Fix handling of empty 'types', 'typings', etc. fields in package.json (#31539)

Author: rbuckton

src/compiler/diagnosticMessages.json

@@ -3927,6 +3927,10 @@
         "category": "Message",
         "code": 6219
     },
+    "'package.json' had a falsy '{0}' field.": {
+        "category": "Message",
+        "code": 6220
+    },
 
     "Projects to reference": {
         "category": "Message",

src/compiler/moduleNameResolver.ts

@@ -141,7 +141,15 @@ namespace ts {
 
     function readPackageJsonPathField<K extends "typings" | "types" | "main" | "tsconfig">(jsonContent: PackageJson, fieldName: K, baseDirectory: string, state: ModuleResolutionState): PackageJson[K] | undefined {
         const fileName = readPackageJsonField(jsonContent, fieldName, "string", state);
-        if (fileName === undefined) return;
+        if (fileName === undefined) {
+            return;
+        }
+        if (!fileName) {
+            if (state.traceEnabled) {
+                trace(state.host, Diagnostics.package_json_had_a_falsy_0_field, fieldName);
+            }
+            return;
+        }
         const path = normalizePath(combinePaths(baseDirectory, fileName));
         if (state.traceEnabled) {
             trace(state.host, Diagnostics.package_json_has_0_field_1_that_references_2, fieldName, fileName, path);

tests/baselines/reference/typesVersions.emptyTypes.js

@@ -0,0 +1,20 @@
+//// [tests/cases/conformance/moduleResolution/typesVersions.emptyTypes.ts] ////
+
+//// [package.json]
+{
+    "types": "",
+    "typesVersions": {
+        ">=3.1.0-0": { "*" : ["ts3.1/*"] }
+    }
+}
+
+//// [index.d.ts]
+export const a = 0;
+
+//// [user.ts]
+import { a } from "a";
+
+
+//// [user.js]
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });

tests/baselines/reference/typesVersions.emptyTypes.symbols

@@ -0,0 +1,8 @@
+=== /a/ts3.1/index.d.ts ===
+export const a = 0;
+>a : Symbol(a, Decl(index.d.ts, 0, 12))
+
+=== /b/user.ts ===
+import { a } from "a";
+>a : Symbol(a, Decl(user.ts, 0, 8))
+

tests/baselines/reference/typesVersions.emptyTypes.trace.json

@@ -0,0 +1,24 @@
+[
+    "======== Resolving module 'a' from '/b/user.ts'. ========",
+    "Module resolution kind is not specified, using 'NodeJs'.",
+    "'baseUrl' option is set to '/', using this value to resolve non-relative module name 'a'.",
+    "Resolving module name 'a' relative to base url '/' - '/a'.",
+    "Loading module as file / folder, candidate module location '/a', target file type 'TypeScript'.",
+    "File '/a.ts' does not exist.",
+    "File '/a.tsx' does not exist.",
+    "File '/a.d.ts' does not exist.",
+    "Found 'package.json' at '/a/package.json'.",
+    "'package.json' has a 'typesVersions' field with version-specific path mappings.",
+    "'package.json' does not have a 'typings' field.",
+    "'package.json' had a falsy 'types' field.",
+    "'package.json' does not have a 'main' field.",
+    "'package.json' has a 'typesVersions' entry '>=3.1.0-0' that matches compiler version '3.1.0-dev', looking for a pattern to match module name 'index'.",
+    "Module name 'index', matched pattern '*'.",
+    "Trying substitution 'ts3.1/*', candidate module location: 'ts3.1/index'.",
+    "File '/a/ts3.1/index' does not exist.",
+    "Loading module as file / folder, candidate module location '/a/ts3.1/index', target file type 'TypeScript'.",
+    "File '/a/ts3.1/index.ts' does not exist.",
+    "File '/a/ts3.1/index.tsx' does not exist.",
+    "File '/a/ts3.1/index.d.ts' exist - use it as a name resolution result.",
+    "======== Module name 'a' was successfully resolved to '/a/ts3.1/index.d.ts'. ========"
+]

tests/baselines/reference/typesVersions.emptyTypes.types

@@ -0,0 +1,9 @@
+=== /a/ts3.1/index.d.ts ===
+export const a = 0;
+>a : 0
+>0 : 0
+
+=== /b/user.ts ===
+import { a } from "a";
+>a : 0
+

tests/cases/conformance/moduleResolution/typesVersions.emptyTypes.ts

@@ -0,0 +1,18 @@
+// @baseUrl: /
+// @traceResolution: true
+// @target: esnext
+// @module: commonjs
+
+// @filename: /a/package.json
+{
+    "types": "",
+    "typesVersions": {
+        ">=3.1.0-0": { "*" : ["ts3.1/*"] }
+    }
+}
+
+// @filename: /a/ts3.1/index.d.ts
+export const a = 0;
+
+// @filename: /b/user.ts
+import { a } from "a";