r178105 - [modules] Re-enable the "ambiguous expansion of macro" warning.
Argyrios Kyrtzidis
akyrtzi at gmail.com
Fri Oct 25 16:25:57 PDT 2013
On Oct 25, 2013, at 2:44 PM, Richard Smith <richard at metafoo.co.uk> wrote:
> On Tue, Mar 26, 2013 at 6:25 PM, Argyrios Kyrtzidis <akyrtzi at gmail.com> wrote:
> Author: akirtzidis
> Date: Tue Mar 26 20:25:19 2013
> New Revision: 178105
>
> URL: http://llvm.org/viewvc/llvm-project?rev=178105&view=rev
> Log:
> [modules] Re-enable the "ambiguous expansion of macro" warning.
>
> Also update "test/Modules/macros.c" to test modified semantics:
> -When there is an ambiguous macro, expand using the latest introduced version, not the first one.
> -#undefs in submodules cause the macro to not be exported by that submodule, it doesn't cause
> undefining of macros in the translation unit that imported that submodule.
> This reduces macro namespace interference across modules.
>
> Modified:
> cfe/trunk/lib/Lex/PPMacroExpansion.cpp
> cfe/trunk/test/Modules/macros.c
>
> Modified: cfe/trunk/lib/Lex/PPMacroExpansion.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Lex/PPMacroExpansion.cpp?rev=178105&r1=178104&r2=178105&view=diff
> ==============================================================================
> --- cfe/trunk/lib/Lex/PPMacroExpansion.cpp (original)
> +++ cfe/trunk/lib/Lex/PPMacroExpansion.cpp Tue Mar 26 20:25:19 2013
> @@ -211,7 +211,9 @@ bool Preprocessor::isNextPPTokenLParen()
> /// expanded as a macro, handle it and return the next token as 'Identifier'.
> bool Preprocessor::HandleMacroExpandedIdentifier(Token &Identifier,
> MacroDirective *MD) {
> - MacroInfo *MI = MD->getMacroInfo();
> + MacroDirective::DefInfo Def = MD->getDefinition();
> + assert(Def.isValid());
> + MacroInfo *MI = Def.getMacroInfo();
>
> // If this is a macro expansion in the "#if !defined(x)" line for the file,
> // then the macro could expand to different things in other contexts, we need
> @@ -286,25 +288,22 @@ bool Preprocessor::HandleMacroExpandedId
> }
> }
>
> - // FIXME: Temporarily disable this warning that is currently bogus with a PCH
> - // that redefined a macro without undef'ing it first (test/PCH/macro-redef.c).
> -#if 0
> // If the macro definition is ambiguous, complain.
> - if (MI->isAmbiguous()) {
> + if (Def.getDirective()->isAmbiguous()) {
> Diag(Identifier, diag::warn_pp_ambiguous_macro)
> << Identifier.getIdentifierInfo();
> Diag(MI->getDefinitionLoc(), diag::note_pp_ambiguous_macro_chosen)
> << Identifier.getIdentifierInfo();
> - for (MacroInfo *PrevMI = MI->getPreviousDefinition();
> - PrevMI && PrevMI->isDefined();
> - PrevMI = PrevMI->getPreviousDefinition()) {
> - if (PrevMI->isAmbiguous()) {
> - Diag(PrevMI->getDefinitionLoc(), diag::note_pp_ambiguous_macro_other)
> + for (MacroDirective::DefInfo PrevDef = Def.getPreviousDefinition();
> + PrevDef && !PrevDef.isUndefined();
> + PrevDef = PrevDef.getPreviousDefinition()) {
> + if (PrevDef.getDirective()->isAmbiguous()) {
> + Diag(PrevDef.getMacroInfo()->getDefinitionLoc(),
> + diag::note_pp_ambiguous_macro_other)
> << Identifier.getIdentifierInfo();
> }
> }
> }
> -#endif
>
> // If we started lexing a macro, enter the macro expansion body.
>
>
> Modified: cfe/trunk/test/Modules/macros.c
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Modules/macros.c?rev=178105&r1=178104&r2=178105&view=diff
> ==============================================================================
> --- cfe/trunk/test/Modules/macros.c (original)
> +++ cfe/trunk/test/Modules/macros.c Tue Mar 26 20:25:19 2013
> @@ -1,4 +1,3 @@
> -// XFAIL: *
> // RUN: rm -rf %t
> // RUN: %clang_cc1 -fmodules -x objective-c -emit-module -fmodules-cache-path=%t -fmodule-name=macros_top %S/Inputs/module.map
> // RUN: %clang_cc1 -fmodules -x objective-c -emit-module -fmodules-cache-path=%t -fmodule-name=macros_left %S/Inputs/module.map
> @@ -10,12 +9,12 @@
> // These notes come from headers in modules, and are bogus.
>
> // FIXME: expected-note{{previous definition is here}}
> +// FIXME: expected-note{{previous definition is here}} expected-note{{expanding this definition of 'LEFT_RIGHT_DIFFERENT'}}
> +// expected-note{{other definition of 'TOP_RIGHT_REDEF'}} expected-note{{expanding this definition of 'LEFT_RIGHT_DIFFERENT2'}}
> // expected-note{{other definition of 'LEFT_RIGHT_DIFFERENT'}}
> -// expected-note{{expanding this definition of 'TOP_RIGHT_REDEF'}}
> -// FIXME: expected-note{{previous definition is here}} \
> -// expected-note{{expanding this definition of 'LEFT_RIGHT_DIFFERENT'}}
>
> -// expected-note{{other definition of 'TOP_RIGHT_REDEF'}}
> +
> +// expected-note{{expanding this definition of 'TOP_RIGHT_REDEF'}}
>
> @import macros;
>
> @@ -80,8 +79,8 @@ void f() {
> # error TOP should be visible
> #endif
>
> -#ifdef TOP_LEFT_UNDEF
> -# error TOP_LEFT_UNDEF should not be visible
> +#ifndef TOP_LEFT_UNDEF
> +# error TOP_LEFT_UNDEF should still be defined
>
> This seems completely broken to me, and it breaks libc++.
>
> glibc has something like:
>
> // stdio.h
> int getc(FILE*);
> #define foo_getc(x) /* ... */
> #define getc(x) foo_getc(x)
>
> libc++ has:
>
> // cstdio
> #include <stdio.h>
>
> #ifdef getc
> #undef getc
> #endif
>
> namespace std { using ::getc; }
>
> This results in any program which includes <cstdio> being unable to use std::getc:
>
> // main.cc
> #include <cstdio>
> int k = std::getc(stdin); // error, no foo_getc in namespace std
>
> Can you explain a bit about the effect you were trying to achieve here? Here's another case:
>
> #include <stdio.h>
> #include <something>
> int k = getc(stdin); // still uses the macro from <stdio.h>
>
> I think we might want to ignore an #undef in <something> if <something> comes from a module that doesn't depend on the module containing <stdio.h>. (If it's just using the macro for its own internal purposes, or more generally if rearranging the order in which we chose to load the modules would result in a consistent macro definition chain.)
>
> I think the behavior we want here is:
>
> * If a module M1 depends on a module M2, macro definitions/undefs in M1 and M2 are never ambiguous (M1 is always ordered after M2).
> * If there are multiple ambiguous 'most recent' definitions of a macro (excluding chains that end in an undef), and the macro is used, warn.
>
> Put another way: consider the subgraph of the imported portion of the module dependency graph in which the macro is or was defined. All roots of that subgraph for which the macro is defined must define it to the same value, or we warn on ambiguity. If there are any such roots, the value of the macro is the value at such a root. Otherwise, the macro is not defined.
>
> Does that sound right to you?
I agree that for
@import cstdio
'cstdio' should be able to "not export" the 'getc' macro.
Without some language support to explicitly state whether you are undef'ing to avoid exporting vs undef'ing for internal use, I think it's reasonable to choose the former as default (undef'ing to avoid exporting).
I'm not so sure about M1 just disabling macros from M2, even when I have explicitly imported M2. I don't like that a module may affect another module import in a surprising way; for example:
(somewhere in a stack of headers getting included..)
@import M1 // this undefs macro BAZOO from module M2.
(...more headers).
// main.cc
@import M2 // imported so I can use BAZOO from module M2
BAZOO(0); // undefined ??
I imported M2 to use the macro that it exports, I should not need to know that M1 depends on M2 and it decided to undef macros from it.
If BAZOO macro is interfering with the usage of a symbol BAZOO from M1, then M1 should re-export M2 sans BAZOO, so I can use them both by just importing M1(like cstdio).
I mean:
1)
@import M1 // this re-exports M2 and re-purposes BAZOO; I can use symbols from both as M1 intended
2)
@import M1
@import M2 // I imported M2 and expect to be able to use the macros it exports, including BAZOO
3)
@import M2
@import M1
// same as 2)
4)
@import M1
@import M2
#undef BAZOO // I don't like that M2 exports BAZOO macro, I can choose to undef it.
Otherwise, with the suggested model of M1 disabling macros from M2:
5)
@import M1
@import M2
// There is no way to use symbols from both M1 and M2, and still get access to the BAZOO that M2 "advertises" that it is exporting.
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