[clang] [clang][NFC] add comments for canBeJoined function (PR #150766)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Jongmyeong Choi (jongmyeong-choi)

<details>
<summary>Changes</summary>

- Convert simple comment to detailed Doxygen-style documentation
- Add comprehensive examples of token concatenation cases
- Include examples of safe adjacency cases
- Clarify the function's purpose and return value semantics

---
Full diff: https://github.com/llvm/llvm-project/pull/150766.diff


1 Files Affected:

- (modified) clang/lib/Edit/EditedSource.cpp (+17-1) 


``````````diff
diff --git a/clang/lib/Edit/EditedSource.cpp b/clang/lib/Edit/EditedSource.cpp
index 398cce71d5e27..04b0f794055b3 100644
--- a/clang/lib/Edit/EditedSource.cpp
+++ b/clang/lib/Edit/EditedSource.cpp
@@ -308,7 +308,23 @@ bool EditedSource::commit(const Commit &commit) {
   return true;
 }
 
-// Returns true if it is ok to make the two given characters adjacent.
+/// Checks if two characters can be placed adjacent without creating unintended tokens.
+///
+/// Returns false when adjacency would cause token concatenation:
+///   - 'a' + 'b' → "ab" (different identifier)  
+///   - '<' + '<' → "<<" (shift operator)
+///   - '+' + '+' → "++" (increment operator)
+///   - '/' + '*' → "/*" (comment start)
+///
+/// Returns true when adjacency is safe:
+///   - 'a' + ')' → "a)" (separate tokens)
+///   - '5' + ')' → "5)" (separate tokens)
+///
+/// Used by adjustRemoval() to decide whether to insert space during text removal.
+///
+/// @param left Character on the left side
+/// @param right Character on the right side
+/// @return true if safe to place adjacent, false if space needed
 static bool canBeJoined(char left, char right, const LangOptions &LangOpts) {
   // FIXME: Should use TokenConcatenation to make sure we don't allow stuff like
   // making two '<' adjacent.

``````````

</details>


https://github.com/llvm/llvm-project/pull/150766