Allow specifying extra environment variables on a per-job basis

Author: owenv

Sources/SwiftDriver/Execution/JobExecutor.swift

@@ -333,8 +333,8 @@ class ExecuteJobRule: LLBuildRule {
   private func executeJob(_ engine: LLTaskBuildEngine) {
     let context = engine.jobExecutorContext
     let resolver = context.argsResolver
-    let env = context.env
     let job = key.job
+    let env = context.env.merging(job.extraEnvironment, uniquingKeysWith: { $1 })
 
     let value: DriverBuildValue
     var pid = 0

Sources/SwiftDriver/Jobs/Job.swift

@@ -45,6 +45,9 @@ public struct Job: Codable, Equatable {
 
   /// The outputs produced by the job.
   public var outputs: [TypedVirtualPath]
+  
+  /// Any extra environment variables which should be set while running the job.
+  public var extraEnvironment: [String: String]
 
   /// The kind of job.
   public var kind: Kind
@@ -55,14 +58,16 @@ public struct Job: Codable, Equatable {
     commandLine: [ArgTemplate],
     displayInputs: [TypedVirtualPath]? = nil,
     inputs: [TypedVirtualPath],
-    outputs: [TypedVirtualPath]
+    outputs: [TypedVirtualPath],
+    extraEnvironment: [String: String] = [:]
   ) {
     self.kind = kind
     self.tool = tool
     self.commandLine = commandLine
     self.displayInputs = displayInputs ?? []
     self.inputs = inputs
     self.outputs = outputs
+    self.extraEnvironment = extraEnvironment
   }
 }
 
@@ -80,6 +85,13 @@ extension Job: CustomStringConvertible {
       }
     }
 
+    if !self.extraEnvironment.isEmpty {
+      result += " #"
+      for (envVar, val) in extraEnvironment {
+        result += " \(envVar)=\(val)"
+      }
+    }
+
     return result
   }
 }