Add test cases for invalid submodule selectors

And add newline-sensitive behavior matching other uses of module selectors.

Author: beccadax

Sources/SwiftParser/Names.swift

@@ -106,7 +106,7 @@ extension TokenConsumer {
     }
 
     var extra: [Token] = []
-    while self.isAtModuleSelector() {
+    while !self.currentToken.isAtStartOfLine && self.isAtModuleSelector() {
       if !self.at(.colonColon) {
         extra.append(self.consumeAnyToken())
       }

Tests/SwiftParserTest/translated/ModuleSelectorTests.swift

@@ -10,7 +10,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// This test file has been translated from swift/test/NameLookup/module_selector.swift
+// This test file has been translated from swift/test/Parse/module_selector.swift
 
 @_spi(ExperimentalLanguageFeatures) import SwiftParser
 @_spi(ExperimentalLanguageFeatures) import SwiftSyntax
@@ -2257,6 +2257,41 @@ final class ModuleSelectorTests: ParserTestCase {
       )
     )
   }
+
+  func testModuleSelectorSubmodule() {
+    assertParse(
+      "_ = Foundation::1️⃣NSData::NSData()",
+      diagnostics: [
+        DiagnosticSpec(message: "unexpected code 'NSData::' in module selector")
+      ]
+    )
+
+    assertParse(
+      "_ = Foundation::1️⃣NSData::Fnord::NSData()",
+      diagnostics: [
+        DiagnosticSpec(message: "unexpected code 'NSData::Fnord::' in module selector")
+      ]
+    )
+
+    assertParse(
+      """
+      _ = Foundation::1️⃣NSData::2️⃣
+      Fnord::NSData()
+      """,
+      diagnostics: [
+        DiagnosticSpec(message: "unexpected code 'NSData::' in module selector"),
+        DiagnosticSpec(
+          locationMarker: "2️⃣",
+          message: "expected identifier",
+          fixIts: ["insert identifier"]
+        ),
+      ],
+      fixedSource: """
+        _ = Foundation::NSData::<#identifier#>
+        Fnord::NSData()
+        """
+    )
+  }
 }
 
 // MARK: - Syntax tree construction helpers