[clang-format] Remove spurious JSON binding when DisableFormat = true

Relevant issue: #52705

When the `DisableFormat` option of `clang-format` is set to `true` and a JSON file is formatted, the ephemeral variable binding that is added to the top-level object is not removed from the formatted file.  For example, this JSON:
```
{
  "key": "value"
}
```
Is reformatted to:
```
x = {
  "key": "value"
}
```
Which is not valid JSON syntax.  This fix avoids the addition of this binding when `DisableFormat` is set to `true`, ensuring that it cannot be left behind when formatting is disabled.

Reviewed By: MyDeveloperDay, HazardyKnusperkeks

Differential Revision: https://reviews.llvm.org/D115769

Fixes #52705

clang/tools/clang-format/ClangFormat.cpp

@@ -460,7 +460,7 @@ static bool format(StringRef FileName) {
 
   // To format JSON insert a variable to trick the code into thinking its
   // JavaScript.
-  if (FormatStyle->isJson()) {
+  if (FormatStyle->isJson() && !FormatStyle->DisableFormat) {
     auto Err = Replaces.add(tooling::Replacement(
         tooling::Replacement(AssumedFileName, 0, 0, "x = ")));
     if (Err) {

clang/unittests/Format/FormatTestJson.cpp

@@ -27,7 +27,7 @@ class FormatTestJson : public ::testing::Test {
 
     // Mock up what ClangFormat.cpp will do for JSON by adding a variable
     // to trick JSON into being JavaScript
-    if (Style.isJson()) {
+    if (Style.isJson() && !Style.DisableFormat) {
       auto Err = Replaces.add(
           tooling::Replacement(tooling::Replacement("", 0, 0, "x = ")));
       if (Err) {
@@ -60,10 +60,15 @@ class FormatTestJson : public ::testing::Test {
     return Style;
   }
 
+  static void verifyFormatStable(llvm::StringRef Code,
+                                 const FormatStyle &Style) {
+    EXPECT_EQ(Code.str(), format(Code, Style)) << "Expected code is not stable";
+  }
+
   static void
   verifyFormat(llvm::StringRef Code,
                const FormatStyle &Style = getLLVMStyle(FormatStyle::LK_Json)) {
-    EXPECT_EQ(Code.str(), format(Code, Style)) << "Expected code is not stable";
+    verifyFormatStable(Code, Style);
     EXPECT_EQ(Code.str(), format(test::messUp(Code), Style));
   }
 };
@@ -193,5 +198,24 @@ TEST_F(FormatTestJson, JsonNoStringSplit) {
                Style);
 }
 
+TEST_F(FormatTestJson, DisableJsonFormat) {
+  FormatStyle Style = getLLVMStyle(FormatStyle::LK_Json);
+  verifyFormatStable("{}", Style);
+  verifyFormatStable("{\n"
+                     "  \"name\": 1\n"
+                     "}",
+                     Style);
+
+  // Since we have to disable formatting to run this test, we shall refrain from
+  // calling test::messUp lest we change the unformatted code and cannot format
+  // it back to how it started.
+  Style.DisableFormat = true;
+  verifyFormatStable("{}", Style);
+  verifyFormatStable("{\n"
+                     "  \"name\": 1\n"
+                     "}",
+                     Style);
+}
+
 } // namespace format
 } // end namespace clang