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

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.

Author: AaronBallman

clang-tools-extra/clangd/Preamble.cpp

@@ -627,10 +627,8 @@ buildPreamble(PathRef FileName, CompilerInvocation CI,
       return DiagnosticsEngine::Ignored;
     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.
+      // eof warning.
       return Bounds.Size != ContentsBuffer->getBufferSize()
                  ? DiagnosticsEngine::Level::Ignored
                  : DiagLevel;

clang/docs/ReleaseNotes.rst

@@ -130,8 +130,10 @@ C2y Feature Support
   that ``_Generic`` selection associations may now have ``void`` type, but it
   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.
+  which allows a source file to not end with a newline character. Note,
+  ``-pedantic`` will no longer diagnose this in either C or C++ modes. 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

clang/include/clang/Basic/DiagnosticLexKinds.td

@@ -52,15 +52,9 @@ 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;
 
-def warn_cxx98_compat_no_newline_eof : Warning<
-  "C++98 requires newline at end of file">,
-  InGroup<CXX98CompatPedantic>, DefaultIgnore;
-
 def ext_dollar_in_identifier : Extension<"'$' in identifier">,
   InGroup<DiagGroup<"dollar-in-identifier-extension">>;
 def ext_charize_microsoft : Extension<

clang/lib/Lex/Lexer.cpp

@@ -3187,28 +3187,12 @@ bool Lexer::LexEndOfFile(Token &Result, const char *CurPtr) {
     ConditionalStack.pop_back();
   }
 
-  // C99 5.1.1.2p2: If the file is non-empty and didn't end in a newline, issue
-  // a pedwarn.
-  if (CurPtr != BufferStart && (CurPtr[-1] != '\n' && CurPtr[-1] != '\r')) {
-    DiagnosticsEngine &Diags = PP->getDiagnostics();
-    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;
-    }
-
-    Diag(BufferEnd, DiagID) << FixItHint::CreateInsertion(EndLoc, "\n");
-  }
+  // Before C++11 and C2y, a file not ending with a newline was UB. Both
+  // standards changed this behavior (as a DR or equivalent), but we still have
+  // an opt-in diagnostic to warn about it.
+  if (CurPtr != BufferStart && (CurPtr[-1] != '\n' && CurPtr[-1] != '\r'))
+    Diag(BufferEnd, diag::warn_no_newline_eof)
+        << FixItHint::CreateInsertion(getSourceLocation(BufferEnd), "\n");
 
   BufferPtr = CurPtr;
 

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

clang/test/CXX/drs/cwg787.cpp

@@ -0,0 +1,13 @@
+// RUN: %clang_cc1 -triple %itanium_abi_triple -std=c++98 %s -verify -fexceptions -fcxx-exceptions -pedantic-errors
+// RUN: %clang_cc1 -triple %itanium_abi_triple -std=c++11 %s -verify -fexceptions -fcxx-exceptions -pedantic-errors
+// RUN: %clang_cc1 -triple %itanium_abi_triple -std=c++14 %s -verify -fexceptions -fcxx-exceptions -pedantic-errors
+// RUN: %clang_cc1 -triple %itanium_abi_triple -std=c++17 %s -verify -fexceptions -fcxx-exceptions -pedantic-errors
+// RUN: %clang_cc1 -triple %itanium_abi_triple -std=c++20 %s -verify -fexceptions -fcxx-exceptions -pedantic-errors
+// RUN: %clang_cc1 -triple %itanium_abi_triple -std=c++23 %s -verify -fexceptions -fcxx-exceptions -pedantic-errors
+// RUN: %clang_cc1 -triple %itanium_abi_triple -std=c++2c %s -verify -fexceptions -fcxx-exceptions -pedantic-errors
+// expected-no-diagnostics
+
+// This file intentionally does not end with a newline. CWG787 made this
+// well-defined behavior.
+
+// cwg787: 21

clang/test/Lexer/newline-eof-c++98-compat.cpp

@@ -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