[clang-format] Hanlde leading whitespaces for JSON files

[owenpan]

Summary

Fixes https://github.com/llvm/llvm-project/issues/62228 and https://github.com/llvm/llvm-project/issues/62229.

[rymiel]

(looks like you linked the same issue twice in the summary)

[owenpan]

In D148777#4282574, @rymiel wrote:

(looks like you linked the same issue twice in the summary)

Thanks. Fixed.

[MyDeveloperDay]

LGTM

clang/lib/Format/Format.cpp

if (Style.isJson()) {
     auto Env = Environment::make(Code, FileName, Ranges, FirstStartColumn,
                                  NextStartColumn, LastStartColumn);
     if (!Env)
       return {};
     // Perform the actual formatting pass.
     tooling::Replacements Replaces =
         Formatter(*Env, Style, Status).process().first;
     // add a replacement to remove the "x = " from the result.
-    if (!Replaces.add(tooling::Replacement(FileName, 0, 4, ""))) {
-      // apply the reformatting changes and the removal of "x = ".
-      if (applyAllReplacements(Code, Replaces))
-        return {Replaces, 0};
-    }
+    Replaces = Replaces.merge(
+        tooling::Replacements(tooling::Replacement(FileName, 0, 4, "")));
     return {tooling::Replacements(), 0};
   }
 
   auto Env = Environment::make(Code, FileName, Ranges, FirstStartColumn,
                                NextStartColumn, LastStartColumn);
   if (!Env)
     return {};
 

clang/unittests/Format/FormatTestJson.cpp

TEST_F(FormatTestJson, SpaceBeforeJsonColon) {
   Style.SpaceBeforeJsonColon = true;
   verifyFormatStable("{}", Style);
   verifyFormatStable("{\n"
                      "  \"name\" : 1\n"
                      "}",
                      Style);
 }
 
+TEST_F(FormatTestJson, StartsWithWhitespaces) {
+  FormatStyle Style = getLLVMStyle(FormatStyle::LK_Json);
+  EXPECT_EQ("{\n"
+            "  \"name\": 1\n"
+            "}",
+            format(" {\n"
+                   "  \"name\": 1\n"
+                   "}",
+                   Style));
+
+  // FIXME: The block below is over-indented.
+  EXPECT_EQ("    {\n"
+            "      \"name\": 1\n"
+            "    }",
+            format("\n{\n"
+                   "  \"name\": 1\n"
+                   "}",
+                   Style));
+}
+
 } // namespace format
 } // end namespace clang