Print out details of version mismatch.

Author: David Ungar

Sources/SwiftDriver/IncrementalCompilation/IncrementalDependencyAndInputSetup.swift

@@ -218,9 +218,9 @@ extension IncrementalCompilationState.IncrementalDependencyAndInputSetup {
     do {
       graphIfPresent = try ModuleDependencyGraph.read( from: dependencyGraphPath, info: self)
     }
-    catch ModuleDependencyGraph.ReadError.mismatchedSerializedGraphVersion {
+    catch let ModuleDependencyGraph.ReadError.mismatchedSerializedGraphVersion(expected, read) {
       diagnosticEngine.emit(
-        warning: "Will not do cross-module incremental builds, wrong version of priors at '\(dependencyGraphPath)'")
+        warning: "Will not do cross-module incremental builds, wrong version of priors; expected \(expected) but read \(read) at '\(dependencyGraphPath)'")
       graphIfPresent = nil
     }
     catch {

Sources/SwiftDriver/IncrementalCompilation/ModuleDependencyGraph.swift

@@ -487,7 +487,7 @@ extension ModuleDependencyGraph {
     case badMagic
     case noRecordBlock
     case malformedMetadataRecord
-    case mismatchedSerializedGraphVersion
+    case mismatchedSerializedGraphVersion(expected: Version, read: Version)
     case unexpectedMetadataRecord
     case malformedFingerprintRecord
     case malformedIdentifierRecord
@@ -668,10 +668,15 @@ extension ModuleDependencyGraph {
     try Bitcode.read(bytes: data, using: &visitor)
     guard let major = visitor.majorVersion,
           let minor = visitor.minorVersion,
-          visitor.compilerVersionString != nil,
-          Version(Int(major), Int(minor), 0) == Self.serializedGraphVersion
+          visitor.compilerVersionString != nil
     else {
-      throw ReadError.mismatchedSerializedGraphVersion
+      throw ReadError.malformedMetadataRecord
+    }
+    let readVersion = Version(Int(major), Int(minor), 0)
+    guard readVersion == Self.serializedGraphVersion
+    else {
+      throw ReadError.mismatchedSerializedGraphVersion(
+        expected: Self.serializedGraphVersion, read: readVersion)
     }
     let graph = visitor.finalizeGraph()
     info.reporter?.report("Read dependency graph", path)

Tests/SwiftDriverTests/DependencyGraphSerializationTests.swift

@@ -26,17 +26,20 @@ class DependencyGraphSerializationTests: XCTestCase, ModuleDependencyGraphMocker
     let fs = InMemoryFileSystem()
     let graph = Self.mockGraphCreator.mockUpAGraph()
     let currentVersion = ModuleDependencyGraph.serializedGraphVersion
+    let alteredVersion = currentVersion.withAlteredMinor
     try graph.write(
       to: mockPath,
       on: fs,
       compilerVersion: "Swift 99",
-      mockSerializedGraphVersion: currentVersion.withAlteredMinor)
+      mockSerializedGraphVersion: alteredVersion)
     do {
       _ = try ModuleDependencyGraph.read(from: mockPath,
                                          info: .mock(fileSystem: fs))
       XCTFail("Should have thrown an exception")
     }
-    catch ModuleDependencyGraph.ReadError.mismatchedSerializedGraphVersion {
+    catch let ModuleDependencyGraph.ReadError.mismatchedSerializedGraphVersion(expected, read) {
+      XCTAssertEqual(expected, currentVersion)
+      XCTAssertEqual(read, alteredVersion)
     }
     catch {
       XCTFail("Threw an unexpected exception: \(error.localizedDescription)")

Tests/SwiftDriverTests/IncrementalCompilationTests.swift

@@ -1190,7 +1190,7 @@ extension DiagVerifiable {
     "Incremental compilation: Read dependency graph"
   }
   @DiagsBuilder var couldNotReadPriors: [Diagnostic.Message] {
-      .warning("Will not do cross-module incremental builds, wrong version of priors at '")
+      .warning("Will not do cross-module incremental builds, wrong version of priors; expected")
   }
   // MARK: - dependencies
   @DiagsBuilder func fingerprintChanged(_ aspect: DependencyKey.DeclAspect, _ input: String) -> [Diagnostic.Message] {