Add SwiftLint rule to prevent multiple variable declarations on one line

CHANGELOG.md

@@ -12,6 +12,10 @@
 
 ### Enhancements
 
+* Add `multiple_statements` opt-in rule
+  that triggers when there are multiple statements on the same line.
+  [Ahmad Zaghloul](https://github.com/AhmedZaghloul19)
+
 * Exclude types with a `@Suite` attribute and functions annotated with `@Test` from `no_magic_numbers` rule.
   Also treat a type as a `@Suite` if it contains `@Test` functions.  
   [SimplyDanny](https://github.com/SimplyDanny)

Source/SwiftLintBuiltInRules/Models/BuiltInRules.swift

@@ -121,6 +121,7 @@ public let builtInRules: [any Rule.Type] = [
     MultilineParametersBracketsRule.self,
     MultilineParametersRule.self,
     MultipleClosuresWithTrailingClosureRule.self,
+    MultipleStatementsRule.self,
     NSLocalizedStringKeyRule.self,
     NSLocalizedStringRequireBundleRule.self,
     NSNumberInitAsFunctionReferenceRule.self,

Source/SwiftLintBuiltInRules/Rules/Idiomatic/MultipleStatementsRule.swift

@@ -0,0 +1,130 @@
+import SwiftSyntax
+
+@SwiftSyntaxRule(explicitRewriter: true, optIn: true)
+struct MultipleStatementsRule: Rule {
+    var configuration = SeverityConfiguration<Self>(.warning)
+
+    static let description = RuleDescription(
+        identifier: "multiple_statements",
+        name: "Multiple Statements",
+        description: "Every statement should be on its own line",
+        kind: .idiomatic,
+        nonTriggeringExamples: [
+            Example(
+                """
+                    let a = 1;
+                    let b = 2;
+                """
+            ),
+            Example(
+                """
+                    var x = 10
+                    var y = 20;
+                """
+            ),
+            Example(
+                """
+                    let a = 1;
+                    return a
+                """
+            ),
+            Example(
+                """
+                    if b { return };  
+                    let a = 1
+                """
+            ),
+        ],
+        triggeringExamples: [
+            Example("let a = 1; return a"),
+            Example("if b { return }; let a = 1"),
+            Example("if b { return }; if c { return }"),
+            Example("let a = 1; let b = 2; let c = 0"),
+            Example("var x = 10; var y = 20"),
+            Example("let x = 10; var y = 20"),
+        ],
+        corrections: [
+            Example("let a = 0↓; let b = 0"):
+                Example(
+                    """
+                    let a = 0
+                    let b = 0
+                    """
+                ),
+            Example("let a = 0↓; let b = 0↓; let c = 0"):
+                Example(
+                    """
+                    let a = 0
+                    let b = 0
+                    let c = 0
+                    """
+                ),
+            Example("let a = 0↓; print(\"Hello\")"):
+                Example(
+                    """
+                    let a = 0
+                    print(\"Hello\")
+                    """
+                ),
+        ]
+    )
+}
+
+private extension MultipleStatementsRule {
+    final class Visitor: ViolationsSyntaxVisitor<ConfigurationType> {
+        override func visitPost(_ node: TokenSyntax) {
+            if node.isThereStatementAfterSemicolon {
+                violations.append(node.positionAfterSkippingLeadingTrivia)
+            }
+        }
+    }
+
+    final class Rewriter: ViolationsSyntaxRewriter<ConfigurationType> {
+        override func visit(_ node: TokenSyntax) -> TokenSyntax {
+            guard node.isThereStatementAfterSemicolon else {
+                return super.visit(node)
+            }
+
+            correctionPositions.append(node.positionAfterSkippingLeadingTrivia)
+            let newNode = TokenSyntax(
+                .unknown(""),
+                leadingTrivia: node.leadingTrivia,
+                trailingTrivia: .newlines(1),
+                presence: .present
+            )
+            return super.visit(newNode)
+        }
+    }
+}
+
+private extension TokenSyntax {
+    var isThereStatementAfterSemicolon: Bool {
+        guard tokenKind == .semicolon,
+            !trailingTrivia.isEmpty else { return false }
+
+        if let nextToken = nextToken(viewMode: .sourceAccurate),
+           isFollowedOnlyByWhitespaceOrNewline {
+            return nextToken.leadingTrivia.containsNewlines() == false
+        }
+        return true
+    }
+
+    var isFollowedOnlyByWhitespaceOrNewline: Bool {
+        guard let nextToken = nextToken(viewMode: .sourceAccurate),
+            !nextToken.trailingTrivia.isEmpty else {
+            return true
+        }
+        return nextToken.leadingTrivia.allSatisfy { $0.isWhitespaceOrNewline }
+    }
+}
+
+private extension TriviaPiece {
+    var isWhitespaceOrNewline: Bool {
+        switch self {
+        case .spaces, .tabs, .newlines, .carriageReturns, .carriageReturnLineFeeds:
+            return true
+        default:
+            return false
+        }
+    }
+}

Source/SwiftLintFramework/Configuration/Configuration+Remote.swift

@@ -86,7 +86,10 @@ internal extension Configuration.FileGraph.FilePath {
             // Block main thread until timeout is reached / task is done
             while true {
                 if taskDone { break }
-                if Date().timeIntervalSince(startDate) > timeout { task.cancel(); break }
+                if Date().timeIntervalSince(startDate) > timeout {
+                    task.cancel()
+                    break
+                }
                 usleep(50_000) // Sleep for 50 ms
             }
 

Tests/GeneratedTests/GeneratedTests.swift

@@ -715,6 +715,12 @@ final class MultipleClosuresWithTrailingClosureRuleGeneratedTests: SwiftLintTest
     }
 }
 
+final class MultipleStatementsRuleGeneratedTests: SwiftLintTestCase {
+    func testWithDefaultConfiguration() {
+        verifyRule(MultipleStatementsRule.description)
+    }
+}
+
 final class NSLocalizedStringKeyRuleGeneratedTests: SwiftLintTestCase {
     func testWithDefaultConfiguration() {
         verifyRule(NSLocalizedStringKeyRule.description)

Tests/IntegrationTests/default_rule_configurations.yml

@@ -564,6 +564,10 @@ multiple_closures_with_trailing_closure:
   severity: warning
   meta:
     opt-in: false
+multiple_statements_declaration:
+  severity: warning
+  meta:
+    opt-in: true
 nesting:
   type_level:
     warning: 1