 This warning is upgraded to an error by @option{-pedantic-errors}.
 
diff --git a/gcc/testsuite/gcc.dg/Wimplicit-int-1.c b/gcc/testsuite/gcc.dg/Wimplicit-int-1.c
index 4a96e8f..fc7726c 100644
--- a/gcc/testsuite/gcc.dg/Wimplicit-int-1.c
+++ b/gcc/testsuite/gcc.dg/Wimplicit-int-1.c
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "" } */
+/* { dg-options "-fpermissive" } */
 
 static l; /* { dg-warning "type defaults to" } */
 
diff --git a/gcc/testsuite/gcc.dg/Wimplicit-int-1a.c b/gcc/testsuite/gcc.dg/Wimplicit-int-1a.c
new file mode 100644
index 0000000..ef1835e
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/Wimplicit-int-1a.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "" } */
+
+static l; /* { dg-error "type defaults to" } */
+
+foo (a) /* { dg-error "return type defaults to" } */
+/* { dg-error "type of .a. defaults to .int." "type" { target *-*-* } .-1 } */
+{
+  auto p; /* { dg-error "type defaults to" } */
+  typedef bar; /* { dg-error "type defaults to" } */
+}
diff --git a/gcc/testsuite/gcc.dg/Wimplicit-int-4.c b/gcc/testsuite/gcc.dg/Wimplicit-int-4.c
index c9c6e8e..99c61a7 100644
--- a/gcc/testsuite/gcc.dg/Wimplicit-int-4.c
+++ b/gcc/testsuite/gcc.dg/Wimplicit-int-4.c
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-Wno-implicit -Wimplicit-int" } */
+/* { dg-options "-fpermissive -Wno-implicit -Wimplicit-int" } */
 
 static l; /* { dg-warning "type defaults to" } */
 
diff --git a/gcc/testsuite/gcc.dg/Wimplicit-int-4a.c b/gcc/testsuite/gcc.dg/Wimplicit-int-4a.c
new file mode 100644
index 0000000..920a088
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/Wimplicit-int-4a.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-Wno-implicit -Wimplicit-int" } */
+
+static l; /* { dg-error "type defaults to" } */
+
+foo (a) /* { dg-error "return type defaults to" } */
+/* { dg-error "type of .a. defaults to .int." "type" { target *-*-* } .-1 } */
+{
+  auto p; /* { dg-error "type defaults to" } */
+  typedef bar; /* { dg-error "type defaults to" } */
+}
diff --git a/gcc/testsuite/gcc.dg/gnu23-attr-syntax-2.c b/gcc/testsuite/gcc.dg/gnu23-attr-syntax-2.c
index ba60f7a..8943534 100644
--- a/gcc/testsuite/gcc.dg/gnu23-attr-syntax-2.c
+++ b/gcc/testsuite/gcc.dg/gnu23-attr-syntax-2.c
@@ -1,7 +1,7 @@
 /* Test C23 attribute syntax.  Invalid uses of attributes with GNU C
    features.  */
 /* { dg-do compile } */
-/* { dg-options "-std=gnu23 -w" } */
+/* { dg-options "-fpermissive -std=gnu23 -w" } */
 
 /* Attributes cannot be used as prefix attributes on old-style
    parameter declarations or on function declarators with identifier
diff --git a/gcc/testsuite/gcc.dg/gnu23-attr-syntax-3.c b/gcc/testsuite/gcc.dg/gnu23-attr-syntax-3.c
new file mode 100644
index 0000000..d73d6a3
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/gnu23-attr-syntax-3.c
@@ -0,0 +1,17 @@
+/* Test C23 attribute syntax.  Invalid uses of attributes with GNU C
+   features.  Non-permissive variant.  */
+/* { dg-do compile } */
+/* { dg-options "-std=gnu23 -w" } */
+
+/* Attributes cannot be used as prefix attributes on old-style
+   parameter declarations or on function declarators with identifier
+   lists (removed from C23).  */
+
+void (*f(a, b) [[]])() int a, b; { } /* { dg-error "expected" } */
+
+void f(x, y) int x; [[]] int y; { } /* { dg-error "expected" } */
+/* { dg-error "type of 'y' defaults to 'int'" "" { target *-*-* } .-1 } */
+
+/* Nonempty attributes cannot be used as postfix attributes with
+   __auto_type.  */
+__auto_type [[gnu::no_such_attr]] x = 1; /* { dg-error "'__auto_type' followed by" } */
diff --git a/gcc/testsuite/gcc.dg/noncompile/pr79758-2.c b/gcc/testsuite/gcc.dg/noncompile/pr79758-2.c
new file mode 100644
index 0000000..e6a27f9
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/noncompile/pr79758-2.c
@@ -0,0 +1,6 @@
+/* PR c/79758 */
+/* { dg-do compile } */
+
+void fn1 (int[a]) { }; /* { dg-error "undeclared here" } */
+void fn1 (b) { }; /* { dg-error "redefinition" } */
+/* { dg-error "defaults to 'int'" "" { target *-*-* } .-1 } */
diff --git a/gcc/testsuite/gcc.dg/noncompile/pr79758.c b/gcc/testsuite/gcc.dg/noncompile/pr79758.c
index a312160..e42a443 100644
--- a/gcc/testsuite/gcc.dg/noncompile/pr79758.c
+++ b/gcc/testsuite/gcc.dg/noncompile/pr79758.c
@@ -1,5 +1,6 @@
 /* PR c/79758 */
 /* { dg-do compile } */
+/* { dg-additional-options "-fpermissive" } */
 
 void fn1 (int[a]) { }; /* { dg-error "undeclared here" } */
 void fn1 (b) { }; /* { dg-error "redefinition" } */
diff --git a/gcc/testsuite/gcc.dg/permerror-default.c b/gcc/testsuite/gcc.dg/permerror-default.c
index f37f918..90f2220 100644
--- a/gcc/testsuite/gcc.dg/permerror-default.c
+++ b/gcc/testsuite/gcc.dg/permerror-default.c
@@ -10,13 +10,13 @@ implicit_function_declaration (void)
   f1 (); /* { dg-error "'f1' \\\[-Wimplicit-function-declaration\\\]" } */
 }
 
-extern implicit_int_1; /* { dg-warning "'implicit_int_1' \\\[-Wimplicit-int\\\]" } */
-typedef implicit_int_2; /* { dg-warning "'implicit_int_2' \\\[-Wimplicit-int\\\]" } */
-extern implicit_int_3 (void); /* { dg-warning "'implicit_int_3' \\\[-Wimplicit-int\\]" } */
-implicit_int_4 (i) /* { dg-warning "return type defaults to 'int' \\\[-Wimplicit-int\\\]" } */
-/* { dg-warning "type of 'i' defaults to 'int' \\\[-Wimplicit-int\\\]" "" { target *-*-*} .-1 } */
+extern implicit_int_1; /* { dg-error "'implicit_int_1' \\\[-Wimplicit-int\\\]" } */
+typedef implicit_int_2; /* { dg-error "'implicit_int_2' \\\[-Wimplicit-int\\\]" } */
+extern implicit_int_3 (void); /* { dg-error "'implicit_int_3' \\\[-Wimplicit-int\\]" } */
+implicit_int_4 (i) /* { dg-error "return type defaults to 'int' \\\[-Wimplicit-int\\\]" } */
+/* { dg-error "type of 'i' defaults to 'int' \\\[-Wimplicit-int\\\]" "" { target *-*-*} .-1 } */
 {
-  (const) 0; /* { dg-warning "type defaults to 'int' in type name \\\[-Wimplicit-int\\\]" } */
+  (const) 0; /* { dg-error "type defaults to 'int' in type name \\\[-Wimplicit-int\\\]" } */
 }
 
 extern int missing_parameter_type (i); /* { dg-warning "parameter names \\\(without types\\\) in function declaration\n" } */
diff --git a/gcc/testsuite/gcc.dg/permerror-system.c b/gcc/testsuite/gcc.dg/permerror-system.c
index e4da4a9..60c65ff 100644
--- a/gcc/testsuite/gcc.dg/permerror-system.c
+++ b/gcc/testsuite/gcc.dg/permerror-system.c
@@ -10,6 +10,8 @@
 
 /* { dg-error "'f1' \\\[-Wimplicit-function-declaration\\\]" "" { target *-*-* } 10 } */
 
+/* { dg-error "type of 'i' defaults to 'int' \\\[-Wimplicit-int\\\]" "" { target *-*-*} 16 } */
+
 /* { dg-error "pointer/integer type mismatch in conditional expression \\\[-Wint-conversion\\\]" "" { target *-*-* } 29 } */
 /* { dg-error "pointer/integer type mismatch in conditional expression \\\[-Wint-conversion\\\]" "" { target *-*-* } 30 } */
 /* { dg-error "passing argument 1 of 'f2' makes pointer from integer without a cast \\\[-Wint-conversion\\\]" "" { target *-*-* } 31 } */
diff --git a/gcc/testsuite/gcc.dg/pr105635-2.c b/gcc/testsuite/gcc.dg/pr105635-2.c
new file mode 100644
index 0000000..807eef0
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr105635-2.c
@@ -0,0 +1,11 @@
+/* PR c/105635 */
+/* { dg-do compile } */
+/* { dg-options "-Wall" } */
+
+void foo (int, int[*]);	/* { dg-message "previous declaration of 'foo' with type" } */
+
+foo (int x, int y)	/* { dg-error "return type defaults to 'int'" } */
+{			/* { dg-warning "conflicting types for 'foo'" "" { target *-*-* } .-1 } */
+			/* { dg-message "declared here" "" { target *-*-* } .-2 } */
+  return (x >= 0) != (y < 0);	/* { dg-warning "'return' with a value, in function returning void" } */
+}
diff --git a/gcc/testsuite/gcc.dg/pr105635.c b/gcc/testsuite/gcc.dg/pr105635.c
index aa02f59..b98ea1b 100644
--- a/gcc/testsuite/gcc.dg/pr105635.c
+++ b/gcc/testsuite/gcc.dg/pr105635.c
@@ -1,6 +1,6 @@
 /* PR c/105635 */
 /* { dg-do compile } */
-/* { dg-options "-Wall" } */
+/* { dg-options "-fpermissive -Wall" } */
 
 void foo (int, int[*]);	/* { dg-message "previous declaration of 'foo' with type" } */