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[c++20] Implement tweaked __VA_OPT__ rules from P1042R1: 

* __VA_OPT__ is expanded if the *expanded* __VA_ARGS__ is non-empty,
   not if the original argument contained no tokens.
 * Placemarkers at the start and end of __VA_OPT__ are retained just
   long enough to paste them with adjacent ## operators. We never paste
   "across" a discarded placemarker.

llvm-svn: 359964
This commit is contained in:
Richard Smith 2019-05-04 06:46:18 +00:00
parent 5ddd564e19
commit cb1beee76f
7 changed files with 116 additions and 24 deletions
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13
clang/include/clang/Lex/MacroArgs.h
View File

@ -112,18 +112,19 @@ public:
bool isVarargsElidedUse() const { return VarargsElided; }
/// Returns true if the macro was defined with a variadic (ellipsis) parameter
/// AND was invoked with at least one token supplied as a variadic argument.
/// AND was invoked with at least one token supplied as a variadic argument
/// (after pre-expansion).
///
/// \code
/// #define F(a) a
/// #define V(a, ...) __VA_OPT__(a)
/// F() <-- returns false on this invocation.
/// V(,a) <-- returns true on this invocation.
/// V(,) <-- returns false on this invocation.
/// F() <-- returns false on this invocation.
/// V(,a) <-- returns true on this invocation.
/// V(,) <-- returns false on this invocation.
/// V(,F()) <-- returns false on this invocation.
/// \endcode
///
bool invokedWithVariadicArgument(const MacroInfo *const MI) const;
bool invokedWithVariadicArgument(const MacroInfo *const MI, Preprocessor &PP);
/// StringifyArgument - Implement C99 6.10.3.2p2, converting a sequence of
/// tokens into the literal string token that should be produced by the C #

26
clang/include/clang/Lex/VariadicMacroSupport.h
View File

@ -113,6 +113,8 @@ namespace clang {
UnmatchedOpeningParens.push_back(LParenLoc);
}
/// Are we at the top level within the __VA_OPT__?
bool isAtTopLevel() const { return UnmatchedOpeningParens.size() == 1; }
};
/// A class for tracking whether we're inside a VA_OPT during a
@ -135,7 +137,8 @@ namespace clang {
unsigned StringifyBefore : 1;
unsigned CharifyBefore : 1;
unsigned BeginsWithPlaceholder : 1;
unsigned EndsWithPlaceholder : 1;
bool hasStringifyBefore() const {
assert(!isReset() &&
@ -151,7 +154,8 @@ namespace clang {
public:
VAOptExpansionContext(Preprocessor &PP)
: VAOptDefinitionContext(PP), LeadingSpaceForStringifiedToken(false),
StringifyBefore(false), CharifyBefore(false) {
StringifyBefore(false), CharifyBefore(false),
BeginsWithPlaceholder(false), EndsWithPlaceholder(false) {
SyntheticEOFToken.startToken();
SyntheticEOFToken.setKind(tok::eof);
}
@ -162,6 +166,8 @@ namespace clang {
LeadingSpaceForStringifiedToken = false;
StringifyBefore = false;
CharifyBefore = false;
BeginsWithPlaceholder = false;
EndsWithPlaceholder = false;
}
const Token &getEOFTok() const { return SyntheticEOFToken; }
@ -174,8 +180,24 @@ namespace clang {
LeadingSpaceForStringifiedToken = HasLeadingSpace;
}
void hasPlaceholderAfterHashhashAtStart() { BeginsWithPlaceholder = true; }
void hasPlaceholderBeforeRParen() {
if (isAtTopLevel())
EndsWithPlaceholder = true;
}
bool beginsWithPlaceholder() const {
assert(!isReset() &&
"Must only be called if the state has not been reset");
return BeginsWithPlaceholder;
}
bool endsWithPlaceholder() const {
assert(!isReset() &&
"Must only be called if the state has not been reset");
return EndsWithPlaceholder;
}
bool hasCharifyBefore() const {
assert(!isReset() &&
"Must only be called if the state has not been reset");

9
clang/lib/Lex/MacroArgs.cpp
View File

@ -135,15 +135,12 @@ const Token *MacroArgs::getUnexpArgument(unsigned Arg) const {
return Result;
}
// This function assumes that the variadic arguments are the tokens
// corresponding to the last parameter (ellipsis) - and since tokens are
// separated by the 'eof' token, if that is the only token corresponding to that
// last parameter, we know no variadic arguments were supplied.
bool MacroArgs::invokedWithVariadicArgument(const MacroInfo *const MI) const {
bool MacroArgs::invokedWithVariadicArgument(const MacroInfo *const MI,
Preprocessor &PP) {
if (!MI->isVariadic())
return false;
const int VariadicArgIndex = getNumMacroArguments() - 1;
return getUnexpArgument(VariadicArgIndex)->isNot(tok::eof);
return getPreExpArgument(VariadicArgIndex, PP).front().isNot(tok::eof);
}
/// ArgNeedsPreexpansion - If we can prove that the argument won't be affected

52
clang/lib/Lex/TokenLexer.cpp
View File

@ -243,8 +243,7 @@ void TokenLexer::ExpandFunctionArguments() {
// we install the newly expanded sequence as the new 'Tokens' list.
bool MadeChange = false;
const bool CalledWithVariadicArguments =
ActualArgs->invokedWithVariadicArgument(Macro);
Optional<bool> CalledWithVariadicArguments;
VAOptExpansionContext VCtx(PP);
@ -291,7 +290,12 @@ void TokenLexer::ExpandFunctionArguments() {
// this token. Note sawClosingParen() returns true only if the r_paren matches
// the closing r_paren of the __VA_OPT__.
if (!Tokens[I].is(tok::r_paren) || !VCtx.sawClosingParen()) {
if (!CalledWithVariadicArguments) {
// Lazily expand __VA_ARGS__ when we see the first __VA_OPT__.
if (!CalledWithVariadicArguments.hasValue()) {
CalledWithVariadicArguments =
ActualArgs->invokedWithVariadicArgument(Macro, PP);
}
if (!*CalledWithVariadicArguments) {
// Skip this token.
continue;
}
@ -314,8 +318,8 @@ void TokenLexer::ExpandFunctionArguments() {
stringifyVAOPTContents(ResultToks, VCtx,
/*ClosingParenLoc*/ Tokens[I].getLocation());
} else if (/*No tokens within VAOPT*/ !(
ResultToks.size() - VCtx.getNumberOfTokensPriorToVAOpt())) {
} else if (/*No tokens within VAOPT*/
ResultToks.size() == VCtx.getNumberOfTokensPriorToVAOpt()) {
// Treat VAOPT as a placemarker token. Eat either the '##' before the
// RHS/VAOPT (if one exists, suggesting that the LHS (if any) to that
// hashhash was not a placemarker) or the '##'
@ -326,6 +330,26 @@ void TokenLexer::ExpandFunctionArguments() {
} else if ((I + 1 != E) && Tokens[I + 1].is(tok::hashhash)) {
++I; // Skip the following hashhash.
}
} else {
// If there's a ## before the __VA_OPT__, we might have discovered
// that the __VA_OPT__ begins with a placeholder. We delay action on
// that to now to avoid messing up our stashed count of tokens before
// __VA_OPT__.
if (VCtx.beginsWithPlaceholder()) {
assert(VCtx.getNumberOfTokensPriorToVAOpt() > 0 &&
ResultToks.size() >= VCtx.getNumberOfTokensPriorToVAOpt() &&
ResultToks[VCtx.getNumberOfTokensPriorToVAOpt() - 1].is(
tok::hashhash) &&
"no token paste before __VA_OPT__");
ResultToks.erase(ResultToks.begin() +
VCtx.getNumberOfTokensPriorToVAOpt() - 1);
}
// If the expansion of __VA_OPT__ ends with a placeholder, eat any
// following '##' token.
if (VCtx.endsWithPlaceholder() && I + 1 != E &&
Tokens[I + 1].is(tok::hashhash)) {
++I;
}
}
VCtx.reset();
// We processed __VA_OPT__'s closing paren (and the exit out of
@ -386,6 +410,7 @@ void TokenLexer::ExpandFunctionArguments() {
!ResultToks.empty() && ResultToks.back().is(tok::hashhash);
bool PasteBefore = I != 0 && Tokens[I-1].is(tok::hashhash);
bool PasteAfter = I+1 != E && Tokens[I+1].is(tok::hashhash);
bool RParenAfter = I+1 != E && Tokens[I+1].is(tok::r_paren);
assert((!NonEmptyPasteBefore || PasteBefore || VCtx.isInVAOpt()) &&
"unexpected ## in ResultToks");
@ -470,6 +495,18 @@ void TokenLexer::ExpandFunctionArguments() {
NextTokGetsSpace);
ResultToks[FirstResult].setFlagValue(Token::StartOfLine, false);
NextTokGetsSpace = false;
} else {
// We're creating a placeholder token. Usually this doesn't matter,
// but it can affect paste behavior when at the start or end of a
// __VA_OPT__.
if (NonEmptyPasteBefore) {
// We're imagining a placeholder token is inserted here. If this is
// the first token in a __VA_OPT__ after a ##, delete the ##.
assert(VCtx.isInVAOpt() && "should only happen inside a __VA_OPT__");
VCtx.hasPlaceholderAfterHashhashAtStart();
}
if (RParenAfter)
VCtx.hasPlaceholderBeforeRParen();
}
continue;
}
@ -534,6 +571,9 @@ void TokenLexer::ExpandFunctionArguments() {
continue;
}
if (RParenAfter)
VCtx.hasPlaceholderBeforeRParen();
// If this is on the RHS of a paste operator, we've already copied the
// paste operator to the ResultToks list, unless the LHS was empty too.
// Remove it.
@ -547,6 +587,8 @@ void TokenLexer::ExpandFunctionArguments() {
if (!VCtx.isInVAOpt() ||
ResultToks.size() > VCtx.getNumberOfTokensPriorToVAOpt())
ResultToks.pop_back();
else
VCtx.hasPlaceholderAfterHashhashAtStart();
}
// If this is the __VA_ARGS__ token, and if the argument wasn't provided,

8
clang/test/Preprocessor/macro_vaopt_expand.cpp
View File

@ -129,8 +129,8 @@
#define G(a,...) __VA_OPT__(B a) ## 1
26: F(,1)
26_1: G(,1)
// CHECK: 26: B1
// CHECK: 26_1: B1
// CHECK: 26: B 1
// CHECK: 26_1: B 1
#undef F
#undef G
@ -140,9 +140,9 @@
27: F(,1)
27_1: F(A0,1)
28: G(,1)
// CHECK: 27: B11
// CHECK: 27: B 11
// CHECK: 27_1: BexpandedA0 11
// CHECK: 28: B11
// CHECK: 28: B 11
#undef F
#undef G

30
clang/test/Preprocessor/macro_vaopt_p1042r1.cpp Normal file
View File

@ -0,0 +1,30 @@
RUN: %clang_cc1 -E %s -pedantic -std=c++2a | FileCheck -strict-whitespace %s
#define LPAREN() (
#define G(Q) 42
#define F1(R, X, ...) __VA_OPT__(G R X) )
1: int x = F1(LPAREN(), 0, <:-);
// CHECK: 1: int x = 42;
#define F2(...) f(0 __VA_OPT__(,) __VA_ARGS__)
#define EMP
2: F2(EMP)
// CHECK: 2: f(0 )
#define H3(X, ...) #__VA_OPT__(X##X X##X)
3: H3(, 0)
// CHECK: 3: ""
#define H4(X, ...) __VA_OPT__(a X ## X) ## b
4: H4(, 1)
// CHECK: 4: a b
#define H4B(X, ...) a ## __VA_OPT__(X ## X b)
4B: H4B(, 1)
// CHECK: 4B: a b
#define H5A(...) __VA_OPT__()/**/__VA_OPT__()
#define H5B(X) a ## X ## b
#define H5C(X) H5B(X)
5: H5C(H5A())
// CHECK: 5: ab

2
clang/www/cxx_status.html
View File

@ -858,7 +858,7 @@ as the draft C++2a standard evolves.
</tr>
<tr> <!-- from Rapperswil -->
<td><a href="http://wg21.link/p1042r1">P1042R1</a></td>
<td class="partial" align="center">Partial</td>
<td class="svn" align="center">SVN</td>
</tr>
<tr>
<td>Designated initializers</td>