[clang] Avoid suggesting typoed directives in .S files

This patch is itended to avoid suggesting typoed directives in `.S`
files to support the cases of `#` directives treated as comments or
various pseudo-ops. The feature is implemented in
https://reviews.llvm.org/D124726.

Fixes: https://reviews.llvm.org/D124726#3516346.

Reviewed By: nickdesaulniers

Differential Revision: https://reviews.llvm.org/D125727

clang/lib/Lex/PPDirectives.cpp

@@ -481,6 +481,10 @@ Optional<unsigned> Preprocessor::getSkippedRangeForExcludedConditionalBlock(
 void Preprocessor::SuggestTypoedDirective(const Token &Tok,
                                           StringRef Directive,
                                           const SourceLocation &EndLoc) const {
+  // If this is a `.S` file, treat unknown # directives as non-preprocessor
+  // directives.
+  if (getLangOpts().AsmPreprocessor) return;
+
   std::vector<StringRef> Candidates = {
       "if", "ifdef", "ifndef", "elif", "else", "endif"
   };

clang/test/Preprocessor/suggest-typoed-directive.S

@@ -0,0 +1,29 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+// expected-no-diagnostics
+
+#ifdef UNDEFINED
+#id
+#ifd
+#ifde
+#elf
+#elsif
+#elseif
+#elfidef
+#elfindef
+#elfinndef
+#els
+#endi
+#endif
+
+#ifdef UNDEFINED
+# in in order to perform
+#endif
+
+#ifdef UNDEFINED
+#i
+#endif
+
+#if special_compiler
+#special_compiler_directive
+#endif