[xcodegen] Clean up file extension handling

Factor out `FileExtension.matches` and add some tests.

Author: hamishknight

utils/swift-xcodegen/Sources/SwiftXcodeGen/Path/AnyPath.swift

@@ -74,9 +74,3 @@ extension AnyPath: ExpressibleByArgument {
     self.init(rawPath)
   }
 }
-
-extension StringProtocol {
-  func hasExtension(_ ext: FileExtension) -> Bool {
-    FilePath(String(self)).extension == ext.rawValue
-  }
-}

utils/swift-xcodegen/Sources/SwiftXcodeGen/Path/PathProtocol.swift

@@ -68,16 +68,11 @@ public extension PathProtocol {
     return RelativePath(result)
   }
 
-  func hasExtension(_ ext: FileExtension) -> Bool {
-    storage.extension == ext.rawValue
-  }
   func hasExtension(_ exts: FileExtension...) -> Bool {
     // Note that querying `.extension` involves re-parsing, so only do it
     // once here.
-    guard let ext = storage.extension else { return false }
-    return exts.contains(where: {
-      ext.compare($0.rawValue, options: .caseInsensitive) == .orderedSame
-    })
+    guard let pathExt = storage.extension else { return false }
+    return exts.contains(where: { $0.matches(pathExt) })
   }
 
   func starts(with other: Self) -> Bool {
@@ -158,3 +153,16 @@ extension Collection where Element: PathProtocol {
     return result == first ? result.parentDir : result
   }
 }
+
+extension StringProtocol {
+  func hasExtension(_ exts: FileExtension...) -> Bool {
+    guard let pathExt = FilePath(String(self)).extension else { return false }
+    return exts.contains(where: { $0.matches(pathExt) })
+  }
+}
+
+extension FileExtension {
+  func matches(_ extStr: String) -> Bool {
+    rawValue.compare(extStr, options: .caseInsensitive) == .orderedSame
+  }
+}

utils/swift-xcodegen/Tests/SwiftXcodeGenTest/PathTests.swift

@@ -37,4 +37,28 @@ class PathTests: XCTestCase {
     XCTAssertEqual(RelativePath("foo/bar").dropLast(2), "")
     XCTAssertEqual(RelativePath("foo/bar").dropLast(5), "")
   }
+
+  func testExtension() throws {
+    func match(
+      _ ext: FileExtension, with path: String,
+      value: Bool = true, file: StaticString = #file, line: UInt = #line
+    ) {
+      XCTAssert(path.hasExtension(ext) == value, file: file, line: line)
+      XCTAssert(AnyPath(path).hasExtension(ext) == value, file: file, line: line)
+    }
+    match(.swift, with: "x.swift")
+    match(.swift, with: "/x.swift")
+    match(.swift, with: ".swift", value: false)
+    match(.swift, with: "/.swift", value: false)
+
+    match(.swift, with: "x.SWIFT")
+    match(.swift, with: "/x.SWIFT")
+    match(.swift, with: ".SWIFT", value: false)
+    match(.swift, with: "/.SWIFT", value: false)
+
+    match(.swift, with: "x.swiftx", value: false)
+
+    XCTAssert("x.sWift".hasExtension(.asm, .swift))
+    XCTAssert(AnyPath("x.sWift").hasExtension(.asm, .swift))
+  }
 }