Sort for determinism

Author: David Ungar

Sources/SwiftDriver/Incremental Compilation/ModuleDependencyGraph Parts/NodeFinder.swift

@@ -71,6 +71,14 @@ extension ModuleDependencyGraph.NodeFinder {
       .map(fnVerifyingSwiftDeps)
   }
 
+  func forEachUseInOrder(of def: Graph.Node, _ fn: (Graph.Node, Graph.SwiftDeps) -> Void) {
+    var uses = [(Graph.Node, Graph.SwiftDeps)]()
+    forEachUse(of: def) {
+      uses.append(($0, $1))
+    }
+    uses.sorted {$0.0 < $1.0} .forEach { fn($0.0, $0.1) }
+  }
+
   func mappings(of n: Graph.Node) -> [(Graph.SwiftDeps?, DependencyKey)]
   {
     nodeMap.compactMap {

Sources/SwiftDriver/Incremental Compilation/ModuleDependencyGraph Parts/Tracer.swift

@@ -57,7 +57,8 @@ extension ModuleDependencyGraph.Tracer {
   where Nodes.Element == ModuleDependencyGraph.Node
   {
     self.graph = graph
-    self.startingPoints = Array(defs)
+    // Sort so "Tracing" diagnostics are deterministically ordered
+    self.startingPoints = defs.sorted()
     self.currentPathIfTracing = graph.reportIncrementalDecision != nil ? [] : nil
     self.diagnosticEngine = diagnosticEngine
   }
@@ -83,7 +84,7 @@ extension ModuleDependencyGraph.Tracer {
     let pathLengthAfterArrival = traceArrival(at: definition);
 
     // If this use also provides something, follow it
-    graph.nodeFinder.forEachUse(of: definition) { use, _ in
+    graph.nodeFinder.forEachUseInOrder(of: definition) { use, _ in
       findNextPreviouslyUntracedDependent(of: use)
     }
     traceDeparture(pathLengthAfterArrival);

Sources/SwiftDriver/Incremental Compilation/ModuleDependencyGraph.swift

@@ -194,7 +194,7 @@ extension ModuleDependencyGraph {
     // These nodes will depend on the *interface* of the external Decl.
     let key = DependencyKey(interfaceFor: externalSwiftDeps)
     let node = Node(key: key, fingerprint: nil, swiftDeps: nil)
-    nodeFinder.forEachUse(of: node) { use, useSwiftDeps in
+    nodeFinder.forEachUseInOrder(of: node) { use, useSwiftDeps in
       if isUntraced(use) {
         fn(useSwiftDeps)
       }