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C89 had a questionable feature where the compiler would implicitly declare a function that the user called but was never previously declared. The resulting function would be globally declared as extern int func(); -- a function without a prototype which accepts zero or more arguments. C99 removed support for this questionable feature due to severe security concerns. However, there was no deprecation period; C89 had the feature, C99 didn't. So Clang (and GCC) both supported the functionality as an extension in C99 and later modes. C2x no longer supports that function signature as it now requires all functions to have a prototype, and given the known security issues with the feature, continuing to support it as an extension is not tenable. This patch changes the diagnostic behavior for the -Wimplicit-function-declaration warning group depending on the language mode in effect. We continue to warn by default in C89 mode (due to the feature being dangerous to use). However, because this feature will not be supported in C2x mode, we've diagnosed it as being invalid for so long, the security concerns with the feature, and the trivial workaround for users (declare the function), we now default the extension warning to an error in C99-C17 mode. This still gives users an easy workaround if they are extensively using the extension in those modes (they can disable the warning or use -Wno-error to downgrade the error), but the new diagnostic makes it more clear that this feature is not supported and should be avoided. In C2x mode, we no longer allow an implicit function to be defined and treat the situation the same as any other lookup failure. Differential Revision: https://reviews.llvm.org/D122983
56 lines
3.3 KiB
C
56 lines
3.3 KiB
C
// RUN: %clang_cc1 %s -verify -fsyntax-only -Werror=implicit-function-declaration -std=c99
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// RUN: %clang_cc1 %s -verify -fsyntax-only -std=c11
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// RUN: %clang_cc1 %s -verify=c2x -fsyntax-only -std=c2x
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/// -Werror-implicit-function-declaration is a deprecated alias used by many projects.
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// RUN: %clang_cc1 %s -verify -fsyntax-only -Werror-implicit-function-declaration
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// c2x-note@*:* {{'__builtin_va_list' declared here}}
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typedef int int32_t;
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typedef unsigned char Boolean;
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extern int printf(__const char *__restrict __format, ...); // expected-note{{'printf' declared here}} \
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c2x-note {{'printf' declared here}}
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void func(void) {
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int32_t *vector[16];
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const char compDesc[16 + 1];
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int32_t compCount = 0;
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if (_CFCalendarDecomposeAbsoluteTimeV(compDesc, vector, compCount)) { // expected-error {{call to undeclared function '_CFCalendarDecomposeAbsoluteTimeV'; ISO C99 and later do not support implicit function declarations}} \
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expected-note {{previous implicit declaration}} \
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c2x-error {{use of undeclared identifier '_CFCalendarDecomposeAbsoluteTimeV'}}
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}
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printg("Hello, World!\n"); // expected-error{{call to undeclared function 'printg'; ISO C99 and later do not support implicit function declarations}} \
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expected-note{{did you mean 'printf'?}} \
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c2x-error {{use of undeclared identifier 'printg'; did you mean 'printf'?}}
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__builtin_is_les(1, 3); // expected-error{{use of unknown builtin '__builtin_is_les'}} \
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c2x-error {{unknown type name '__builtin_is_les'; did you mean '__builtin_va_list'?}} \
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c2x-error {{expected identifier or '('}} \
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c2x-error {{expected ')'}} \
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c2x-note {{to match this '('}}
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}
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Boolean _CFCalendarDecomposeAbsoluteTimeV(const char *componentDesc, int32_t **vector, int32_t count) { // expected-error {{conflicting types}}
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return 0;
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}
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// Test the typo-correction callback in Sema::ImplicitlyDefineFunction
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extern int sformatf(char *str, __const char *__restrict __format, ...); // expected-note{{'sformatf' declared here}}
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void test_implicit(void) {
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int formats = 0; // c2x-note {{'formats' declared here}}
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formatd("Hello, World!\n"); // expected-error{{call to undeclared function 'formatd'; ISO C99 and later do not support implicit function declarations}} \
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expected-note{{did you mean 'sformatf'?}} \
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c2x-error {{use of undeclared identifier 'formatd'; did you mean 'formats'?}} \
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c2x-error {{called object type 'int' is not a function or function pointer}}
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}
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void test_suggestion(void) {
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bark(); // expected-error {{call to undeclared function 'bark'; ISO C99 and later do not support implicit function declarations}} \
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c2x-error {{use of undeclared identifier 'bark'}}
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bork(); // expected-error {{call to undeclared function 'bork'; ISO C99 and later do not support implicit function declarations}} \
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c2x-error {{use of undeclared identifier 'bork'}}
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}
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