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Flag unused variables in multiple assignments in UseDeclaredVarsMoreThanAssignments - #2227
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Ethan Aldrich (0x000NULL) wants to merge 2 commits into
Open
Ethan Aldrich (0x000NULL) wants to merge 2 commits into
Ethan Aldrich (0x000NULL) wants to merge 2 commits into
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UseDeclaredVarsMoreThanAssignments only looked at assignments whose left-hand side is a single variable, so `$a, $b = $null` was never flagged. Treat each variable of an array literal on the left-hand side like a single-variable assignment, and stop at the first matching variable when checking whether a reference is the assignment itself. Fix PowerShell#2164
Ethan Aldrich (0x000NULL)
requested review from
a team and
Christoph Bergmeister (bergmeister)
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October 19, 2026 14:49
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🟡 Changes recommended
Reference classification still mistakes repeated writes for uses and index reads for writes, producing missed and incorrect warnings.
2 open issues
What changed in this PR
Extends PSUseDeclaredVarsMoreThanAssignments to detect unused variables in multiple assignments, addressing #2164.
Changes:
- Tracks individual variables on multiple-assignment left-hand sides.
- Stops reference matching at the first match.
- Adds three regression tests for unused and used variables.
| File | Description |
|---|---|
| Tests/Rules/UseDeclaredVarsMoreThanAssignments.tests.ps1 | Tests multiple-assignment diagnostics. |
| Rules/UseDeclaredVarsMoreThanAssignments.cs | Adds array-target tracking and first-match handling. |
Review effort: Balanced
Comment on lines
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| if (!assignmentsDictionary_OrdinalIgnoreCase.ContainsKey(variableName)) | ||
| { | ||
| assignmentsDictionary_OrdinalIgnoreCase.Add(variableName, assignmentAst); |
Comment on lines
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| // A multiple assignment has several variables on the lhs, so stop at the first match | ||
| if (inAssignment) | ||
| { | ||
| break; |
Author
|
@microsoft-github-policy-service agree |
Reassigning a variable from a multiple assignment, as in `$a, $b = 1, 2; $a = 3`, was counted as a use, unlike `$a = 1; $a = 3`. Variables read inside another target, as in `$i, $x[$i] = 0, 42`, were counted as writes, so `$i` was wrongly flagged.
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PR Summary
PSUseDeclaredVarsMoreThanAssignmentsnow flags unused variables in a multiple assignment such as$a, $b = $null. Before, it only flagged assignments whose left-hand side was a single variable.[int]$a, $b = 1, 2are covered by the existingConvertExpressionAsthandling.$a, $b) as its extent, the same as the existing code. The suppression ID is the variable name, so suppressing by name still works.Fixes #2164
How tested:
Tests/Rules/UseDeclaredVarsMoreThanAssignments.tests.ps1:UseDeclaredVarsMoreThanAssignments.tests.ps1passes 32/32 and all ofTests/Rulespasses 1742, with 0 failed and 7 skipped (PowerShell 7.6.7, Windows 11).This only touches
AnalyzeScriptBlockAst, so it doesn't conflict with the expression-bodied member changes in #2182.PR Checklist
.cs,.ps1and.psm1files have the correct copyright header (no new files)