[clang-format] Fix a bug that always returns error for JSON

Fixes #108556.

Author: owenca

clang/test/Format/dry-run-warning.cpp

@@ -0,0 +1,12 @@
+// RUN: echo '{' > %t.json
+// RUN: echo '  "married": true' >> %t.json
+// RUN: echo '}' >> %t.json
+
+// RUN: clang-format -n -style=LLVM %t.json 2>&1 | FileCheck %s -allow-empty
+// CHECK-NOT: warning
+
+// RUN: clang-format -n -style=LLVM < %t.json 2>&1 \
+// RUN:   | FileCheck %s -check-prefix=CHECK2 -strict-whitespace
+// CHECK2: warning: code should be clang-formatted
+
+// RUN: rm %t.json

clang/tools/clang-format/ClangFormat.cpp

@@ -351,9 +351,6 @@ static void outputReplacementsXML(const Replacements &Replaces) {
 static bool
 emitReplacementWarnings(const Replacements &Replaces, StringRef AssumedFileName,
                         const std::unique_ptr<llvm::MemoryBuffer> &Code) {
-  if (Replaces.empty())
-    return false;
-
   unsigned Errors = 0;
   if (WarnFormat && !NoWarnFormat) {
     SourceMgr Mgr;
@@ -490,9 +487,11 @@ static bool format(StringRef FileName, bool ErrorOnIncompleteFormat = false) {
   Replacements Replaces = sortIncludes(*FormatStyle, Code->getBuffer(), Ranges,
                                        AssumedFileName, &CursorPosition);
 
+  const bool IsJson = FormatStyle->isJson();
+
   // To format JSON insert a variable to trick the code into thinking its
   // JavaScript.
-  if (FormatStyle->isJson() && !FormatStyle->DisableFormat) {
+  if (IsJson && !FormatStyle->DisableFormat) {
     auto Err = Replaces.add(tooling::Replacement(
         tooling::Replacement(AssumedFileName, 0, 0, "x = ")));
     if (Err)
@@ -511,8 +510,10 @@ static bool format(StringRef FileName, bool ErrorOnIncompleteFormat = false) {
       reformat(*FormatStyle, *ChangedCode, Ranges, AssumedFileName, &Status);
   Replaces = Replaces.merge(FormatChanges);
   if (OutputXML || DryRun) {
-    if (DryRun)
-      return emitReplacementWarnings(Replaces, AssumedFileName, Code);
+    if (DryRun) {
+      return (Replaces.size() > IsJson ? 1 : 0) &&
+             emitReplacementWarnings(Replaces, AssumedFileName, Code);
+    }
     outputXML(Replaces, FormatChanges, Status, Cursor, CursorPosition);
   } else {
     IntrusiveRefCntPtr<llvm::vfs::InMemoryFileSystem> InMemoryFileSystem(