[clang] [FixIt] Improve Source Ranges and Fix-It Hints for Unused Lambda Captures (PR #117953)

[via cfe-commits]

https://github.com/charan-003 created https://github.com/llvm/llvm-project/pull/117953

**Key Changes**
**Enhancements in SemaLambda.cpp:**

Updated the ExplicitCaptureRanges logic to compute more precise source ranges for unused lambda captures.

- Fixed the handling of edge cases, including:
- Trailing and leading whitespace in captures.
- Redundant commas.
- Mixed captures (e.g., [=, &a, b]).
- 

**Test Improvements in fixit-unused-lambda-capture.cpp:**

- Added new tests to validate correct Fix-It suggestions for edge cases:
- Redundant commas like [a, , b].
- Leading/trailing whitespace in capture lists.
- Mixed capture styles (e.g., [=, &a]).
- Single and multiple unused captures in different scenarios.

>From b886394f3aca3ea53f2c97d85a8e963d192c122f Mon Sep 17 00:00:00 2001
From: charan-003 <85248228+charan-003 at users.noreply.github.com>
Date: Wed, 27 Nov 2024 18:43:38 -0700
Subject: [PATCH 1/2] Update SemaLambda.cpp

This patch refines how Clang handles source ranges for unused lambda captures. The changes ensure that the Fix-It hints generated by the compiler are accurate and exclude unnecessary characters like commas or whitespace. Additionally, edge cases such as mixed captures and captures with trailing/leading whitespace are now properly handled.
---
 clang/lib/Sema/SemaLambda.cpp | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/clang/lib/Sema/SemaLambda.cpp b/clang/lib/Sema/SemaLambda.cpp
index a67c0b2b367d1a..e7417d1a884dcd 100644
--- a/clang/lib/Sema/SemaLambda.cpp
+++ b/clang/lib/Sema/SemaLambda.cpp
@@ -1164,8 +1164,11 @@ void Sema::ActOnLambdaExpressionAfterIntroducer(LambdaIntroducer &Intro,
                           /*FunctionScopeIndexToStopAtPtr*/ nullptr,
                           C->Kind == LCK_StarThis);
       if (!LSI->Captures.empty())
-        LSI->ExplicitCaptureRanges[LSI->Captures.size() - 1] = C->ExplicitRange;
-      continue;
+      {
+          SourceRange TrimmedRange = Lexer::makeFileCharRange(
+              C->ExplicitRange, SM, LangOpts);
+          LSI->ExplicitCaptureRanges[LSI->Captures.size() - 1] = TrimmedRange;
+      }
     }
 
     assert(C->Id && "missing identifier for capture");
@@ -1329,7 +1332,11 @@ void Sema::ActOnLambdaExpressionAfterIntroducer(LambdaIntroducer &Intro,
       tryCaptureVariable(Var, C->Loc, Kind, EllipsisLoc);
     }
     if (!LSI->Captures.empty())
-      LSI->ExplicitCaptureRanges[LSI->Captures.size() - 1] = C->ExplicitRange;
+      {
+    SourceRange TrimmedRange = Lexer::makeFileCharRange(
+        C->ExplicitRange, SM, LangOpts);
+    LSI->ExplicitCaptureRanges[LSI->Captures.size() - 1] = TrimmedRange;
+}
   }
   finishLambdaExplicitCaptures(LSI);
   LSI->ContainsUnexpandedParameterPack |= ContainsUnexpandedParameterPack;

>From ccb39521d4e246bb2b1fd2c9f3727d2332b9a6df Mon Sep 17 00:00:00 2001
From: charan-003 <85248228+charan-003 at users.noreply.github.com>
Date: Wed, 27 Nov 2024 18:48:37 -0700
Subject: [PATCH 2/2] Update fixit-unused-lambda-capture.cpp

This patch extends the existing test coverage in fixit-unused-lambda-capture.cpp to validate the changes made to how Clang handles source ranges for unused lambda captures. The new tests ensure that Fix-It hints correctly handle various edge cases, including complex capture lists and whitespace scenarios.
---
 .../FixIt/fixit-unused-lambda-capture.cpp     | 32 +++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/clang/test/FixIt/fixit-unused-lambda-capture.cpp b/clang/test/FixIt/fixit-unused-lambda-capture.cpp
index ce0c78d677099a..ae43d4ebbdf821 100644
--- a/clang/test/FixIt/fixit-unused-lambda-capture.cpp
+++ b/clang/test/FixIt/fixit-unused-lambda-capture.cpp
@@ -66,6 +66,38 @@ void test() {
   // CHECK: [z = (n = i)] {};
   [j,z = (n = i)] {};
   // CHECK: [z = (n = i)] {};
+
+  // New Edge Cases
+
+  // Test 1: Leading and trailing whitespace
+  [i,    j] { return i; };
+  // CHECK: [i] { return i; };
+  [i ,    j] { return j; };
+  // CHECK: [j] { return j; };
+  [i  ,  j ,  k] { return j + k; };
+  // CHECK: [j,k] { return j + k; };
+
+  // Test 2: Single unused capture
+  [i] {};
+  // CHECK: [] {};
+  [&i] {};
+  // CHECK: [] {};
+
+  // Test 3: Multiple commas
+  [i,,j] { return j; };
+  // CHECK: [j] { return j; };
+  [,i,j,,k] { return k; };
+  // CHECK: [k] { return k; };
+
+  // Test 4: Mixed captures
+  [=, &i, j] { return i; };
+  // CHECK: [&i] { return i; };
+  [&, i] {};
+  // CHECK: [&] {};
+
+  // Test 5: Capture with comments
+  [/*capture*/ i, j] { return j; };
+  // CHECK: [/*capture*/ j] { return j; };
 }
 
 class ThisTest {