[Build] Enable diagnostic serialization by default for swift modules (#8531)

### Motivation:

Adds a flag and entry into outputs file map per file in a swift module
to emit any diagnostics in serialized form.

This is preliminary work to for future `swift migrate` command that
needs serialized diagnostics to get the fix-its and enables future
improvements like diagnostic de-duplication.

### Modifications:

- Add a new flag to `compileArguments` : `-serialize-diagnostics`
- Add an entry per source file an swift module that presents a path to a
`.dia` file where the diagnostic information should be stored.
- Add a computed property to fetch diagnostic file locations per swift
module

### Result:

The build would now emit serialized diagnostic files for every swift
module.

Author: xedin

Sources/Build/BuildDescription/SwiftModuleBuildDescription.swift

@@ -495,6 +495,8 @@ public final class SwiftModuleBuildDescription {
             args += ["-enable-batch-mode"]
         }
 
+        args += ["-serialize-diagnostics"]
+
         args += self.buildParameters.indexStoreArguments(for: self.target)
         args += self.optimizationArguments
         args += self.testingArguments
@@ -851,6 +853,7 @@ public final class SwiftModuleBuildDescription {
             let sourceFileName = source.basenameWithoutExt
             let partialModulePath = self.tempsPath.appending(component: sourceFileName + "~partial.swiftmodule")
             let swiftDepsPath = self.tempsPath.appending(component: sourceFileName + ".swiftdeps")
+            let diagnosticsPath = self.diagnosticFile(sourceFile: source)
 
             content +=
                 #"""
@@ -872,7 +875,8 @@ public final class SwiftModuleBuildDescription {
                 #"""
                     "\#(objectKey)": "\#(object._nativePathString(escaped: true))",
                     "swiftmodule": "\#(partialModulePath._nativePathString(escaped: true))",
-                    "swift-dependencies": "\#(swiftDepsPath._nativePathString(escaped: true))"
+                    "swift-dependencies": "\#(swiftDepsPath._nativePathString(escaped: true))",
+                    "diagnostics": "\#(diagnosticsPath._nativePathString(escaped: true))"
                   }\#((idx + 1) < sources.count ? "," : "")
 
                 """#
@@ -1055,3 +1059,13 @@ extension SwiftModuleBuildDescription {
         ModuleBuildDescription.swift(self).recursiveDependencies(using: plan)
     }
 }
+
+extension SwiftModuleBuildDescription {
+    package var diagnosticFiles: [AbsolutePath] {
+        self.sources.compactMap { self.diagnosticFile(sourceFile: $0) }
+    }
+
+    private func diagnosticFile(sourceFile: AbsolutePath) -> AbsolutePath {
+        self.tempsPath.appending(component: "\(sourceFile.basenameWithoutExt).dia")
+    }
+}

Tests/BuildTests/BuildPlanTests.swift

@@ -33,6 +33,7 @@ import Workspace
 import XCTest
 
 import struct TSCBasic.ByteString
+import func TSCBasic.withTemporaryFile
 
 import enum TSCUtility.Diagnostics
 
@@ -785,6 +786,7 @@ class BuildPlanTestCase: BuildSystemProviderTestCase {
             exe,
             [
                 "-enable-batch-mode",
+                "-serialize-diagnostics",
                 "-Onone",
                 "-enable-testing",
                 .equal(self.j),
@@ -803,6 +805,7 @@ class BuildPlanTestCase: BuildSystemProviderTestCase {
             lib,
             [
                 "-enable-batch-mode",
+                "-serialize-diagnostics",
                 "-Onone",
                 "-enable-testing",
                 .equal(self.j),
@@ -1854,6 +1857,7 @@ class BuildPlanTestCase: BuildSystemProviderTestCase {
             [
                 .anySequence,
                 "-enable-batch-mode",
+                "-serialize-diagnostics",
                 "-Onone",
                 "-enable-testing",
                 .equal(self.j),
@@ -2355,6 +2359,7 @@ class BuildPlanTestCase: BuildSystemProviderTestCase {
             [
                 .anySequence,
                 "-enable-batch-mode",
+                "-serialize-diagnostics",
                 "-Onone",
                 "-enable-testing",
                 .equal(self.j),
@@ -2374,6 +2379,7 @@ class BuildPlanTestCase: BuildSystemProviderTestCase {
             [
                 .anySequence,
                 "-enable-batch-mode",
+                "-serialize-diagnostics",
                 "-Onone",
                 "-enable-testing",
                 "-Xfrontend",
@@ -2852,6 +2858,7 @@ class BuildPlanTestCase: BuildSystemProviderTestCase {
         let matchText = try result.moduleBuildDescription(for: "exe").swift().compileArguments()
         let assertionText: [StringPattern] = [
             "-enable-batch-mode",
+            "-serialize-diagnostics",
             "-Onone",
             "-enable-testing",
             .equal(self.j),
@@ -3153,6 +3160,7 @@ class BuildPlanTestCase: BuildSystemProviderTestCase {
             exe,
             [
                 "-enable-batch-mode",
+                "-serialize-diagnostics",
                 "-Onone",
                 "-enable-testing",
                 .equal(self.j),
@@ -3171,6 +3179,7 @@ class BuildPlanTestCase: BuildSystemProviderTestCase {
             lib,
             [
                 "-enable-batch-mode",
+                "-serialize-diagnostics",
                 "-Onone",
                 "-enable-testing",
                 .equal(self.j),
@@ -3811,6 +3820,7 @@ class BuildPlanTestCase: BuildSystemProviderTestCase {
         let exe = try result.moduleBuildDescription(for: "exe").swift().compileArguments()
         XCTAssertMatch(exe, [
             "-enable-batch-mode",
+            "-serialize-diagnostics",
             "-Onone",
             "-enable-testing",
             .equal(self.j),
@@ -6975,6 +6985,59 @@ class BuildPlanTestCase: BuildSystemProviderTestCase {
         print(myLib.additionalFlags)
         XCTAssertFalse(myLib.additionalFlags.contains(where: { $0.contains("-tool/include")}), "flags shouldn't contain tools items")
     }
+
+    func testDiagnosticsAreMentionedInOutputsFileMap() async throws {
+        let fs = InMemoryFileSystem(
+            emptyFiles:
+            "/Pkg/Sources/exe/main.swift",
+            "/Pkg/Sources/exe/aux.swift",
+            "/Pkg/Sources/lib/lib.swift"
+        )
+
+        let observability = ObservabilitySystem.makeForTesting()
+        let graph = try loadModulesGraph(
+            fileSystem: fs,
+            manifests: [
+                Manifest.createRootManifest(
+                    displayName: "Pkg",
+                    path: "/Pkg",
+                    targets: [
+                        TargetDescription(name: "exe", dependencies: ["lib"]),
+                        TargetDescription(name: "lib", dependencies: []),
+                    ]
+                ),
+            ],
+            observabilityScope: observability.topScope
+        )
+        XCTAssertNoDiagnostics(observability.diagnostics)
+
+        let plan = try await mockBuildPlan(
+            graph: graph,
+            linkingParameters: .init(
+                shouldLinkStaticSwiftStdlib: true
+            ),
+            fileSystem: fs,
+            observabilityScope: observability.topScope
+        )
+        let result = try BuildPlanResult(plan: plan)
+
+        result.checkProductsCount(1)
+        result.checkTargetsCount(2)
+
+        for module in result.targetMap {
+            let buildDescription = try module.swift()
+
+            try withTemporaryFile { file in
+                try buildDescription.writeOutputFileMap(to: .init(file.path.pathString))
+
+                let fileMap = try String(bytes: fs.readFileContents(file.path).contents, encoding: .utf8)
+
+                for diagnosticFile in buildDescription.diagnosticFiles {
+                    XCTAssertMatch(fileMap, .contains(diagnosticFile.pathString))
+                }
+            }
+        }
+    }
 }
 
 class BuildPlanNativeTests: BuildPlanTestCase {

Tests/BuildTests/CrossCompilationBuildPlanTests.swift

@@ -178,7 +178,7 @@ final class CrossCompilationBuildPlanTests: XCTestCase {
         XCTAssertMatch(
             exe,
             [
-                "-enable-batch-mode", "-Onone", "-enable-testing",
+                "-enable-batch-mode", "-serialize-diagnostics", "-Onone", "-enable-testing",
                 "-j3", "-DSWIFT_PACKAGE", "-DDEBUG", "-Xcc",
                 "-fmodule-map-file=\(buildPath.appending(components: "lib.build", "module.modulemap"))",
                 "-Xcc", "-I", "-Xcc", "\(pkgPath.appending(components: "Sources", "lib", "include"))",