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[C2y] Implement WG14 N3411 #130180

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Merged
merged 2 commits into from
Mar 7, 2025
Merged

[C2y] Implement WG14 N3411 #130180

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517b2b6
[C2y] Implement WG14 N3411
AaronBallman Mar 6, 2025
de2a448
Add a test case based on review feedback
AaronBallman Mar 7, 2025
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3 changes: 3 additions & 0 deletions clang/docs/ReleaseNotes.rst
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Expand Up @@ -108,6 +108,9 @@ C Language Changes

C2y Feature Support
^^^^^^^^^^^^^^^^^^^
- Implemented N3411 which allows a source file to not end with a newline
character. This is still reported as a conforming extension in earlier
language modes.

C23 Feature Support
^^^^^^^^^^^^^^^^^^^
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15 changes: 7 additions & 8 deletions clang/lib/Lex/Lexer.cpp
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Expand Up @@ -3192,23 +3192,22 @@ bool Lexer::LexEndOfFile(Token &Result, const char *CurPtr) {
if (CurPtr != BufferStart && (CurPtr[-1] != '\n' && CurPtr[-1] != '\r')) {
DiagnosticsEngine &Diags = PP->getDiagnostics();
SourceLocation EndLoc = getSourceLocation(BufferEnd);
unsigned DiagID;
unsigned DiagID = diag::warn_no_newline_eof;

if (LangOpts.CPlusPlus11) {
// C++11 [lex.phases] 2.2 p2
// Prefer the C++98 pedantic compatibility warning over the generic,
// non-extension, user-requested "missing newline at EOF" warning.
if (!Diags.isIgnored(diag::warn_cxx98_compat_no_newline_eof, EndLoc)) {
if (!Diags.isIgnored(diag::warn_cxx98_compat_no_newline_eof, EndLoc))
DiagID = diag::warn_cxx98_compat_no_newline_eof;
} else {
DiagID = diag::warn_no_newline_eof;
}
} else {
DiagID = diag::ext_no_newline_eof;
// This is conforming in C2y, but is an extension in earlier language
// modes.
if (!LangOpts.C2y)
DiagID = diag::ext_no_newline_eof;
Comment on lines +3204 to +3207
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I found that the corresponding change in C++ was introduced by a CWG issue (CWG787). Would it be preferred to treat N3411 as a DR?

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Nope, WG14 has a list of such things and this paper isn't on the list: https://www.open-std.org/jtc1/sc22/wg14/www/previous.html

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Interestingly, GCC does not warn https://compiler-explorer.com/z/vWMf6W551 , so I question the value of bundling that warning in -fpedantic.

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-pedantic exists to diagnose extensions and this is definitively an extension. So that's a GCC bug IMO. :-)

}

Diag(BufferEnd, DiagID)
<< FixItHint::CreateInsertion(EndLoc, "\n");
Diag(BufferEnd, DiagID) << FixItHint::CreateInsertion(EndLoc, "\n");
}

BufferPtr = CurPtr;
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15 changes: 15 additions & 0 deletions clang/test/C/C2y/n3411.c
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@@ -0,0 +1,15 @@
// RUN: %clang_cc1 -verify=good -std=c2y -Wall -pedantic %s
// RUN: %clang_cc1 -verify -Wnewline-eof -std=c2y -Wall -pedantic %s
// RUN: %clang_cc1 -verify -std=c23 -Wall -pedantic %s
// RUN: %clang_cc1 -verify=good -std=c23 %s

/* WG14 N3411: Yes
* Slay Some Earthly Demons XII
*
* Allow a non-empty source file to end without a final newline character. Note
* that this file intentionally does not end with a trailing newline.
*/
// good-no-diagnostics

int x; // Ensure the file contains at least one declaration.
// expected-warning {{no newline at end of file}}
2 changes: 1 addition & 1 deletion clang/www/c_status.html
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Expand Up @@ -294,7 +294,7 @@ <h2 id="c2y">C2y implementation status</h2>
<tr>
<td>Slay Some Earthly Demons XII</td>
<td><a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3411.pdf">N3411</a></td>
<td class="unknown" align="center">Unknown</td>
<td class="unreleased" align="center">Clang 21</td>
</tr>
<tr>
<td>Slay Some Earthly Demons XIII</td>
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