From 1a480b470ffb440506cd842250dc58dd4109f768 Mon Sep 17 00:00:00 2001
From: Evan Wilde <etceterawilde@gmail.com>
Date: Mon, 13 May 2024 09:28:06 -0700
Subject: [PATCH 1/2] Allow setting the clang++ environment variable

'+' isn't allowed in environment variable names so it's impossible to
set the Clang++ executable at the moment. Replace `+` with `X` so that
we can set `SWIFT_DRIVER_CLANGXX_EXEC` to set the clang++ executable.
---
 Sources/SwiftDriver/Toolchains/Toolchain.swift | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/Sources/SwiftDriver/Toolchains/Toolchain.swift b/Sources/SwiftDriver/Toolchains/Toolchain.swift
index 8d84b503f..214ff8597 100644
--- a/Sources/SwiftDriver/Toolchains/Toolchain.swift
+++ b/Sources/SwiftDriver/Toolchains/Toolchain.swift
@@ -196,7 +196,10 @@ extension Toolchain {
 
   /// - Returns: String in the form of: `SWIFT_DRIVER_TOOLNAME_EXEC`
   private func envVarName(for toolName: String) -> String {
-    let lookupName = toolName.replacingOccurrences(of: "-", with: "_").uppercased()
+    let lookupName = toolName
+        .replacingOccurrences(of: "-", with: "_")
+        .replacingOccurrences(of: "+", with: "X")
+        .uppercased()
     return "SWIFT_DRIVER_\(lookupName)_EXEC"
   }
 

From 43c114425774883fec4e5f67a83f5d9788572eea Mon Sep 17 00:00:00 2001
From: Evan Wilde <etceterawilde@gmail.com>
Date: Mon, 13 May 2024 11:21:02 -0700
Subject: [PATCH 2/2] Test: Check clang overrides

Check that the clang override environment variables actually do
something. Note that clang++ is only used to link on non-Darwin
platforms when the interop mode is swift-5.9.
---
 Tests/SwiftDriverTests/SwiftDriverTests.swift | 35 +++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/Tests/SwiftDriverTests/SwiftDriverTests.swift b/Tests/SwiftDriverTests/SwiftDriverTests.swift
index 64f076f25..40f24fca8 100644
--- a/Tests/SwiftDriverTests/SwiftDriverTests.swift
+++ b/Tests/SwiftDriverTests/SwiftDriverTests.swift
@@ -6823,6 +6823,41 @@ final class SwiftDriverTests: XCTestCase {
     XCTAssertEqual(jobs.first!.tool.name, swiftHelp.pathString)
   }
 
+  func testSwiftClangOverride() throws {
+    var env = ProcessEnv.vars
+    let swiftClang = try AbsolutePath(validating: "/A/Path/swift-clang")
+    env["SWIFT_DRIVER_CLANG_EXEC"] = swiftClang.pathString
+
+    var driver = try Driver(
+      args: ["swiftc", "-emit-library", "foo.swift", "bar.o", "-o", "foo.l"],
+      env: env)
+    let jobs = try driver.planBuild()
+    XCTAssertEqual(jobs.count, 2)
+    let linkJob = jobs[1]
+    XCTAssertEqual(linkJob.tool.name, swiftClang.pathString)
+  }
+
+  func testSwiftClangxxOverride() throws {
+#if os(iOS) || os(macOS) || os(tvOS) || os(watchOS)
+      throw XCTSkip("Darwin always uses `clang` to link")
+#else
+    var env = ProcessEnv.vars
+    let swiftClang = try AbsolutePath(validating: "/A/Path/swift-clang")
+    let swiftClangxx = try AbsolutePath(validating: "/A/Path/swift-clang++")
+    env["SWIFT_DRIVER_CLANG_EXEC"] = swiftClang.pathString
+    env["SWIFT_DRIVER_CLANGXX_EXEC"] = swiftClangxx.pathString
+
+    var driver = try Driver(
+      args: ["swiftc", "-cxx-interoperability-mode=swift-5.9", "-emit-library",
+             "foo.swift", "bar.o", "-o", "foo.l"],
+      env: env)
+
+    let jobs = try driver.planBuild()
+    let linkJob = jobs.last!
+    XCTAssertEqual(linkJob.tool.name, swiftClangxx.pathString)
+#endif
+  }
+
   func testSourceInfoFileEmitOption() throws {
     // implicit
     do {