Suppress pedantic diagnostic for a file not ending in EOL #131794

AaronBallman · 2025-03-18T12:37:17Z

WG14 added N3411 to the list of papers which apply to older versions of C in C2y, and WG21 adopted CWG787 as a Defect Report in C++11. So we no longer should be issuing a pedantic diagnostic about a file which does not end with a newline character.

We do, however, continue to support -Wnewline-eof as an opt-in diagnostic.

WG14 added N3411 to the list of papers which apply to older versions of C, and WG21 adopted CWG787 as a Defect Report in C++11. So we no longer should be issuing a pedantic diagnostic about a file which does not end with a newline character. We do, however, continue to support -Wnewline-eof as an opt-in diagnostic.

llvmbot · 2025-03-18T12:37:51Z

@llvm/pr-subscribers-clang-tools-extra

@llvm/pr-subscribers-clangd

Author: Aaron Ballman (AaronBallman)

Changes

WG14 added N3411 to the list of papers which apply to older versions of C in C2y, and WG21 adopted CWG787 as a Defect Report in C++11. So we no longer should be issuing a pedantic diagnostic about a file which does not end with a newline character.

We do, however, continue to support -Wnewline-eof as an opt-in diagnostic.

Full diff: https://github.com/llvm/llvm-project/pull/131794.diff

6 Files Affected:

(modified) clang-tools-extra/clangd/Preamble.cpp (-1)
(modified) clang/docs/ReleaseNotes.rst (+4-1)
(modified) clang/include/clang/Basic/DiagnosticLexKinds.td (-2)
(modified) clang/lib/Lex/Lexer.cpp (+6-12)
(modified) clang/test/C/C2y/n3411.c (+2-1)
(modified) clang/test/Lexer/newline-eof.c (+10-5)

diff --git a/clang-tools-extra/clangd/Preamble.cpp b/clang-tools-extra/clangd/Preamble.cpp
index b634981bb46bd..233d827e6ed7b 100644
--- a/clang-tools-extra/clangd/Preamble.cpp
+++ b/clang-tools-extra/clangd/Preamble.cpp
@@ -628,7 +628,6 @@ buildPreamble(PathRef FileName, CompilerInvocation CI,
     switch (Info.getID()) {
     case diag::warn_no_newline_eof:
     case diag::warn_cxx98_compat_no_newline_eof:
-    case diag::ext_no_newline_eof:
       // If the preamble doesn't span the whole file, drop the no newline at
       // eof warnings.
       return Bounds.Size != ContentsBuffer->getBufferSize()
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 0adbc19f40096..71d7f9f85e739 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -128,7 +128,10 @@ C2y Feature Support
   also removes UB with code like ``(void)(void)1;``.
 - Implemented `WG14 N3411 <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3411.pdf>`_
   which allows a source file to not end with a newline character. This is still
-  reported as a conforming extension in earlier language modes.
+  reported as a conforming extension in earlier language modes. Note,
+  ``-pedantic`` will no longer diagnose this in either C or C++ modes as an
+  extension. This feature was adopted as applying to obsolete versions of C in
+  WG14 and as a defect report in WG21 (CWG787).
 - Implemented `WG14 N3353 <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3353.htm>_`
   which adds the new ``0o`` and ``0O`` ocal literal prefixes and deprecates
   octal literals other than ``0`` which do not start with the new prefix. This
diff --git a/clang/include/clang/Basic/DiagnosticLexKinds.td b/clang/include/clang/Basic/DiagnosticLexKinds.td
index bdb7e9350b5f7..cf226856864c0 100644
--- a/clang/include/clang/Basic/DiagnosticLexKinds.td
+++ b/clang/include/clang/Basic/DiagnosticLexKinds.td
@@ -52,8 +52,6 @@ def ext_multi_line_line_comment : Extension<"multi-line // comment">,
 def ext_line_comment : Extension<
   "// comments are not allowed in this language">,
   InGroup<Comment>;
-def ext_no_newline_eof : Extension<"no newline at end of file">,
-  InGroup<NewlineEOF>;
 def warn_no_newline_eof : Warning<"no newline at end of file">,
   InGroup<NewlineEOF>, DefaultIgnore;
 
diff --git a/clang/lib/Lex/Lexer.cpp b/clang/lib/Lex/Lexer.cpp
index 96d5d4f440768..fcc53f91b5728 100644
--- a/clang/lib/Lex/Lexer.cpp
+++ b/clang/lib/Lex/Lexer.cpp
@@ -3194,18 +3194,12 @@ bool Lexer::LexEndOfFile(Token &Result, const char *CurPtr) {
     SourceLocation EndLoc = getSourceLocation(BufferEnd);
     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))
-        DiagID = diag::warn_cxx98_compat_no_newline_eof;
-    } else {
-      // This is conforming in C2y, but is an extension in earlier language
-      // modes.
-      if (!LangOpts.C2y)
-        DiagID = diag::ext_no_newline_eof;
-    }
+    // 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 (LangOpts.CPlusPlus11 &&
+        !Diags.isIgnored(diag::warn_cxx98_compat_no_newline_eof, EndLoc))
+      DiagID = diag::warn_cxx98_compat_no_newline_eof;
 
     Diag(BufferEnd, DiagID) << FixItHint::CreateInsertion(EndLoc, "\n");
   }
diff --git a/clang/test/C/C2y/n3411.c b/clang/test/C/C2y/n3411.c
index 934a7c70fa67e..0fea769e30460 100644
--- a/clang/test/C/C2y/n3411.c
+++ b/clang/test/C/C2y/n3411.c
@@ -1,7 +1,8 @@
 // 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 -Wall -pedantic %s
 // RUN: %clang_cc1 -verify=good -std=c23 %s
+// RUN: %clang_cc1 -verify -Wnewline-eof -std=c23 %s
 
 /* WG14 N3411: Yes
  * Slay Some Earthly Demons XII
diff --git a/clang/test/Lexer/newline-eof.c b/clang/test/Lexer/newline-eof.c
index 9f5033384e16f..22245ac357efc 100644
--- a/clang/test/Lexer/newline-eof.c
+++ b/clang/test/Lexer/newline-eof.c
@@ -1,11 +1,16 @@
-// RUN: %clang_cc1 -fsyntax-only -Wnewline-eof -verify %s
-// RUN: %clang_cc1 -fsyntax-only -pedantic -verify %s
-// RUN: %clang_cc1 -fsyntax-only -x c++ -std=c++03 -pedantic -verify %s
-// RUN: %clang_cc1 -fsyntax-only -Wnewline-eof %s 2>&1 | FileCheck %s
+// Allowing a file to end without a newline was adopted as a Defect Report in
+// WG21 (CWG787) and in WG14 (added to the list of changes which apply to
+// earlier revisions of C in C2y). So it should not issue a pedantic diagnostic
+// in any language mode.
 
-// In C++11 mode, this is allowed, so don't warn in pedantic mode.
+// RUN: %clang_cc1 -fsyntax-only -Wnewline-eof -verify %s
+// RUN: %clang_cc1 -fsyntax-only -pedantic -verify=good %s
+// RUN: %clang_cc1 -fsyntax-only -std=c89 -pedantic -Wno-comment -verify=good %s
+// RUN: %clang_cc1 -fsyntax-only -x c++ -std=c++03 -pedantic -verify=good %s
 // RUN: %clang_cc1 -fsyntax-only -x c++ -std=c++11 -Wnewline-eof -verify %s
 // RUN: %clang_cc1 -fsyntax-only -x c++ -std=c++11 -Werror -pedantic %s
+// RUN: %clang_cc1 -fsyntax-only -Wnewline-eof %s 2>&1 | FileCheck %s
+// good-no-diagnostics
 
 // Make sure the diagnostic shows up properly at the end of the last line.
 // CHECK: newline-eof.c:[[@LINE+3]]:67

llvmbot · 2025-03-18T12:37:52Z

@llvm/pr-subscribers-clang

Author: Aaron Ballman (AaronBallman)

Changes

WG14 added N3411 to the list of papers which apply to older versions of C in C2y, and WG21 adopted CWG787 as a Defect Report in C++11. So we no longer should be issuing a pedantic diagnostic about a file which does not end with a newline character.

We do, however, continue to support -Wnewline-eof as an opt-in diagnostic.

Full diff: https://github.com/llvm/llvm-project/pull/131794.diff

6 Files Affected:

(modified) clang-tools-extra/clangd/Preamble.cpp (-1)
(modified) clang/docs/ReleaseNotes.rst (+4-1)
(modified) clang/include/clang/Basic/DiagnosticLexKinds.td (-2)
(modified) clang/lib/Lex/Lexer.cpp (+6-12)
(modified) clang/test/C/C2y/n3411.c (+2-1)
(modified) clang/test/Lexer/newline-eof.c (+10-5)

diff --git a/clang-tools-extra/clangd/Preamble.cpp b/clang-tools-extra/clangd/Preamble.cpp
index b634981bb46bd..233d827e6ed7b 100644
--- a/clang-tools-extra/clangd/Preamble.cpp
+++ b/clang-tools-extra/clangd/Preamble.cpp
@@ -628,7 +628,6 @@ buildPreamble(PathRef FileName, CompilerInvocation CI,
     switch (Info.getID()) {
     case diag::warn_no_newline_eof:
     case diag::warn_cxx98_compat_no_newline_eof:
-    case diag::ext_no_newline_eof:
       // If the preamble doesn't span the whole file, drop the no newline at
       // eof warnings.
       return Bounds.Size != ContentsBuffer->getBufferSize()
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 0adbc19f40096..71d7f9f85e739 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -128,7 +128,10 @@ C2y Feature Support
   also removes UB with code like ``(void)(void)1;``.
 - Implemented `WG14 N3411 <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3411.pdf>`_
   which allows a source file to not end with a newline character. This is still
-  reported as a conforming extension in earlier language modes.
+  reported as a conforming extension in earlier language modes. Note,
+  ``-pedantic`` will no longer diagnose this in either C or C++ modes as an
+  extension. This feature was adopted as applying to obsolete versions of C in
+  WG14 and as a defect report in WG21 (CWG787).
 - Implemented `WG14 N3353 <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3353.htm>_`
   which adds the new ``0o`` and ``0O`` ocal literal prefixes and deprecates
   octal literals other than ``0`` which do not start with the new prefix. This
diff --git a/clang/include/clang/Basic/DiagnosticLexKinds.td b/clang/include/clang/Basic/DiagnosticLexKinds.td
index bdb7e9350b5f7..cf226856864c0 100644
--- a/clang/include/clang/Basic/DiagnosticLexKinds.td
+++ b/clang/include/clang/Basic/DiagnosticLexKinds.td
@@ -52,8 +52,6 @@ def ext_multi_line_line_comment : Extension<"multi-line // comment">,
 def ext_line_comment : Extension<
   "// comments are not allowed in this language">,
   InGroup<Comment>;
-def ext_no_newline_eof : Extension<"no newline at end of file">,
-  InGroup<NewlineEOF>;
 def warn_no_newline_eof : Warning<"no newline at end of file">,
   InGroup<NewlineEOF>, DefaultIgnore;
 
diff --git a/clang/lib/Lex/Lexer.cpp b/clang/lib/Lex/Lexer.cpp
index 96d5d4f440768..fcc53f91b5728 100644
--- a/clang/lib/Lex/Lexer.cpp
+++ b/clang/lib/Lex/Lexer.cpp
@@ -3194,18 +3194,12 @@ bool Lexer::LexEndOfFile(Token &Result, const char *CurPtr) {
     SourceLocation EndLoc = getSourceLocation(BufferEnd);
     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))
-        DiagID = diag::warn_cxx98_compat_no_newline_eof;
-    } else {
-      // This is conforming in C2y, but is an extension in earlier language
-      // modes.
-      if (!LangOpts.C2y)
-        DiagID = diag::ext_no_newline_eof;
-    }
+    // 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 (LangOpts.CPlusPlus11 &&
+        !Diags.isIgnored(diag::warn_cxx98_compat_no_newline_eof, EndLoc))
+      DiagID = diag::warn_cxx98_compat_no_newline_eof;
 
     Diag(BufferEnd, DiagID) << FixItHint::CreateInsertion(EndLoc, "\n");
   }
diff --git a/clang/test/C/C2y/n3411.c b/clang/test/C/C2y/n3411.c
index 934a7c70fa67e..0fea769e30460 100644
--- a/clang/test/C/C2y/n3411.c
+++ b/clang/test/C/C2y/n3411.c
@@ -1,7 +1,8 @@
 // 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 -Wall -pedantic %s
 // RUN: %clang_cc1 -verify=good -std=c23 %s
+// RUN: %clang_cc1 -verify -Wnewline-eof -std=c23 %s
 
 /* WG14 N3411: Yes
  * Slay Some Earthly Demons XII
diff --git a/clang/test/Lexer/newline-eof.c b/clang/test/Lexer/newline-eof.c
index 9f5033384e16f..22245ac357efc 100644
--- a/clang/test/Lexer/newline-eof.c
+++ b/clang/test/Lexer/newline-eof.c
@@ -1,11 +1,16 @@
-// RUN: %clang_cc1 -fsyntax-only -Wnewline-eof -verify %s
-// RUN: %clang_cc1 -fsyntax-only -pedantic -verify %s
-// RUN: %clang_cc1 -fsyntax-only -x c++ -std=c++03 -pedantic -verify %s
-// RUN: %clang_cc1 -fsyntax-only -Wnewline-eof %s 2>&1 | FileCheck %s
+// Allowing a file to end without a newline was adopted as a Defect Report in
+// WG21 (CWG787) and in WG14 (added to the list of changes which apply to
+// earlier revisions of C in C2y). So it should not issue a pedantic diagnostic
+// in any language mode.
 
-// In C++11 mode, this is allowed, so don't warn in pedantic mode.
+// RUN: %clang_cc1 -fsyntax-only -Wnewline-eof -verify %s
+// RUN: %clang_cc1 -fsyntax-only -pedantic -verify=good %s
+// RUN: %clang_cc1 -fsyntax-only -std=c89 -pedantic -Wno-comment -verify=good %s
+// RUN: %clang_cc1 -fsyntax-only -x c++ -std=c++03 -pedantic -verify=good %s
 // RUN: %clang_cc1 -fsyntax-only -x c++ -std=c++11 -Wnewline-eof -verify %s
 // RUN: %clang_cc1 -fsyntax-only -x c++ -std=c++11 -Werror -pedantic %s
+// RUN: %clang_cc1 -fsyntax-only -Wnewline-eof %s 2>&1 | FileCheck %s
+// good-no-diagnostics
 
 // Make sure the diagnostic shows up properly at the end of the last line.
 // CHECK: newline-eof.c:[[@LINE+3]]:67

clang/test/Lexer/newline-eof.c

clang/docs/ReleaseNotes.rst

clang/lib/Lex/Lexer.cpp

Note: I wasn't able to run the python script to regenerate the cxx_dr_status.html page due to encoding errors, so that still needs to be run.

Review comments pointed out that this is no longer a necessary diagnostic given that C++11 adopted the change as a defect report.

Endilll

cxx_dr_status.html entry should be updated, too.
It will be trivial to do once #131812 is merged.

clang/test/CXX/drs/cwg787.cpp

zygoloid

LG

clang-tools-extra/clangd/Preamble.cpp

clang/docs/ReleaseNotes.rst

Endilll · 2025-03-18T21:47:39Z

Both #131812 and #131816 have been merged, so you can update your branch and run the script now.

AaronBallman · 2025-03-19T11:49:08Z

Both #131812 and #131816 have been merged, so you can update your branch and run the script now.

Thank you! I re-ran the script and it seems to have an issue with line endings because the diff shows changes on every line in the file. I'm going to land these changes as-is, the script can be fixed up and list regenerated in a follow-up.

AaronBallman added c c++ clang:diagnostics New/improved warning or error message in Clang, but not in clang-tidy or static analyzer labels Mar 18, 2025

AaronBallman requested review from zygoloid, cor3ntin, erichkeane and Sirraide March 18, 2025 12:37

llvmbot added clang Clang issues not falling into any other category clang-tools-extra clangd clang:frontend Language frontend issues, e.g. anything involving "Sema" labels Mar 18, 2025

cor3ntin reviewed Mar 18, 2025

View reviewed changes

clang/test/Lexer/newline-eof.c Show resolved Hide resolved

erichkeane reviewed Mar 18, 2025

View reviewed changes

clang/docs/ReleaseNotes.rst Outdated Show resolved Hide resolved

clang/lib/Lex/Lexer.cpp Outdated Show resolved Hide resolved

Add C++ DR test

c7568b7

Note: I wasn't able to run the python script to regenerate the cxx_dr_status.html page due to encoding errors, so that still needs to be run.

AaronBallman requested a review from Endilll as a code owner March 18, 2025 13:17

AaronBallman added 2 commits March 18, 2025 09:18

Update release notes

e7ce604

Remove the C++98 compat diagnostic

754cfab

Review comments pointed out that this is no longer a necessary diagnostic given that C++11 adopted the change as a defect report.

erichkeane approved these changes Mar 18, 2025

View reviewed changes

Fix build error

fcee196

Endilll reviewed Mar 18, 2025

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clang/test/CXX/drs/cwg787.cpp Outdated Show resolved Hide resolved

Update DR test based on review feedback

c8337b3

zygoloid reviewed Mar 18, 2025

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clang/docs/ReleaseNotes.rst Outdated Show resolved Hide resolved

Update based on review feedback

42ca9cb

Sirraide approved these changes Mar 18, 2025

View reviewed changes

AaronBallman merged commit 449cdfa into llvm:main Mar 19, 2025
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AaronBallman deleted the aballman-newline-eol-pedantic branch March 19, 2025 11:49

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Suppress pedantic diagnostic for a file not ending in EOL #131794

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Suppress pedantic diagnostic for a file not ending in EOL #131794

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