From 44796362ed6379954317c9d24911bfbc311e6b6c Mon Sep 17 00:00:00 2001
From: Egor Zhdan <e_zhdan@apple.com>
Date: Tue, 12 Dec 2023 16:28:29 +0100
Subject: [PATCH] [cxx-interop] Do not pass the C++ standard if C++ interop is
 not enabled (#7188)

This fixes the Swift PR testing failures.

### Motivation:

If C++ interop is not enabled, SwiftPM should not pass `-Xcc -std=c++17`
flags.

### Result:

Only pass these flags if C++ interop is enabled.

(cherry picked from commit 351222f5b0d7dc9b1bbdffe6c86c1ec97659b36b)
---
 .../BuildDescription/SwiftTargetBuildDescription.swift    | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/Sources/Build/BuildDescription/SwiftTargetBuildDescription.swift b/Sources/Build/BuildDescription/SwiftTargetBuildDescription.swift
index 2884851691f..67d1d5b2c9e 100644
--- a/Sources/Build/BuildDescription/SwiftTargetBuildDescription.swift
+++ b/Sources/Build/BuildDescription/SwiftTargetBuildDescription.swift
@@ -545,12 +545,14 @@ public final class SwiftTargetBuildDescription {
                 let dependencySwiftFlags = dependencyScope.evaluate(.OTHER_SWIFT_FLAGS)
                 if let interopModeFlag = dependencySwiftFlags.first(where: { $0.hasPrefix("-cxx-interoperability-mode=") }) {
                     args += [interopModeFlag]
+                    if interopModeFlag != "-cxx-interoperability-mode=off" {
+                        if let cxxStandard = self.package.manifest.cxxLanguageStandard {
+                            args += ["-Xcc", "-std=\(cxxStandard)"]
+                        }
+                    }
                     break
                 }
             }
-            if let cxxStandard = self.package.manifest.cxxLanguageStandard {
-                args += ["-Xcc", "-std=\(cxxStandard)"]
-            }
         default: break
         }