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[clang-format] Handle Trailing Whitespace After Line Continuation (P2223R2) (#145243)

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Fixes #145226.

Implement
[P2223R2](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2223r2.pdf)
in clang-format to correctly handle cases where a backslash '\\' is
followed by trailing whitespace before the newline.
Previously, `clang-format` failed to properly detect and handle such
cases, leading to misformatted code.

With this, `clang-format` matches the behavior already implemented in
Clang's lexer and `DependencyDirectivesScanner.cpp`, which allow
trailing whitespace after a line continuation in any C++ standard.
This commit is contained in:
Naveen Seth Hanig
2025-06-25 09:13:00 -07:00
committed by GitHub
parent 9a7720ad2f
commit dd47b845a6
2 changed files with 36 additions and 9 deletions
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30
clang/lib/Format/FormatTokenLexer.cpp
View File

@@ -14,6 +14,7 @@
#include "FormatTokenLexer.h"
#include "FormatToken.h"
#include "clang/Basic/CharInfo.h"
#include "clang/Basic/SourceLocation.h"
#include "clang/Basic/SourceManager.h"
#include "clang/Format/Format.h"
@@ -1203,16 +1204,22 @@ static size_t countLeadingWhitespace(StringRef Text) {
const unsigned char *const End = Text.bytes_end();
const unsigned char *Cur = Begin;
while (Cur < End) {
if (isspace(Cur[0])) {
if (isWhitespace(Cur[0])) {
++Cur;
} else if (Cur[0] == '\\' && (Cur[1] == '\n' || Cur[1] == '\r')) {
// A '\' followed by a newline always escapes the newline, regardless
// of whether there is another '\' before it.
} else if (Cur[0] == '\\') {
// A backslash followed by optional horizontal whitespaces (P22232R2) and
// then a newline always escapes the newline.
// The source has a null byte at the end. So the end of the entire input
// isn't reached yet. Also the lexer doesn't break apart an escaped
// newline.
assert(End - Cur >= 2);
Cur += 2;
const auto *Lookahead = Cur + 1;
while (isHorizontalWhitespace(*Lookahead))
++Lookahead;
// No line splice found; the backslash is a token.
if (!isVerticalWhitespace(*Lookahead))
break;
// Splice found, consume it.
Cur = Lookahead + 1;
} else if (Cur[0] == '?' && Cur[1] == '?' && Cur[2] == '/' &&
(Cur[3] == '\n' || Cur[3] == '\r')) {
// Newlines can also be escaped by a '?' '?' '/' trigraph. By the way, the
@@ -1295,13 +1302,18 @@ FormatToken *FormatTokenLexer::getNextToken() {
case '/':
// The text was entirely whitespace when this loop was entered. Thus
// this has to be an escape sequence.
assert(Text.substr(i, 2) == "\\\r" || Text.substr(i, 2) == "\\\n" ||
Text.substr(i, 4) == "\?\?/\r" ||
assert(Text.substr(i, 4) == "\?\?/\r" ||
Text.substr(i, 4) == "\?\?/\n" ||
(i >= 1 && (Text.substr(i - 1, 4) == "\?\?/\r" ||
Text.substr(i - 1, 4) == "\?\?/\n")) ||
(i >= 2 && (Text.substr(i - 2, 4) == "\?\?/\r" ||
Text.substr(i - 2, 4) == "\?\?/\n")));
Text.substr(i - 2, 4) == "\?\?/\n")) ||
(Text[i] == '\\' && [&]() -> bool {
size_t j = i + 1;
while (j < Text.size() && isHorizontalWhitespace(Text[j]))
++j;
return j < Text.size() && (Text[j] == '\n' || Text[j] == '\r');
}()));
InEscape = true;
break;
default:

15
clang/unittests/Format/FormatTest.cpp
View File

@@ -25768,6 +25768,21 @@ TEST_F(FormatTest, OperatorPassedAsAFunctionPtr) {
verifyFormat("foo(operator, , -42);", Style);
}
TEST_F(FormatTest, LineSpliceWithTrailingWhitespace) {
auto Style = getLLVMStyle();
Style.AlignEscapedNewlines = FormatStyle::ENAS_DontAlign;
Style.UseTab = FormatStyle::UT_Never;
verifyFormat("int i;", " \\ \n"
" int i;");
verifyFormat("#define FOO(args) \\\n"
" struct a {};",
"#define FOO( args ) \\ \n"
"struct a{\\\t\t\t\n"
" };",
Style);
}
TEST_F(FormatTest, WhitespaceSensitiveMacros) {
FormatStyle Style = getLLVMStyle();
Style.WhitespaceSensitiveMacros.push_back("FOO");