Add opt-in unneeded_throws_rethrows rule
#6069
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Source/SwiftLintBuiltInRules/Rules/Lint/UnneededThrowsRule.swift
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msrutek-paylocity
approved these changes
May 6, 2025
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@SimplyDanny Any thoughts on this? :) |
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@tonyskansf It seems that some conflicts have arisen, would you mind resolving them? Thanks! |
SimplyDanny
requested changes
Jun 30, 2025
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Looks very good already! You thought about many special cases already. The rule also makes sense. But adding it as opt-in is important as it can cause false positives in the context of protocol implementations (and maybe more occasions).
I've added a few comments. Please also check the findings reported by the OSS scan.
| @@ -12,7 +12,9 @@ | |||
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| ### Enhancements | |||
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| * None. | |||
| * Add opt-in `unneeded_throws_rethrows` rules that triggers when declarations | |||
| marked `throws`/`rethrows` never actually throw or call any throwing code. | |||
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Please append two spaces to the end of the description. They are required to enforce a line break in the rendered Markdown.
| static let description = RuleDescription( | ||
| identifier: "unneeded_throws_rethrows", | ||
| name: "Unneeded (re)throws keyword", | ||
| description: "Non-throwing functions/variables should not be marked as `throws` or `rethrows`", |
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Suggested change
| description: "Non-throwing functions/variables should not be marked as `throws` or `rethrows`", | |
| description: "Non-throwing functions/properties/closures should not be marked as `throws` or `rethrows`.", |
| violations.append( | ||
| ReasonedRuleViolation( | ||
| position: throwsToken.positionAfterSkippingLeadingTrivia, | ||
| reason: reason, |
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Suggested change
| reason: reason, | |
| reason: "Superfluous 'throws'; " + reason, |
| if let closedScope = scopes.closeScope() { | ||
| validateScope( | ||
| closedScope, | ||
| reason: "The closure type does not throw any error" |
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To keep it short:
Suggested change
| reason: "The closure type does not throw any error" | |
| reason: "closure type does not throw any error" |
| final class Visitor: ViolationsSyntaxVisitor<ConfigurationType> { | ||
| private var scopes = Stack<Scope>() | ||
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| override func visit(_: ProtocolDeclSyntax) -> SyntaxVisitorContinueKind { |
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As a shortcut, you can use skippableDeclarations to ignore declarations you don't need to consider.
| catch is SomeError {} | ||
| catch {} | ||
| } | ||
| """), |
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There should also be an example (especially a correction) making use of "typed throws".
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| children(viewMode: .sourceAccurate).contains { child in | ||
| child.is(InitializerClauseSyntax.self) | ||
| } |
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Suggested change
| children(viewMode: .sourceAccurate).contains { child in | |
| child.is(InitializerClauseSyntax.self) | |
| } | |
| initializer != nil |
Is that not possible?
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| var children = Set(typeAnnotation.children(viewMode: .sourceAccurate)) | ||
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| while let child = children.popFirst() { |
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That's dangerous. Consider this example:
let s: S<() throws -> Void> = S()I think, you should be explicit about the syntax structure to match instead of iterating through all children.
| reason: reason, | ||
| correction: ReasonedRuleViolation.ViolationCorrection( | ||
| start: throwsToken.positionAfterSkippingLeadingTrivia, | ||
| end: throwsToken.endPosition, |
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You need to use endPositionBeforeTrailingTrivia here to avoid removing trailing trivia.
| } | ||
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| override func visitPost(_ node: FunctionCallExprSyntax) { | ||
| if node.containsTaskDeclaration { |
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I don't understand this exclusion of tasks to be honest. Could you explain?
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You need to rebase onto |
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Add a new opt-in rule that detects unnecessary
throws, helping avoid misleading definitions and requirements for the caller to write unnecessary error handling.