Fix indentation_width false positives for multi-line conditions

Skip continuation lines of multi-line `guard`/`if`/`while` condition
lists that are aligned to the keyword rather than following the
`indentation_width` grid. Add `include_multiline_conditions` option
(default: `false`) to control this behavior.

Fixes #4961

Author: Pavlo Tanaiev

CHANGELOG.md

@@ -31,6 +31,13 @@
   [SimplyDanny](https://github.com/SimplyDanny)
   [#6466](https://github.com/realm/SwiftLint/issues/6466)
 
+* Fix false positives in `indentation_width` rule for continuation lines
+  of multi-line `guard`/`if`/`while` conditions. A new option
+  `include_multiline_conditions` (default: `false`) controls whether
+  these lines are checked for indentation.
+  [tanaev](https://github.com/tanaev)
+  [#4961](https://github.com/realm/SwiftLint/issues/4961)
+
 ## 0.63.2: High-Speed Extraction
 
 ### Breaking

Source/SwiftLintBuiltInRules/Rules/RuleConfigurations/IndentationWidthConfiguration.swift

@@ -22,4 +22,6 @@ struct IndentationWidthConfiguration: SeverityBasedRuleConfiguration {
     private(set) var includeCompilerDirectives = true
     @ConfigurationElement(key: "include_multiline_strings")
     private(set) var includeMultilineStrings = true
+    @ConfigurationElement(key: "include_multiline_conditions")
+    private(set) var includeMultilineConditions = false
 }

Source/SwiftLintBuiltInRules/Rules/Style/IndentationWidthRule.swift

@@ -1,5 +1,6 @@
 import Foundation
 import SourceKittenFramework
+import SwiftSyntax
 
 @DisabledWithoutSourceKit
 struct IndentationWidthRule: OptInRule {
@@ -31,6 +32,18 @@ struct IndentationWidthRule: OptInRule {
             Example("firstLine\n\tsecondLine\n\t\tthirdLine\n\n\t\tfourthLine"),
             Example("firstLine\n\tsecondLine\n\t\tthirdLine\n\t//test\n\t\tfourthLine"),
             Example("firstLine\n    secondLine\n        thirdLine\nfourthLine"),
+            Example("""
+                guard let x = foo(),
+                      let y = bar() else {
+                    return
+                }
+                """),
+            Example("""
+                if let x = foo(),
+                   let y = bar() {
+                    doSomething()
+                }
+                """),
         ],
         triggeringExamples: [
             Example("↓    firstLine", testMultiByteOffsets: false, testDisableCommand: false),
@@ -46,6 +59,14 @@ struct IndentationWidthRule: OptInRule {
         var violations: [StyleViolation] = []
         var previousLineIndentations: [Indentation] = []
 
+        let multilineConditionLines: Set<Int>
+        if !configuration.includeMultilineConditions {
+            let visitor = MultilineConditionLineVisitor(locationConverter: file.locationConverter)
+            multilineConditionLines = visitor.walk(tree: file.syntaxTree, handler: \.continuationLines)
+        } else {
+            multilineConditionLines = []
+        }
+
         for line in file.lines {
             if ignoreCompilerDirective(line: line, in: file) { continue }
 
@@ -55,6 +76,8 @@ struct IndentationWidthRule: OptInRule {
 
             if ignoreComment(line: line, in: file) || ignoreMultilineStrings(line: line, in: file) { continue }
 
+            if multilineConditionLines.contains(line.index) { continue }
+
             // Get space and tab count in prefix
             let prefix = String(line.content.prefix(indentationCharacterCount))
             let tabCount = prefix.filter { $0 == "\t" }.count
@@ -203,3 +226,32 @@ struct IndentationWidthRule: OptInRule {
         )
     }
 }
+
+private final class MultilineConditionLineVisitor: SyntaxVisitor {
+    private let locationConverter: SourceLocationConverter
+    private(set) var continuationLines = Set<Int>()
+
+    init(locationConverter: SourceLocationConverter) {
+        self.locationConverter = locationConverter
+        super.init(viewMode: .sourceAccurate)
+    }
+
+    override func visitPost(_ node: GuardStmtSyntax) {
+        collectContinuationLines(keyword: node.guardKeyword, conditions: node.conditions)
+    }
+
+    override func visitPost(_ node: IfExprSyntax) {
+        collectContinuationLines(keyword: node.ifKeyword, conditions: node.conditions)
+    }
+
+    override func visitPost(_ node: WhileStmtSyntax) {
+        collectContinuationLines(keyword: node.whileKeyword, conditions: node.conditions)
+    }
+
+    private func collectContinuationLines(keyword: TokenSyntax, conditions: ConditionElementListSyntax) {
+        let keywordLine = locationConverter.location(for: keyword.positionAfterSkippingLeadingTrivia).line
+        let conditionsEndLine = locationConverter.location(for: conditions.endPositionBeforeTrailingTrivia).line
+        guard keywordLine < conditionsEndLine else { return }
+        continuationLines.formUnion((keywordLine + 1)...conditionsEndLine)
+    }
+}

Tests/BuiltInRulesTests/IndentationWidthRuleTests.swift

@@ -268,13 +268,81 @@ final class IndentationWidthRuleTests: SwiftLintTestCase {
         assert1Violation(in: example4, includeMultilineStrings: true)
     }
 
+    func testIncludeMultilineConditions() {
+        // Multi-line guard — no violation with default config (includeMultilineConditions: false)
+        assertNoViolation(in: """
+            guard let x = foo(),
+                  let y = bar() else {
+                return
+            }
+            """)
+
+        // Multi-line if — no violation
+        assertNoViolation(in: """
+            if let x = foo(),
+               let y = bar() {
+                doSomething()
+            }
+            """)
+
+        // Multi-line while — no violation
+        assertNoViolation(in: """
+            while let x = foo(),
+                  let y = bar() {
+                doSomething()
+            }
+            """)
+
+        // Multi-line guard with includeMultilineConditions: true — violations fire
+        assert1Violation(in: """
+            guard let x = foo(),
+                  let y = bar() else {
+                return
+            }
+            """, includeMultilineConditions: true)
+
+        // Multi-line if with includeMultilineConditions: true — violations fire
+        assert1Violation(in: """
+            if let x = foo(),
+               let y = bar() {
+                doSomething()
+            }
+            """, includeMultilineConditions: true)
+
+        // Single-line guard still works normally
+        assertNoViolation(in: """
+            guard let x = foo() else {
+                return
+            }
+            """)
+
+        // Conditions on separate lines with proper indentation — no violation either way
+        assertNoViolation(in: """
+            guard
+                let x = foo(),
+                let y = bar()
+            else {
+                return
+            }
+            """)
+        assertNoViolation(in: """
+            guard
+                let x = foo(),
+                let y = bar()
+            else {
+                return
+            }
+            """, includeMultilineConditions: true)
+    }
+
     // MARK: Helpers
     private func countViolations(
         in example: Example,
         indentationWidth: Int? = nil,
         includeComments: Bool = true,
         includeCompilerDirectives: Bool = true,
         includeMultilineStrings: Bool = true,
+        includeMultilineConditions: Bool = false,
         file: StaticString = #filePath,
         line: UInt = #line
     ) -> Int {
@@ -285,6 +353,7 @@ final class IndentationWidthRuleTests: SwiftLintTestCase {
         configDict["include_comments"] = includeComments
         configDict["include_compiler_directives"] = includeCompilerDirectives
         configDict["include_multiline_strings"] = includeMultilineStrings
+        configDict["include_multiline_conditions"] = includeMultilineConditions
 
         guard let config = makeConfig(configDict, IndentationWidthRule.identifier) else {
             XCTFail("Unable to create rule configuration.", file: (file), line: line)
@@ -301,6 +370,7 @@ final class IndentationWidthRuleTests: SwiftLintTestCase {
         includeComments: Bool = true,
         includeCompilerDirectives: Bool = true,
         includeMultilineStrings: Bool = true,
+        includeMultilineConditions: Bool = false,
         file: StaticString = #filePath,
         line: UInt = #line
     ) {
@@ -311,6 +381,7 @@ final class IndentationWidthRuleTests: SwiftLintTestCase {
                 includeComments: includeComments,
                 includeCompilerDirectives: includeCompilerDirectives,
                 includeMultilineStrings: includeMultilineStrings,
+                includeMultilineConditions: includeMultilineConditions,
                 file: file,
                 line: line
             ),
@@ -326,6 +397,7 @@ final class IndentationWidthRuleTests: SwiftLintTestCase {
         includeComments: Bool = true,
         includeCompilerDirectives: Bool = true,
         includeMultilineStrings: Bool = true,
+        includeMultilineConditions: Bool = false,
         file: StaticString = #filePath,
         line: UInt = #line
     ) {
@@ -336,6 +408,7 @@ final class IndentationWidthRuleTests: SwiftLintTestCase {
             includeComments: includeComments,
             includeCompilerDirectives: includeCompilerDirectives,
             includeMultilineStrings: includeMultilineStrings,
+            includeMultilineConditions: includeMultilineConditions,
             file: file,
             line: line
         )
@@ -347,6 +420,7 @@ final class IndentationWidthRuleTests: SwiftLintTestCase {
         includeComments: Bool = true,
         includeCompilerDirectives: Bool = true,
         includeMultilineStrings: Bool = true,
+        includeMultilineConditions: Bool = false,
         file: StaticString = #filePath,
         line: UInt = #line
     ) {
@@ -357,6 +431,7 @@ final class IndentationWidthRuleTests: SwiftLintTestCase {
             includeComments: includeComments,
             includeCompilerDirectives: includeCompilerDirectives,
             includeMultilineStrings: includeMultilineStrings,
+            includeMultilineConditions: includeMultilineConditions,
             file: file,
             line: line
         )

Tests/IntegrationTests/Resources/default_rule_configurations.yml

@@ -538,6 +538,7 @@ indentation_width:
   include_comments: true
   include_compiler_directives: true
   include_multiline_strings: true
+  include_multiline_conditions: false
   meta:
     opt-in: true
     correctable: false