Merge pull request #151 from apple/fix-testBrewPrefix-unit-test-failure

Fix a unit test (`testBrewPrefix`) that only fails when running all the tests

Author: abertelrud

Sources/TSCUtility/PkgConfig.swift

@@ -33,6 +33,9 @@ public struct PCFileFinder {
     let diagnostics: DiagnosticsEngine
 
     /// Cached results of locations `pkg-config` will search for `.pc` files
+    /// FIXME: This shouldn't use a static variable, since the first lookup
+    /// will cache the result of whatever `brewPrefix` was passed in.  It is
+    /// also not threadsafe.
     public private(set) static var pkgConfigPaths: [AbsolutePath]? // FIXME: @testable(internal)
     private static var shouldEmitPkgConfigPathsDiagnostic = false
 
@@ -70,6 +73,14 @@ public struct PCFileFinder {
             }
         }
     }
+    
+    /// Reset the cached `pkgConfigPaths` property, so that it will be evaluated
+    /// again when instantiating a `PCFileFinder()`.  This is intended only for
+    /// use by testing.  This is a temporary workaround for the use of a static
+    /// variable by this class.
+    internal static func resetCachedPkgConfigPaths() {
+        PCFileFinder.pkgConfigPaths = nil
+    }
 
     public func locatePCFile(
         name: String,

Tests/TSCUtilityTests/PkgConfigParserTests.swift

@@ -1,7 +1,7 @@
 /*
  This source file is part of the Swift.org open source project
 
- Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
+ Copyright (c) 2014 - 2020 Apple Inc. and the Swift project authors
  Licensed under Apache License v2.0 with Runtime Library Exception
 
  See http://swift.org/LICENSE.txt for license information
@@ -12,7 +12,7 @@ import XCTest
 import TSCBasic
 import TSCTestSupport
 
-import TSCUtility
+@testable import TSCUtility
 
 final class PkgConfigParserTests: XCTestCase {
 
@@ -91,6 +91,9 @@ final class PkgConfigParserTests: XCTestCase {
 
     /// Test custom search path get higher priority for locating pc files.
     func testCustomPcFileSearchPath() throws {
+        /// Temporary workaround for PCFileFinder's use of static variables.
+        PCFileFinder.resetCachedPkgConfigPaths()
+
         let diagnostics = DiagnosticsEngine()
 
         let fs = InMemoryFileSystem(emptyFiles:
@@ -109,6 +112,9 @@ final class PkgConfigParserTests: XCTestCase {
     }
 
     func testBrewPrefix() throws {
+        /// Temporary workaround for PCFileFinder's use of static variables.
+        PCFileFinder.resetCachedPkgConfigPaths()
+
         try testWithTemporaryDirectory { tmpdir in
             let fakePkgConfig = tmpdir.appending(components: "bin", "pkg-config")
             try localFileSystem.createDirectory(fakePkgConfig.parentDirectory)