[clang] [clang-format] Detect language for file templates (PR #191502)

[via cfe-commits]

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@@ -4427,7 +4427,13 @@ const char *StyleOptionHelpDescription =
     "4. \"{key: value, ...}\" to set specific parameters, e.g.:\n"
     "   --style=\"{BasedOnStyle: llvm, IndentWidth: 8}\"";
 
-static FormatStyle::LanguageKind getLanguageByFileName(StringRef FileName) {
+static FormatStyle::LanguageKind getLanguageByFileName(StringRef &FileName) {
+  constexpr std::array TemplateSuffixes{StringRef{".in"},
+                                        StringRef{".template"}};
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owenca wrote:

Not dropping, but replacing with `llvm::StringLiteral` to be consistent with line 3321:
```c++
    static constexpr llvm::StringLiteral FoundationIdentifiers[] = {
```

https://github.com/llvm/llvm-project/pull/191502