Make Environment keys case-insensitive on Windows (#174)

This is how the platform treats them, and helps avoid issues where indexing into an Environment dictionary with the wrong casing fails to return a value.

Closes #134

Author: jakepetroules

Sources/Subprocess/Configuration.swift

@@ -401,8 +401,8 @@ 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([String: String])
-        case custom([String: String])
+        case inherit([Key: String])
+        case custom([Key: String])
         #if !os(Windows)
         case rawBytes([[UInt8]])
         #endif
@@ -419,11 +419,11 @@ public struct Environment: Sendable, Hashable {
         return .init(config: .inherit([:]))
     }
     /// Override the provided `newValue` in the existing `Environment`
-    public func updating(_ newValue: [String: String]) -> Self {
+    public func updating(_ newValue: [Key: String]) -> Self {
         return .init(config: .inherit(newValue))
     }
     /// Use custom environment variables
-    public static func custom(_ newValue: [String: String]) -> Self {
+    public static func custom(_ newValue: [Key: String]) -> Self {
         return .init(config: .custom(newValue))
     }
 
@@ -436,6 +436,17 @@ public struct Environment: Sendable, Hashable {
 }
 
 extension Environment: CustomStringConvertible, CustomDebugStringConvertible {
+    /// A key used to access values in an ``Environment``.
+    ///
+    /// This type respects the compiled platform's case sensitivity requirements.
+    public struct Key {
+        public var rawValue: String
+
+        package init(_ rawValue: String) {
+            self.rawValue = rawValue
+        }
+    }
+
     /// A textual representation of the environment.
     public var description: String {
         switch self.config {
@@ -464,9 +475,9 @@ extension Environment: CustomStringConvertible, CustomDebugStringConvertible {
         return self.description
     }
 
-    internal static func currentEnvironmentValues() -> [String: String] {
+    internal static func currentEnvironmentValues() -> [Key: String] {
         return self.withCopiedEnv { environments in
-            var results: [String: String] = [:]
+            var results: [Key: String] = [:]
             for env in environments {
                 let environmentString = String(cString: env)
 
@@ -488,13 +499,76 @@ extension Environment: CustomStringConvertible, CustomDebugStringConvertible {
                 let value = String(
                     environmentString[environmentString.index(after: delimiter)..<environmentString.endIndex]
                 )
-                results[key] = value
+                results[Key(key)] = value
             }
             return results
         }
     }
 }
 
+extension Environment.Key {
+    package static let path: Self = "PATH"
+}
+
+extension Environment.Key: CodingKeyRepresentable {}
+
+extension Environment.Key: Comparable {
+    public static func < (lhs: Self, rhs: Self) -> Bool {
+        // Even on windows use a stable sort order.
+        lhs.rawValue < rhs.rawValue
+    }
+}
+
+extension Environment.Key: CustomStringConvertible {
+    public var description: String { self.rawValue }
+}
+
+extension Environment.Key: Encodable {
+    public func encode(to encoder: any Swift.Encoder) throws {
+        try self.rawValue.encode(to: encoder)
+    }
+}
+
+extension Environment.Key: Equatable {
+    public static func == (_ lhs: Self, _ rhs: Self) -> Bool {
+        #if os(Windows)
+        lhs.rawValue.lowercased() == rhs.rawValue.lowercased()
+        #else
+        lhs.rawValue == rhs.rawValue
+        #endif
+    }
+}
+
+extension Environment.Key: ExpressibleByStringLiteral {
+    public init(stringLiteral rawValue: String) {
+        self.init(rawValue)
+    }
+}
+
+extension Environment.Key: Decodable {
+    public init(from decoder: any Swift.Decoder) throws {
+        self.rawValue = try String(from: decoder)
+    }
+}
+
+extension Environment.Key: Hashable {
+    public func hash(into hasher: inout Hasher) {
+        #if os(Windows)
+        self.rawValue.lowercased().hash(into: &hasher)
+        #else
+        self.rawValue.hash(into: &hasher)
+        #endif
+    }
+}
+
+extension Environment.Key: RawRepresentable {
+    public init?(rawValue: String) {
+        self.rawValue = rawValue
+    }
+}
+
+extension Environment.Key: Sendable {}
+
 // MARK: - TerminationStatus
 
 /// An exit status of a subprocess.

Sources/Subprocess/Platforms/Subprocess+Unix.swift

@@ -145,24 +145,22 @@ extension Execution {
 
 // MARK: - Environment Resolution
 extension Environment {
-    internal static let pathVariableName = "PATH"
-
     internal func pathValue() -> String? {
         switch self.config {
         case .inherit(let overrides):
             // If PATH value exists in overrides, use it
-            if let value = overrides[Self.pathVariableName] {
+            if let value = overrides[.path] {
                 return value
             }
             // Fall back to current process
-            return Self.currentEnvironmentValues()[Self.pathVariableName]
+            return Self.currentEnvironmentValues()[.path]
         case .custom(let fullEnvironment):
-            if let value = fullEnvironment[Self.pathVariableName] {
+            if let value = fullEnvironment[.path] {
                 return value
             }
             return nil
         case .rawBytes(let rawBytesArray):
-            let needle: [UInt8] = Array("\(Self.pathVariableName)=".utf8)
+            let needle: [UInt8] = Array("\(Key.path.rawValue)=".utf8)
             for row in rawBytesArray {
                 guard row.starts(with: needle) else {
                     continue

Sources/Subprocess/Platforms/Subprocess+Windows.swift

@@ -926,13 +926,13 @@ extension Environment {
         switch self.config {
         case .inherit(let overrides):
             // If PATH value exists in overrides, use it
-            if let value = overrides.pathValue() {
+            if let value = overrides[.path] {
                 return value
             }
             // Fall back to current process
-            return Self.currentEnvironmentValues().pathValue()
+            return Self.currentEnvironmentValues()[.path]
         case .custom(let fullEnvironment):
-            if let value = fullEnvironment.pathValue() {
+            if let value = fullEnvironment[.path] {
                 return value
             }
             return nil
@@ -1006,7 +1006,7 @@ extension Configuration {
         intendedWorkingDir: String?
     ) {
         // Prepare environment
-        var env: [String: String] = [:]
+        var env: [Environment.Key: String] = [:]
         switch self.environment.config {
         case .custom(let customValues):
             // Use the custom values directly
@@ -1020,17 +1020,17 @@ extension Configuration {
         }
         // On Windows, the PATH is required in order to locate dlls needed by
         // the process so we should also pass that to the child
-        if env.pathValue() == nil,
-            let parentPath = Environment.currentEnvironmentValues().pathValue()
+        if env[.path] == nil,
+            let parentPath = Environment.currentEnvironmentValues()[.path]
         {
-            env["Path"] = parentPath
+            env[.path] = parentPath
         }
         // The environment string must be terminated by a double
         // null-terminator.  Otherwise, CreateProcess will fail with
         // INVALID_PARMETER.
         let environmentString =
             env.map {
-                $0.key + "=" + $0.value
+                $0.key.rawValue + "=" + $0.value
             }.joined(separator: "\0") + "\0\0"
 
         // Prepare arguments
@@ -1509,11 +1509,4 @@ internal func fillNullTerminatedWideStringBuffer(
     throw SubprocessError.UnderlyingError(rawValue: DWORD(ERROR_INSUFFICIENT_BUFFER))
 }
 
-// Windows environment key is case insensitive
-extension Dictionary where Key == String, Value == String {
-    internal func pathValue() -> String? {
-        return self["Path"] ?? self["PATH"] ?? self["path"]
-    }
-}
-
 #endif // canImport(WinSDK)