Define sources for mixed package tests inline with the tests

Sources/SKTestSupport/INPUTS/MixedPackage/Package.swift

@@ -1,10 +0,0 @@
-// swift-tools-version:5.1
-import PackageDescription
-
-let package = Package(
-  name: "pkg",
-  targets: [
-    .target(name: "lib", dependencies: []),
-    .target(name: "clib", dependencies: []),
-  ]
-)

Sources/SKTestSupport/INPUTS/MixedPackage/Sources/clib/clib.c

@@ -1,3 +0,0 @@
-#include "clib.h"
-
-void clib_func(void) {/*clib_func:body*/}

Sources/SKTestSupport/INPUTS/MixedPackage/Sources/clib/include/clib.h

@@ -1,7 +0,0 @@
-#ifndef CLIB_H
-#define CLIB_H
-
-void clib_func(void);
-void clib_other(void);
-
-#endif // CLIB_H

Sources/SKTestSupport/INPUTS/MixedPackage/Sources/lib/lib.swift

@@ -1,5 +0,0 @@
-public struct Lib {
-  public func foo() {}
-  public init() {}
-}
-/*lib.swift:toplevel*/

Sources/SKTestSupport/MultiFileTestWorkspace.swift

@@ -17,10 +17,10 @@ import SKCore
 /// The location of a test file within test workspace.
 public struct RelativeFileLocation: Hashable, ExpressibleByStringLiteral {
   /// The subdirectories in which the file is located.
-  fileprivate let directories: [String]
+  let directories: [String]
 
   /// The file's name.
-  fileprivate let fileName: String
+  let fileName: String
 
   public init(directories: [String] = [], _ fileName: String) {
     self.directories = directories

Sources/SKTestSupport/SwiftPMTestWorkspace.swift

@@ -36,14 +36,22 @@ public class SwiftPMTestWorkspace: MultiFileTestWorkspace {
   ///
   /// If `index` is `true`, then the package will be built, indexing all modules within the package.
   public init(
-    files: [String: String],
+    files: [RelativeFileLocation: String],
     manifest: String = SwiftPMTestWorkspace.defaultPackageManifest,
     build: Bool = false,
     testName: String = #function
   ) async throws {
     var filesByPath: [RelativeFileLocation: String] = [:]
-    for (fileName, contents) in files {
-      filesByPath[RelativeFileLocation(directories: ["Sources", "MyLibrary"], fileName)] = contents
+    for (fileLocation, contents) in files {
+      let directories =
+        if fileLocation.directories.isEmpty {
+          ["Sources", "MyLibrary"]
+        } else if fileLocation.directories.first != "Sources" {
+          ["Sources"] + fileLocation.directories
+        } else {
+          fileLocation.directories
+        }
+      filesByPath[RelativeFileLocation(directories: directories, fileLocation.fileName)] = contents
     }
     filesByPath["Package.swift"] = manifest
     try await super.init(

Tests/SourceKitLSPTests/WorkspaceTests.swift

@@ -238,18 +238,57 @@ final class WorkspaceTests: XCTestCase {
   }
 
   func testMixedPackage() async throws {
-    guard let ws = try await staticSourceKitSwiftPMWorkspace(name: "MixedPackage") else { return }
-    try ws.buildAndIndex()
+    let ws = try await SwiftPMTestWorkspace(
+      files: [
+        "clib/include/clib.h": """
+        #ifndef CLIB_H
+        #define CLIB_H
 
-    let cLoc = ws.testLoc("clib_func:body")
-    let swiftLoc = ws.testLoc("lib.swift:toplevel")
+        void clib_func(void);
+        void clib_other(void);
 
-    try ws.openDocument(swiftLoc.url, language: .swift)
-    try ws.openDocument(cLoc.url, language: .c)
+        #endif // CLIB_H
+        """,
+        "clib/clib.c": """
+        #include "clib.h"
 
-    await assertNoThrow {
-      _ = try await ws.testClient.send(CompletionRequest(textDocument: cLoc.docIdentifier, position: cLoc.position))
-    }
+        void clib_func(void) {1️⃣}
+        """,
+        "lib/lib.swift": """
+        public struct Lib {
+          public func foo() {}
+          public init() {}
+        }
+        2️⃣
+        """,
+      ],
+      manifest: """
+        // swift-tools-version: 5.7
+
+        import PackageDescription
+
+        let package = Package(
+          name: "MyLibrary",
+          targets: [
+            .target(name: "lib", dependencies: []),
+            .target(name: "clib", dependencies: []),
+          ]
+        )
+        """
+    )
+
+    let (swiftUri, swiftPositions) = try ws.openDocument("lib.swift")
+    let (cUri, cPositions) = try ws.openDocument("clib.c")
+
+    let cCompletions = try await ws.testClient.send(
+      CompletionRequest(textDocument: TextDocumentIdentifier(cUri), position: cPositions["1️⃣"])
+    )
+    XCTAssertGreaterThanOrEqual(cCompletions.items.count, 0)
+
+    let swiftCompletions = try await ws.testClient.send(
+      CompletionRequest(textDocument: TextDocumentIdentifier(swiftUri), position: swiftPositions["2️⃣"])
+    )
+    XCTAssertGreaterThanOrEqual(swiftCompletions.items.count, 0)
   }
 
   func testChangeWorkspaceFolders() async throws {