Ignore locally defined count identifiers in empty_count rule (#6202)

Author: SimplyDanny

BUILD

@@ -123,6 +123,7 @@ swift_library(
     visibility = ["//visibility:public"],
     deps = [
         ":SwiftLintCore",
+        "@SwiftSyntax//:SwiftLexicalLookup_opt",
     ],
 )
 

CHANGELOG.md

@@ -39,6 +39,10 @@
   improvements done in the [SwiftSyntax](https://github.com/swiftlang/swift-syntax)
   library.
 
+* Ignore locally defined `count` identifiers in `empty_count` rule.  
+  [SimplyDanny](https://github.com/SimplyDanny)
+  [#5326](https://github.com/realm/SwiftLint/issues/5326)
+
 * The `private_swiftui_state` rule now applies to `ViewModifier` types.  
   [mt00chikin](https://github.com/mt00chikin)
 

Package.swift

@@ -107,7 +107,10 @@ let package = Package(
         ),
         .target(
             name: "SwiftLintBuiltInRules",
-            dependencies: ["SwiftLintCore"],
+            dependencies: [
+                .product(name: "SwiftLexicalLookup", package: "swift-syntax"),
+                "SwiftLintCore",
+            ],
             swiftSettings: swiftFeatures + strictConcurrency
         ),
         .target(

Source/SwiftLintBuiltInRules/Rules/Performance/EmptyCountRule.swift

@@ -1,3 +1,5 @@
+@_spi(Experimental)
+import SwiftLexicalLookup
 import SwiftLintCore
 import SwiftSyntax
 
@@ -22,6 +24,14 @@ struct EmptyCountRule: Rule {
             Example("order.discount == 0"),
             Example("let rule = #Rule(Tips.Event(id: \"someTips\")) { $0.donations.count == 0 }"),
             Example("#Rule(param1: \"param1\")", excludeFromDocumentation: true),
+            Example("func isEmpty(count: Int) -> Bool { count == 0 }"),
+            Example("""
+                var isEmpty: Bool {
+                    let count = 0
+                    return count == 0
+                }
+                """),
+            Example("{ count in count == 0 }()"),
         ],
         triggeringExamples: [
             Example("[Int]().↓count == 0"),
@@ -50,7 +60,18 @@ struct EmptyCountRule: Rule {
                     doSomething()
                     return $0.donations.↓count == 0
                 }
-            """, excludeFromDocumentation: true),
+                """, excludeFromDocumentation: true),
+            Example("""
+                extension E {
+                    var isEmpty: Bool { ↓count == 0 }
+                }
+                """, excludeFromDocumentation: true),
+            Example(
+                """
+                struct S {
+                    var isEmpty: Bool { ↓count == 0 }
+                }
+                """, excludeFromDocumentation: true),
         ],
         corrections: [
             Example("[].↓count == 0"):
@@ -146,19 +167,31 @@ private extension EmptyCountRule {
 }
 
 private extension ExprSyntax {
+    var isNonLocalCountIdentifier: Bool {
+        guard let declRef = self.as(DeclReferenceExprSyntax.self),
+              declRef.argumentNames == nil,
+              declRef.baseName.tokenKind == .identifier("count") else {
+            return false
+        }
+        let result = lookup(Identifier(canonicalName: "count"))
+        return result.isEmpty || !result.contains { result in
+            switch result {
+            case .fromScope: true
+            default: false
+            }
+        }
+    }
+
     func countCallPosition(onlyAfterDot: Bool) -> AbsolutePosition? {
         if let expr = self.as(MemberAccessExprSyntax.self) {
             if expr.declName.argumentNames == nil, expr.declName.baseName.tokenKind == .identifier("count") {
                 return expr.declName.baseName.positionAfterSkippingLeadingTrivia
             }
-
             return nil
         }
-
-        if !onlyAfterDot, let expr = self.as(DeclReferenceExprSyntax.self) {
-            return expr.baseName.tokenKind == .identifier("count") ? expr.positionAfterSkippingLeadingTrivia : nil
+        if !onlyAfterDot, isNonLocalCountIdentifier {
+            return positionAfterSkippingLeadingTrivia
         }
-
         return nil
     }
 }