[clang-format] Reimplement InsertNewlineAtEOF (#108513)

Fixes #108333.

Author: owenca

clang/lib/Format/FormatTokenLexer.cpp

@@ -100,6 +100,13 @@ ArrayRef<FormatToken *> FormatTokenLexer::lex() {
     if (Tokens.back()->NewlinesBefore > 0 || Tokens.back()->IsMultiline)
       FirstInLineIndex = Tokens.size() - 1;
   } while (Tokens.back()->isNot(tok::eof));
+  if (Style.InsertNewlineAtEOF) {
+    auto &TokEOF = *Tokens.back();
+    if (TokEOF.NewlinesBefore == 0) {
+      TokEOF.NewlinesBefore = 1;
+      TokEOF.OriginalColumn = 0;
+    }
+  }
   return Tokens;
 }
 

clang/lib/Format/TokenAnnotator.cpp

@@ -3704,11 +3704,6 @@ void TokenAnnotator::annotate(AnnotatedLine &Line) {
   auto *First = Line.First;
   First->SpacesRequiredBefore = 1;
   First->CanBreakBefore = First->MustBreakBefore;
-
-  if (First->is(tok::eof) && First->NewlinesBefore == 0 &&
-      Style.InsertNewlineAtEOF) {
-    First->NewlinesBefore = 1;
-  }
 }
 
 // This function heuristically determines whether 'Current' starts the name of a

clang/unittests/Format/FormatTest.cpp

@@ -27577,6 +27577,12 @@ TEST_F(FormatTest, InsertNewlineAtEOF) {
 
   verifyNoChange("int i;\n", Style);
   verifyFormat("int i;\n", "int i;", Style);
+
+  constexpr StringRef Code{"namespace {\n"
+                           "int i;\n"
+                           "} // namespace"};
+  verifyFormat(Code.str() + '\n', Code, Style,
+               {tooling::Range(19, 13)}); // line 3
 }
 
 TEST_F(FormatTest, KeepEmptyLinesAtEOF) {