[clang] [Clang] Warn on backslash-newline-EOF (PR #97585)

[via cfe-commits]

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@@ -3183,8 +3193,31 @@ bool Lexer::LexEndOfFile(Token &Result, const char *CurPtr) {
       DiagID = diag::ext_no_newline_eof;
     }
 
-    Diag(BufferEnd, DiagID)
-      << FixItHint::CreateInsertion(EndLoc, "\n");
+    if (LastNewline.empty()) {
+      Diag(BufferEnd, DiagID) << FixItHint::CreateInsertion(EndLoc, "\n");
+    } else {
+      // While the file physically ends in a newline, the previous
+      // line might have ended in a splice, so it would be deleted
+      const char *LastSpliceLocation = LastNewline.data();
+      while (LastSpliceLocation != BufferStart &&
+             isHorizontalWhitespace(*--LastSpliceLocation))
+        ;
+
+      bool LastIsSplice = *LastSpliceLocation == '\\';
+      if (*LastSpliceLocation == '/' && LangOpts.Trigraphs)
+        // Check for "??/" trigraph for "\"
+        LastIsSplice =
+            LastSpliceLocation != BufferStart && *--LastSpliceLocation == '?' &&
+            LastSpliceLocation != BufferStart && *--LastSpliceLocation == '?';
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Sirraide wrote:

There don’t seem to be any tests for this either (and just for the record, the `*--` here is fine imo).

https://github.com/llvm/llvm-project/pull/97585