Fix module resolver bug exposed by malformed package.json import patterns (#2680)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: andrewbranch <3277153+andrewbranch@users.noreply.github.com>
Co-authored-by: Andrew Branch <andrew@wheream.io>

Author: Copilot

internal/checker/checker.go

@@ -14822,7 +14822,18 @@ func (c *Checker) resolveExternalModule(location *ast.Node, moduleReference stri
 				if ast.FindAncestor(location, ast.IsEmittableImport) != nil {
 					tsExtension := tspath.TryExtractTSExtension(moduleReference)
 					if tsExtension == "" {
-						panic("should be able to extract TS extension from string that passes IsDeclarationFileName")
+						// Fallback: do a best-effort extraction using strings.Contains.
+						// This handles cases where a wildcard pattern matches a TS extension that's
+						// not at the end of the module specifier, e.g., "#/foo.ts.omg" through "#/*.omg": "./src/*"
+						for _, ext := range tspath.SupportedTSExtensionsFlat {
+							if strings.Contains(moduleReference, ext) {
+								tsExtension = ext
+								break
+							}
+						}
+					}
+					if tsExtension == "" {
+						panic("should be able to extract TS extension from string when resolvedUsingTsExtension is true")
 					}
 					c.error(
 						errorNode,

internal/module/resolver.go

@@ -1601,10 +1601,17 @@ func (r *resolutionState) loadFileNameFromPackageJSONField(extensions extensions
 	if extensions&extensionsTypeScript != 0 && tspath.HasImplementationTSFileExtension(candidate) || extensions&extensionsDeclaration != 0 && tspath.IsDeclarationFileName(candidate) {
 		if path, ok := r.tryFile(candidate, onlyRecordFailures); ok {
 			extension := tspath.TryExtractTSExtension(path)
+			// resolvedUsingTsExtension should be true when the pattern ends with * and the
+			// candidate file ends in a TS extension. This means the * matched a TS extension
+			// from the module specifier. For example:
+			// - import "pkg/foo.ts" with pattern "./*" -> true
+			// - import "pkg/foo.ts.omg" with pattern "./*.omg" -> true (star matched .ts)
+			// - import "pkg/foo" with pattern "./*.ts" -> false (extension in pattern, not specifier)
+			resolvedUsingTsExtension := strings.HasSuffix(packageJSONValue, "*") && extension != ""
 			return &resolved{
 				path:                     path,
 				extension:                extension,
-				resolvedUsingTsExtension: packageJSONValue != "" && !strings.HasSuffix(packageJSONValue, extension),
+				resolvedUsingTsExtension: resolvedUsingTsExtension,
 			}
 		}
 		return continueSearching()

testdata/tests/cases/compiler/packageJsonImportsWildcardNoCrash.ts

@@ -0,0 +1,32 @@
+// @noEmit: true
+// @noTypesAndSymbols: true
+// @module: nodenext
+// @moduleResolution: nodenext
+// @filename: src/a.ts
+import * as b from "#/b.";
+
+b.foo();
+
+// @filename: src/b.ts
+export function foo() {}
+
+// @filename: package.json
+{
+    "imports": {
+        "#/*": {
+            "types": "./src/*ts",
+            "default": "./dist/*js"
+        }
+    }
+}
+
+// @filename: tsconfig.json
+{
+    "compilerOptions": {
+        "module": "nodenext",
+        "moduleResolution": "nodenext",
+        "rootDir": "src",
+        "outDir": "dist"
+    },
+    "include": ["src"]
+}

testdata/tests/cases/compiler/packageJsonImportsWildcardTsExtensionError.ts

@@ -0,0 +1,38 @@
+// @noEmit: true
+// @noTypesAndSymbols: true
+// @module: nodenext
+// @moduleResolution: nodenext
+// Test verifies that when a module specifier contains ".ts" that gets matched by a
+// wildcard pattern, resolvedUsingTsExtension is correctly set to true.
+// Example: import "#/foo.ts.omg" with pattern "#/*.omg": "./src/*"
+// The * matches "foo.ts", and when expanded becomes "./src/foo.ts"
+// Since the wildcard matched ".ts" from the specifier, an error should be reported.
+
+// @filename: src/foo.ts
+export function hello() {
+    return "world";
+}
+
+// @filename: src/index.ts
+import { hello } from "#/foo.ts.omg";
+
+hello();
+
+// @filename: package.json
+{
+    "type": "module",
+    "imports": {
+        "#/*.omg": "./src/*"
+    }
+}
+
+// @filename: tsconfig.json
+{
+    "compilerOptions": {
+        "module": "nodenext",
+        "moduleResolution": "nodenext",
+        "rootDir": "src",
+        "outDir": "dist"
+    },
+    "include": ["src"]
+}