Fix redundantClosure false positive for async let

[Copilot]

redundantClosure incorrectly flags closures in async let declarations as redundant. The closure is not redundant here — it's required to defer execution until the value is awaited.

// This closure should not be removed
async let doAsync = {
    if 1 == 1 {
        print()
    }
}()
await doAsync

Changes:

• Added a guard in RedundantClosure.swift that detects async let/var declarations by walking backward from the = sign and skips the rule
• Added test case testKeepsClosureInAsyncLet

• Fixes redundantClosure false positive for async let #2658

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.45%. Comparing base (df2c5bd) to head (443d8ed).
⚠️ Report is 4 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2659      +/-   ##
===========================================
- Coverage    95.45%   95.45%   -0.01%     
===========================================
  Files          178      178              
  Lines        27137    27209      +72     
===========================================
+ Hits         25904    25971      +67     
- Misses        1233     1238       +5     

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[calda]

@copilot, actually the issue is that this closure is not redundant because an if with no else is not a valid if expression:

// Not valid
async let doAsync =
    if 1 == 1 { // error: 'if' must have an unconditional 'else' to be used as expression
        print()
    }

// Valid
async let doAsync =
    if 1 == 1 {
        print(1)
    } else {
        print(2)
    }

Ensure redundantClosure doesn't try to remove closures that only contain a single if branch

[Copilot]

@copilot, actually the issue is that this closure is not redundant because an if with no else is not a valid if expression:

...

Updated the fix to check for non-exhaustive if expressions instead of specifically checking for async let. The rule now verifies that the conditional statement inside the closure is exhaustive (has an unconditional else for if statements) before removing the closure. Added tests for if without else, if/else if without else, and confirmed exhaustive if/else closures are still removed correctly. See commit 0f50f47.

[calda]

@copilot this new helper / the complex code in it shouldn't be necessary, check how other if expression rules like redundantReturn or conditionalAssignment handle this.

[Copilot]

Replaced the custom indexOfConditionalKeywordInClosure helper with a direct call to conditionalBranches(at:), which already handles skipping try/await keywords. See commit 7e1f5a3.

[calda]

@copilot please lint

[Copilot]

@copilot please lint

Done in commit d89d44d.