george.burgess.iv created this revision. george.burgess.iv added reviewers: rsmith, aaron.ballman.
The following code is invalid before C99, since we try to declare `i` inside the first clause of the for loop: void foo() { for (int i = 0; i < 10; i++); } GCC does not accept this code in c89 or gnu89, but clang does: https://godbolt.org/g/ZWr3nA . If the user cares about GCC compatibility, we should probably warn about this if we're not in C99. I'm not 100% thrilled that we're emitting two warnings about the same thing for slightly different reasons; alternatives welcome. :) Repository: rC Clang https://reviews.llvm.org/D47840 Files: include/clang/Basic/DiagnosticParseKinds.td lib/Parse/ParseStmt.cpp test/Parser/gcc-for-loop-init-compatibility.c Index: test/Parser/gcc-for-loop-init-compatibility.c =================================================================== --- /dev/null +++ test/Parser/gcc-for-loop-init-compatibility.c @@ -0,0 +1,15 @@ +// RUN: %clang_cc1 -std=c89 -fsyntax-only -verify %s +// RUN: %clang_cc1 -std=gnu89 -fsyntax-only -verify %s +// RUN: %clang_cc1 -std=c99 -fsyntax-only -verify %s -DC99 + +#ifdef C99 +// expected-no-diagnostics +#endif + +void foo() { +#ifndef C99 + // expected-warning@+2{{GCC does not allow variable declarations in for loop initializers before C99}} +#endif + for (int i = 0; i < 10; i++) + ; +} Index: lib/Parse/ParseStmt.cpp =================================================================== --- lib/Parse/ParseStmt.cpp +++ lib/Parse/ParseStmt.cpp @@ -1622,8 +1622,10 @@ ForRange = true; } else if (isForInitDeclaration()) { // for (int X = 4; // Parse declaration, which eats the ';'. - if (!C99orCXXorObjC) // Use of C99-style for loops in C90 mode? + if (!C99orCXXorObjC) { // Use of C99-style for loops in C90 mode? Diag(Tok, diag::ext_c99_variable_decl_in_for_loop); + Diag(Tok, diag::warn_gcc_variable_decl_in_for_loop); + } // In C++0x, "for (T NS:a" might not be a typo for :: bool MightBeForRangeStmt = getLangOpts().CPlusPlus; Index: include/clang/Basic/DiagnosticParseKinds.td =================================================================== --- include/clang/Basic/DiagnosticParseKinds.td +++ include/clang/Basic/DiagnosticParseKinds.td @@ -173,6 +173,9 @@ def warn_gcc_attribute_location : Warning< "GCC does not allow an attribute in this position on a function declaration">, InGroup<GccCompat>; +def warn_gcc_variable_decl_in_for_loop : Warning< + "GCC does not allow variable declarations in for loop initializers before " + "C99">, InGroup<GccCompat>; def warn_attribute_no_decl : Warning< "attribute %0 ignored, because it is not attached to a declaration">, InGroup<IgnoredAttributes>;
Index: test/Parser/gcc-for-loop-init-compatibility.c =================================================================== --- /dev/null +++ test/Parser/gcc-for-loop-init-compatibility.c @@ -0,0 +1,15 @@ +// RUN: %clang_cc1 -std=c89 -fsyntax-only -verify %s +// RUN: %clang_cc1 -std=gnu89 -fsyntax-only -verify %s +// RUN: %clang_cc1 -std=c99 -fsyntax-only -verify %s -DC99 + +#ifdef C99 +// expected-no-diagnostics +#endif + +void foo() { +#ifndef C99 + // expected-warning@+2{{GCC does not allow variable declarations in for loop initializers before C99}} +#endif + for (int i = 0; i < 10; i++) + ; +} Index: lib/Parse/ParseStmt.cpp =================================================================== --- lib/Parse/ParseStmt.cpp +++ lib/Parse/ParseStmt.cpp @@ -1622,8 +1622,10 @@ ForRange = true; } else if (isForInitDeclaration()) { // for (int X = 4; // Parse declaration, which eats the ';'. - if (!C99orCXXorObjC) // Use of C99-style for loops in C90 mode? + if (!C99orCXXorObjC) { // Use of C99-style for loops in C90 mode? Diag(Tok, diag::ext_c99_variable_decl_in_for_loop); + Diag(Tok, diag::warn_gcc_variable_decl_in_for_loop); + } // In C++0x, "for (T NS:a" might not be a typo for :: bool MightBeForRangeStmt = getLangOpts().CPlusPlus; Index: include/clang/Basic/DiagnosticParseKinds.td =================================================================== --- include/clang/Basic/DiagnosticParseKinds.td +++ include/clang/Basic/DiagnosticParseKinds.td @@ -173,6 +173,9 @@ def warn_gcc_attribute_location : Warning< "GCC does not allow an attribute in this position on a function declaration">, InGroup<GccCompat>; +def warn_gcc_variable_decl_in_for_loop : Warning< + "GCC does not allow variable declarations in for loop initializers before " + "C99">, InGroup<GccCompat>; def warn_attribute_no_decl : Warning< "attribute %0 ignored, because it is not attached to a declaration">, InGroup<IgnoredAttributes>;
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