Change Environment.updating to accept [Key: String?]. A nil value removes the corresponding key from being inherited by child processes (#193)

Author: iCharlesHu

Sources/Subprocess/Configuration.swift

@@ -401,7 +401,7 @@ extension Arguments: CustomStringConvertible, CustomDebugStringConvertible {
 /// A set of environment variables to use when executing the subprocess.
 public struct Environment: Sendable, Hashable {
     internal enum Configuration: Sendable, Hashable {
-        case inherit([Key: String])
+        case inherit([Key: String?])
         case custom([Key: String])
         #if !os(Windows)
         case rawBytes([[UInt8]])
@@ -418,8 +418,10 @@ public struct Environment: Sendable, Hashable {
     public static var inherit: Self {
         return .init(config: .inherit([:]))
     }
-    /// Override the provided `newValue` in the existing `Environment`
-    public func updating(_ newValue: [Key: String]) -> Self {
+    /// Override the provided `newValue` in the existing `Environment`.
+    /// Keys with `nil` values in `newValue` will be removed from existing
+    /// `Environment` before passing to child process.
+    public func updating(_ newValue: [Key: String?]) -> Self {
         return .init(config: .inherit(newValue))
     }
     /// Use custom environment variables

Sources/Subprocess/Platforms/Subprocess+Unix.swift

@@ -203,9 +203,13 @@ extension Environment {
             var current = Self.currentEnvironmentValues()
             for (key, value) in updates {
                 // Remove the value from current to override it
+                // If the `value` is nil, we effectively "unset"
+                // this value from current
                 current.removeValue(forKey: key)
-                let fullString = "\(key)=\(value)"
-                env.append(strdup(fullString))
+                if let value {
+                    let fullString = "\(key)=\(value)"
+                    env.append(strdup(fullString))
+                }
             }
             // Add the rest of `current` to env
             for (key, value) in current {

Sources/Subprocess/Platforms/Subprocess+Windows.swift

@@ -1015,7 +1015,13 @@ extension Configuration {
             // Combine current environment
             env = Environment.currentEnvironmentValues()
             for (key, value) in updateValues {
-                env.updateValue(value, forKey: key)
+                if let value {
+                    // Update env with ew value
+                    env.updateValue(value, forKey: key)
+                } else {
+                    // If `value` is `nil`, unset this value from env
+                    env.removeValue(forKey: key)
+                }
             }
         }
         // On Windows, the PATH is required in order to locate dlls needed by

Tests/SubprocessTests/IntegrationTests.swift

@@ -310,6 +310,82 @@ extension SubprocessIntegrationTests {
         )
     }
 
+    @Test func testEnvironmentInheritOverrideUnsetValue() async throws {
+        #if os(Windows)
+        // First insert our dummy environment variable
+        "SubprocessTest".withCString(encodedAs: UTF16.self) { keyW in
+            "value".withCString(encodedAs: UTF16.self) { valueW in
+                SetEnvironmentVariableW(keyW, valueW)
+            }
+        }
+        defer {
+            "SubprocessTest".withCString(encodedAs: UTF16.self) { keyW in
+                SetEnvironmentVariableW(keyW, nil)
+            }
+        }
+
+        var setup = TestSetup(
+            executable: .name("cmd.exe"),
+            arguments: ["/c", "echo %SubprocessTest%"],
+            environment: .inherit
+        )
+        #else
+        // First insert our dummy environment variable
+        setenv("SubprocessTest", "value", 1);
+        defer {
+            unsetenv("SubprocessTest")
+        }
+
+        var setup = TestSetup(
+            executable: .path("/bin/sh"),
+            arguments: ["-c", "printenv SubprocessTest"],
+            environment: .inherit
+        )
+        #endif
+        // First make sure child process actually inherited SubprocessTest
+        let result = try await _run(
+            setup,
+            input: .none,
+            output: .string(limit: 32),
+            error: .discarded
+        )
+        #expect(result.terminationStatus.isSuccess)
+        // rdar://138670128
+        // https://github.com/swiftlang/swift/issues/77235
+        let output = result.standardOutput?
+            .trimmingNewLineAndQuotes()
+        #expect(output == "value")
+
+        // Now make sure we can remove `SubprocessTest`
+        #if os(Windows)
+        setup = TestSetup(
+            executable: .name("cmd.exe"),
+            arguments: ["/c", "echo %SubprocessTest%"],
+            environment: .inherit
+                .updating(["SubprocessTest": nil])
+        )
+        #else
+        setup = TestSetup(
+            executable: .path("/bin/sh"),
+            arguments: ["-c", "printenv SubprocessTest"],
+            environment: .inherit
+                .updating(["SubprocessTest": nil])
+        )
+        #endif
+        let result2 = try await _run(
+            setup,
+            input: .none,
+            output: .string(limit: 32),
+            error: .discarded
+        )
+        // The new echo/printenv should not find `SubprocessTest`
+        #if os(Windows)
+        #expect(result2.standardOutput?.trimmingNewLineAndQuotes() == "%SubprocessTest%")
+        #else
+        #expect(result2.terminationStatus == .exited(1))
+        #endif
+    }
+
     @Test(
         // Make sure we don't accidentally have this dummy value
         .enabled(if: ProcessInfo.processInfo.environment["SystemRoot"] != nil)