Add support for swift test list --verbose. (#589)

When `--verbose` is passed to `swift test list`, it is intended that we
handle it by emitting all test IDs including source location info, not
just ambiguous test IDs. This change will be useful to the Swift VSCode
plugin in ensuring that tests are properly identified.

This change also allows you to pass `list` directly to the test
executable instead of `--list-tests`, which simplifies running tests in
Wasm.

### Checklist:

- [x] Code and documentation should follow the style of the [Style
Guide](https://github.com/apple/swift-testing/blob/main/Documentation/StyleGuide.md).
- [x] If public symbols are renamed or modified, DocC references should
be updated.

Author: grynspan

Sources/Testing/ABI/EntryPoints/EntryPoint.swift

@@ -78,7 +78,7 @@ func entryPoint(passing args: __CommandLineArguments_v0?, eventHandler: Event.Ha
       tests = await Array(Test.all)
 
       if args.verbosity > .min {
-        for testID in listTestsForEntryPoint(tests) {
+        for testID in listTestsForEntryPoint(tests, verbosity: args.verbosity) {
           // Print the test ID to stdout (classical CLI behavior.)
 #if SWT_TARGET_OS_APPLE && !SWT_NO_FILE_IO
           try? FileHandle.stdout.write("\(testID)\n")
@@ -130,16 +130,26 @@ func entryPoint(passing args: __CommandLineArguments_v0?, eventHandler: Event.Ha
 ///
 /// - Parameters:
 ///   - tests: The tests to list.
+///   - verbosity: The verbosity level. A level higher than `0` forces the
+///     inclusion of source locations for all tests.
 ///
 /// - Returns: An array of strings representing the IDs of `tests`.
-func listTestsForEntryPoint(_ tests: some Sequence<Test>) -> [String] {
+func listTestsForEntryPoint(_ tests: some Sequence<Test>, verbosity: Int) -> [String] {
   // Filter out hidden tests and test suites. Hidden tests should not generally
   // be presented to the user, and suites (XCTestCase classes) are not included
   // in the equivalent XCTest-based output.
   let tests = tests.lazy
     .filter { !$0.isSuite }
     .filter { !$0.isHidden }
 
+  // Early exit for verbose output (no need to check for ambiguity.)
+  if verbosity > 0 {
+    return tests.lazy
+      .map(\.id)
+      .map(String.init(describing:))
+      .sorted(by: <)
+  }
+
   // Group tests by the name components of the tests' IDs. If the name
   // components of two tests' IDs are ambiguous, present their source locations
   // to disambiguate.
@@ -345,6 +355,10 @@ func parseCommandLineArguments(from args: [String]) throws -> __CommandLineArgum
 
   if args.contains("--list-tests") {
     result.listTests = true
+  } else if args.first == "list" {
+    // Allow the "list" subcommand explicitly in place of "--list-tests". This
+    // makes invocation from e.g. Wasmtime a bit more intuitive/idiomatic.
+    result.listTests = true
   }
 
   // Parallelization (on by default)

Tests/TestingTests/SwiftPMTests.swift

@@ -309,13 +309,25 @@ struct SwiftPMTests {
 
   @Test("list subcommand")
   func list() async throws {
-    let testIDs = await listTestsForEntryPoint(Test.all)
-    let currentTestID = try #require(
-      Test.current
-        .flatMap(\.id.parent)
-        .map(String.init(describing:))
-    )
+    do {
+      let args = try parseCommandLineArguments(from: ["PATH", "--list-tests"])
+      #expect(args.listTests == true)
+    }
+    do {
+      let args = try parseCommandLineArguments(from: ["PATH", "list"])
+      #expect(args.listTests == true)
+    }
+    let testIDs = await listTestsForEntryPoint(Test.all, verbosity: 0)
+    let currentTestID = String(describing: try #require(Test.current?.id.parent))
+    #expect(testIDs.contains(currentTestID))
+  }
+
+  @Test("list --verbose subcommand")
+  func listVerbose() async throws {
+    let testIDs = await listTestsForEntryPoint(Test.all, verbosity: 1)
+    let currentTestID = String(describing: try #require(Test.current?.id))
     #expect(testIDs.contains(currentTestID))
+    #expect(testIDs.allSatisfy { $0.contains(".swift:") })
   }
 
   @Test(