Fix false positives related to multiline strings in `indentation_width` rule (#4862)

CHANGELOG.md

@@ -29,6 +29,9 @@
   [SimplyDanny](https://github.com/SimplyDanny)
   [#4860](https://github.com/realm/SwiftLint/issues/4860)
 
+* Fix false positives in `indentation_width` rule.  
+  [Sven Münnich](https://github.com/svenmuennich)
+
 ## 0.51.0: bzllint
 
 #### Breaking

Source/SwiftLintFramework/Rules/Style/IndentationWidthRule.swift

@@ -172,10 +172,21 @@ struct IndentationWidthRule: ConfigurationProviderRule, OptInRule {
         if configuration.includeMultilineStrings {
             return false
         }
-        if file.syntaxMap.tokens(inByteRange: line.byteRange).kinds == [.string] {
-            return true
+
+        // A multiline string content line is characterized by beginning with a token of kind string whose range's lower
+        // bound is smaller than that of the line itself.
+        let tokensInLine = file.syntaxMap.tokens(inByteRange: line.byteRange)
+        guard
+            let firstToken = tokensInLine.first,
+            firstToken.kind == .string,
+            firstToken.range.lowerBound < line.byteRange.lowerBound else {
+            return false
         }
-        return false
+
+        // Closing delimiters of a multiline string should follow the defined indentation. The Swift compiler requires
+        // those delimiters to be on their own line so we need to consider the number of tokens as well as the upper
+        // bounds.
+        return tokensInLine.count > 1 || line.byteRange.upperBound < firstToken.range.upperBound
     }
 
     /// Validates whether the indentation of a specific line is valid based on the indentation of the previous line.

Tests/SwiftLintFrameworkTests/IndentationWidthRuleTests.swift

@@ -196,18 +196,57 @@ class IndentationWidthRuleTests: XCTestCase {
             """, includeCompilerDirectives: true)
     }
 
-    func testIgnoredMultilineStrings() {
-        assertNoViolation(
-            in: "let x = \"\"\"\nstring1\n    string2\n  string3\n\"\"\"\n",
-            includeMultilineStrings: false
-        )
-        assert1Violation(
-            in: "let x = \"\"\"\nstring1\n    string2\n  string3\n\"\"\"\n"
-        )
-        assertViolations(
-            in: "let x = \"\"\"\nstring1\n    string2\n  string3\n string4\n\"\"\"\n",
-            equals: 2
-        )
+    func testIncludeMultilineStrings() {
+        let example0 = #"""
+            let x = """
+                string1
+                    string2
+                  string3
+                """
+            """#
+        assertNoViolation(in: example0, includeMultilineStrings: false)
+        assert1Violation(in: example0, includeMultilineStrings: true)
+
+        let example1 = #"""
+            let x = """
+                string1
+                    string2
+                  string3
+                 string4
+                """
+            """#
+        assertNoViolation(in: example1, includeMultilineStrings: false)
+        assertViolations(in: example1, equals: 2, includeMultilineStrings: true)
+
+        let example2 = ##"""
+            let x = #"""
+                string1
+               """#
+            """##
+        assert1Violation(in: example2, includeMultilineStrings: false)
+        assert1Violation(in: example2, includeMultilineStrings: true)
+
+        let example3 = """
+            let x = [
+                "key": [
+                    ["nestedKey": "string"],
+                ],
+            ]
+            """
+        assertNoViolation(in: example3, includeMultilineStrings: false)
+        assertNoViolation(in: example3, includeMultilineStrings: true)
+
+        let example4 = #"""
+            func test() -> String {
+                """
+                ▿ Type:
+                  - property: \(123) + \(456)
+                \(true)
+                """
+            }
+            """#
+        assertNoViolation(in: example4, includeMultilineStrings: false)
+        assert1Violation(in: example4, includeMultilineStrings: true)
     }
 
     // MARK: Helpers