Fix normalizePath rooting a relative path that begins with ./ followed by a slash

src/compiler/path.ts

@@ -736,7 +736,10 @@ function simpleNormalizePath(path: string): string | undefined {
     }
     // Some paths only require cleanup of `/./` or leading `./`
     let simplified = path.replace(/\/\.\//g, "/");
-    if (simplified.startsWith("./")) {
+    // Only strip a leading `./` when it is an actual `.` segment, not the
+    // start of a `.//` sequence where the second slash is a redundant
+    // separator (stripping there would turn a relative path into a rooted one).
+    if (simplified.startsWith("./") && simplified.charCodeAt(2) !== CharacterCodes.slash) {
         simplified = simplified.slice(2);
     }
     if (simplified !== path) {

src/testRunner/unittests/paths.ts

@@ -318,6 +318,10 @@ describe("unittests:: core paths", () => {
         assert.strictEqual(ts.getNormalizedAbsolutePath(".", ""), "");
         assert.strictEqual(ts.getNormalizedAbsolutePath("./", ""), "");
         assert.strictEqual(ts.getNormalizedAbsolutePath("./a", ""), "a");
+        // A `./` followed by a redundant separator must stay relative, not become rooted.
+        assert.strictEqual(ts.getNormalizedAbsolutePath(".//a", ""), "a");
+        assert.strictEqual(ts.getNormalizedAbsolutePath(".//a/b", ""), "a/b");
+        assert.strictEqual(ts.getNormalizedAbsolutePath("././/a", ""), "a");
         // Strangely, these do not normalize to the empty string.
         assert.strictEqual(ts.getNormalizedAbsolutePath("..", ""), "..");
         assert.strictEqual(ts.getNormalizedAbsolutePath("../", ""), "..");