Pass-down -empty-abi-descriptor if evolution is disabled

We should also be able to emit ABI descriptor for modules without evolution.
However, doing so leads us to deserialize more contents from binary modules,
exposing more deserialization issues as a result.

Author: nkcsgexi

Sources/SwiftDriver/Jobs/FrontendJobHelpers.swift

@@ -215,6 +215,15 @@ extension Driver {
       commandLine.appendFlag("-internalize-at-link")
     }
 
+    // ABI descriptors are mostly for modules with -enable-library-evolution.
+    // We should also be able to emit ABI descriptor for modules without evolution.
+    // However, doing so leads us to deserialize more contents from binary modules,
+    // exposing more deserialization issues as a result.
+    if !parsedOptions.hasArgument(.enableLibraryEvolution) &&
+        isFrontendArgSupported(.emptyAbiDescriptor) {
+      commandLine.appendFlag(.emptyAbiDescriptor)
+    }
+
     // Pass down -user-module-version if we are working with a compiler that
     // supports it.
     if let ver = parsedOptions.getLastArgument(.userModuleVersion)?.asSingle,

Tests/SwiftDriverTests/SwiftDriverTests.swift

@@ -566,6 +566,20 @@ final class SwiftDriverTests: XCTestCase {
     }
   }
 
+  func testABIDescriptorOnlyWhenEnableEvolution() throws {
+    let flagName = "-empty-abi-descriptor"
+    try assertNoDriverDiagnostics(args: "swiftc", "foo.swift") { driver in
+      let jobs = try driver.planBuild()
+      let command = jobs[0].commandLine
+      XCTAssertTrue(command.contains(.flag(flagName)))
+    }
+    try assertNoDriverDiagnostics(args: "swiftc", "foo.swift", "-enable-library-evolution") { driver in
+      let jobs = try driver.planBuild()
+      let command = jobs[0].commandLine
+      XCTAssertFalse(command.contains(.flag(flagName)))
+    }
+  }
+
   func testModuleSettings() throws {
     try assertNoDriverDiagnostics(args: "swiftc", "foo.swift") { driver in
       XCTAssertNil(driver.moduleOutputInfo.output)