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Enforce a couple of char literal restrictions from #1964: (#5960)

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* `\x` escapes are not permitted in character literals
* ASCII control characters (U+0000 .. U+001F) are not permitted in
character literals unless specified with escape sequences.
This commit is contained in:
Richard Smith
2025-08-15 00:45:16 +00:00
committed by GitHub
parent ae54873441
commit 7727c62880
6 changed files with 110 additions and 40 deletions
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toolchain/lex/string_literal.cpp
+34 -1
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@@ -434,6 +434,8 @@ static auto ExpandEscapeSequencesAndRemoveIndent(
break;
}
// TODO: Also reject vertical whitespace other than \n, but ignore a \r
// before a \n.
if (IsHorizontalWhitespace(contents.front())) {
// Horizontal whitespace other than ` ` is valid only at the end of a
// line.
@@ -476,6 +478,11 @@ static auto ExpandEscapeSequencesAndRemoveIndent(
}
}
// Returns whether the given character is a control character.
static auto IsControlCharacter(llvm::UTF32 c) -> bool {
return (c >= 0 && c <= 0x1F) || (c >= 0x7F && c <= 0x9F);
}
auto StringLiteral::ComputeCharLiteralValue(
Diagnostics::Emitter<const char*>& emitter) const
-> std::optional<CharLiteralValue> {
@@ -516,7 +523,33 @@ auto StringLiteral::ComputeCharLiteralValue(
emitter.Emit(text_.begin(), CharLiteralEmpty);
return std::nullopt;
}
return CharLiteralValue{.value = static_cast<int32_t>(target[0])};
auto result = target[0];
// Check for a control character that's not written as an escape sequence.
// Also don't diagnose horizontal whitespace, because that was already
// done by ExpandEscapeSequencesAndRemoveIndent.
if (IsControlCharacter(result) && content_.front() != '\\' &&
!IsHorizontalWhitespace(content_.front())) {
// TODO: Suggest \0 instead of \u{00} for a NUL character.
CARBON_DIAGNOSTIC(CharLiteralControlCharacter, Error,
"control character in character literal; specify as "
"escape sequence `\\u{{{0:X-2}}`",
llvm::UTF32);
emitter.Emit(text_.begin(), CharLiteralControlCharacter, result);
return std::nullopt;
}
if (content_.starts_with("\\x")) {
CARBON_DIAGNOSTIC(CharLiteralHexEscape, Error,
"escape sequence `\\x` in character literal; specify "
"as escape sequence `\\u{{{0:X-2}}`",
llvm::UTF32);
emitter.Emit(text_.begin(), CharLiteralHexEscape, result);
return std::nullopt;
}
return CharLiteralValue{.value = static_cast<int32_t>(result)};
}
case llvm::sourceExhausted: {
CARBON_DIAGNOSTIC(CharLiteralUnderflow, Error, "incomplete UTF-8");