Add SwiftLint rule to prevent multiple variable declarations on one line

CHANGELOG.md

@@ -20,6 +20,8 @@
 * Add new `opaque_over_existential` opt-in rule that triggers when the existential `any` type of a
   function parameter can be replaced with an opaque `some` type.  
   [SimplyDanny](https://github.com/SimplyDanny)
+* Add new `multiple_variable_declaration` opt-in rule that triggers when the there's any declaration of variable and/or constants at the same line.  
+  [Ahmad Zaghloul](https://github.com/AhmedZaghloul19)
 
 ### Bug Fixes
 

Source/SwiftLintBuiltInRules/Models/BuiltInRules.swift

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

Source/SwiftLintBuiltInRules/Rules/Style/MultipleVariableDeclarationRule.swift

@@ -0,0 +1,60 @@
+import SwiftSyntax
+
+@SwiftSyntaxRule(optIn: true)
+struct MultipleVariableDeclarationRule: Rule {
+    var configuration = SeverityConfiguration<Self>(.warning)
+
+    static let description = RuleDescription(
+        identifier: "multiple_variable_declaration",
+        name: "Multiple Variable Declaration",
+        description: "Variables should not be declared on the same line",
+        kind: .style,
+        nonTriggeringExamples: [
+            Example(
+                """
+                    let a = 1
+                    let b = 2
+                """
+                ),
+            Example(
+                """
+                    var x = 10
+                    var y = 20
+                """
+            ),
+            Example(
+                """
+                    let x = 10
+                    var y = 20
+                """
+            ),
+        ],
+        triggeringExamples: [
+            Example("let a = 1; let b = 2"),
+            Example("var x = 10; var y = 20"),
+            Example("let x = 10; var y = 20"),
+        ]
+    )
+}
+
+private extension MultipleVariableDeclarationRule {
+    final class Visitor: ViolationsSyntaxVisitor<ConfigurationType> {
+        private var lastVariableLine: Int?
+
+        override func visit(_ node: VariableDeclSyntax) -> SyntaxVisitorContinueKind {
+            let converter = file.locationConverter
+            let currentLocation = converter
+                .location(for: node.positionAfterSkippingLeadingTrivia)
+            let currentLine = currentLocation.line
+            guard currentLine > 0 else {
+                return .skipChildren
+            }
+
+            if let lastLine = lastVariableLine, lastLine == currentLine {
+                violations.append(node.positionAfterSkippingLeadingTrivia)
+            }
+            lastVariableLine = currentLine
+            return .visitChildren
+        }
+    }
+}

Tests/GeneratedTests/GeneratedTests.swift

@@ -715,6 +715,12 @@ final class MultipleClosuresWithTrailingClosureRuleGeneratedTests: SwiftLintTest
     }
 }
 
+final class MultipleVariableDeclarationRuleGeneratedTests: SwiftLintTestCase {
+    func testWithDefaultConfiguration() {
+        verifyRule(MultipleVariableDeclarationRule.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_variable_declaration:
+  severity: warning
+  meta:
+    opt-in: true
 nesting:
   type_level:
     warning: 1