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1826842865
This patch implements an extension to the preprocessor: __VA_OPT__(contents) --> which expands into its contents if variadic arguments are supplied to the parent macro, or behaves as an empty token if none. - Currently this feature is only enabled for C++2a (this could be enabled, with some careful tweaks, for other dialects with the appropriate extension or compatibility warnings) - The patch was reviewed here: https://reviews.llvm.org/D35782 and asides from the above (and moving some of the definition and expansion recognition logic into the corresponding state machines), I believe I incorporated all of Richard's suggestions. A few technicalities (most of which were clarified through private correspondence between rsmith, hubert and thomas) are worth mentioning. Given: #define F(a,...) a #__VA_OPT__(a ## a) a ## __VA_OPT__(__VA_ARGS__) - The call F(,) Does not supply any tokens for the variadic arguments and hence VA_OPT behaves as a placeholder. - When expanding VA_OPT (for e.g. F(,1) token pasting occurs eagerly within its contents if the contents need to be stringified. - A hash or a hashhash prior to VA_OPT does not inhibit expansion of arguments if they are the first token within VA_OPT. - When a variadic argument is supplied, argument substitution occurs within the contents as does stringification - and these resulting tokens are inserted back into the macro expansions token stream just prior to the entire stream being rescanned and concatenated. See wg21.link/P0306 for further details on the feature. Acknowledgment: This patch would have been poorer if not for Richard Smith's usual thoughtful analysis and feedback. llvm-svn: 315840
65 lines
1.5 KiB
C++
65 lines
1.5 KiB
C++
// RUN: %clang_cc1 %s -Eonly -verify -Wno-all -pedantic -std=c++2a
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//expected-error@+1{{missing '('}}
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#define V1(...) __VA_OPT__
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#undef V1
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// OK
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#define V1(...) __VA_OPT__ ()
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#undef V1
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//expected-warning@+1{{can only appear in the expansion of a variadic macro}}
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#define V2() __VA_OPT__(x)
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#undef V2
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//expected-error@+2{{missing ')' after}}
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//expected-note@+1{{to match this '('}}
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#define V3(...) __VA_OPT__(
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#undef V3
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#define V4(...) __VA_OPT__(__VA_ARGS__)
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#undef V4
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//expected-error@+1{{nested}}
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#define V5(...) __VA_OPT__(__VA_OPT__())
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#undef V5
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//expected-error@+1{{not followed by}}
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#define V1(...) __VA_OPT__ (#)
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#undef V1
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//expected-error@+1{{cannot appear at start}}
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#define V1(...) __VA_OPT__ (##)
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#undef V1
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//expected-error@+1{{cannot appear at start}}
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#define V1(...) __VA_OPT__ (## X) x
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#undef V1
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//expected-error@+1{{cannot appear at end}}
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#define V1(...) y __VA_OPT__ (X ##)
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#undef V1
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#define FOO(x,...) # __VA_OPT__(x) #x #__VA_OPT__(__VA_ARGS__) //OK
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//expected-error@+1{{not followed by a macro parameter}}
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#define V1(...) __VA_OPT__(#)
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#undef V1
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//expected-error@+1{{cannot appear at start}}
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#define V1(...) a __VA_OPT__(##) b
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#undef V1
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//expected-error@+1{{cannot appear at start}}
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#define V1(...) a __VA_OPT__(a ## b) b __VA_OPT__(##)
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#undef V1
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#define V1(x,...) # __VA_OPT__(b x) // OK
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#undef V1
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//expected-error@+2{{missing ')' after}}
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//expected-note@+1{{to match this '('}}
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#define V1(...) __VA_OPT__ ((())
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#undef V1
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