From e30065e632e44cfc16125e3f0446161888ccb09b Mon Sep 17 00:00:00 2001
From: JP Simard <jp@jpsim.com>
Date: Tue, 3 Oct 2023 10:53:41 -0400
Subject: [PATCH] Prevent SwiftSyntax string interpolation errors in tests
 (#5258)

Previously this was logged to the console when running tests:

```
[ParseError] Parsing a `DeclSyntax` node from string interpolation produced the following parsing errors.
Set a breakpoint in `SyntaxParseable.logStringInterpolationParsingError()` to debug the failure.
```

And slightly improve the style of the expanded `@SwiftSyntaxRule` macro.
---
 .../SwiftLintCoreMacros/SwiftSyntaxRule.swift | 42 +++++++++----------
 Tests/MacroTests/SwiftSyntaxRuleTests.swift   | 13 ++----
 2 files changed, 24 insertions(+), 31 deletions(-)

diff --git a/Source/SwiftLintCoreMacros/SwiftSyntaxRule.swift b/Source/SwiftLintCoreMacros/SwiftSyntaxRule.swift
index 2340f7b1ad..8d307157db 100644
--- a/Source/SwiftLintCoreMacros/SwiftSyntaxRule.swift
+++ b/Source/SwiftLintCoreMacros/SwiftSyntaxRule.swift
@@ -15,33 +15,31 @@ struct SwiftSyntaxRule: ExtensionMacro {
                     func makeVisitor(file: SwiftLintFile) -> ViolationsSyntaxVisitor {
                         Visitor(viewMode: .sourceAccurate)
                     }
-                    \(createFoldingPreprocessor(from: node.foldArgument))
                 }
-                """)
-        ]
+                """),
+            try createFoldingPreprocessor(type: type, foldArgument: node.foldArgument)
+        ].compactMap { $0 }
     }
 
-    private static func createFoldingPreprocessor(from foldArgument: ExprSyntax?) -> DeclSyntax {
-        guard let foldArgument else {
-            return ""
+    private static func createFoldingPreprocessor(
+        type: some TypeSyntaxProtocol,
+        foldArgument: ExprSyntax?
+    ) throws -> ExtensionDeclSyntax? {
+        guard
+            let foldArgument,
+            let booleanLiteral = foldArgument.as(BooleanLiteralExprSyntax.self)?.literal,
+            booleanLiteral.text == "true"
+        else {
+            return nil
         }
-        if let booleanLiteral = foldArgument.as(BooleanLiteralExprSyntax.self)?.literal {
-            if booleanLiteral.text == "true" {
-                return """
-                    func preprocess(file: SwiftLintFile) -> SourceFileSyntax? {
-                        file.foldedSyntaxTree
-                    }
-                    """
-            }
-            if booleanLiteral.text == "false" {
-                return ""
-            }
-        }
-        return """
-            func preprocess(file: SwiftLintFile) -> SourceFileSyntax? {
-                if \(foldArgument) { file.foldedSyntaxTree } else { nil }
+
+        return try ExtensionDeclSyntax("""
+            extension \(type) {
+                func preprocess(file: SwiftLintFile) -> SourceFileSyntax? {
+                    file.foldedSyntaxTree
+                }
             }
-            """
+            """)
     }
 }
 
diff --git a/Tests/MacroTests/SwiftSyntaxRuleTests.swift b/Tests/MacroTests/SwiftSyntaxRuleTests.swift
index 6dcdb14b0f..f9dbda1355 100644
--- a/Tests/MacroTests/SwiftSyntaxRuleTests.swift
+++ b/Tests/MacroTests/SwiftSyntaxRuleTests.swift
@@ -20,7 +20,6 @@ final class SwiftSyntaxRuleTests: XCTestCase {
                 func makeVisitor(file: SwiftLintFile) -> ViolationsSyntaxVisitor {
                     Visitor(viewMode: .sourceAccurate)
                 }
-
             }
             """,
             macros: macros
@@ -40,7 +39,6 @@ final class SwiftSyntaxRuleTests: XCTestCase {
                 func makeVisitor(file: SwiftLintFile) -> ViolationsSyntaxVisitor {
                     Visitor(viewMode: .sourceAccurate)
                 }
-
             }
             """,
             macros: macros
@@ -60,6 +58,9 @@ final class SwiftSyntaxRuleTests: XCTestCase {
                 func makeVisitor(file: SwiftLintFile) -> ViolationsSyntaxVisitor {
                     Visitor(viewMode: .sourceAccurate)
                 }
+            }
+
+            extension Hello {
                 func preprocess(file: SwiftLintFile) -> SourceFileSyntax? {
                     file.foldedSyntaxTree
                 }
@@ -70,6 +71,7 @@ final class SwiftSyntaxRuleTests: XCTestCase {
     }
 
     func testArbitraryFoldArgument() {
+        // Silently fail because the macro definition explicitly requires a bool
         assertMacroExpansion(
             """
             @SwiftSyntaxRule(foldExpressions: variable)
@@ -82,13 +84,6 @@ final class SwiftSyntaxRuleTests: XCTestCase {
                 func makeVisitor(file: SwiftLintFile) -> ViolationsSyntaxVisitor {
                     Visitor(viewMode: .sourceAccurate)
                 }
-                func preprocess(file: SwiftLintFile) -> SourceFileSyntax? {
-                    if variable {
-                        file.foldedSyntaxTree
-                    } else {
-                        nil
-                    }
-                }
             }
             """,
             macros: macros