From 3dc3772bb0c05c3106b2a5b84116aeb033f7e106 Mon Sep 17 00:00:00 2001
From: Myles Borins <mylesborins@google.com>
Date: Fri, 17 Apr 2020 17:13:16 -0400
Subject: [PATCH] module: improve error for invalid package targets

For targets that are strings that do not start with `./` or `/` the
error will now have additional information about what the programming
error is.

Closes: https://github.com/nodejs/node/issues/32034

PR-URL: https://github.com/nodejs/node/pull/32052
Fixes: https://github.com/nodejs/node/issues/32034
Reviewed-By: Geoffrey Booth <webmaster@geoffreybooth.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Jan Krems <jan.krems@gmail.com>
Reviewed-By: Guy Bedford <guybedford@gmail.com>
Signed-off-by: Myles Borins <myles.borins@gmail.com>
---
 lib/internal/errors.js                          | 17 ++++++++++++++---
 test/es-module/test-esm-exports.mjs             |  4 ++++
 .../node_modules/pkgexports/package.json        |  1 +
 3 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/lib/internal/errors.js b/lib/internal/errors.js
index 94088aac108843..363810e7a71a36 100644
--- a/lib/internal/errors.js
+++ b/lib/internal/errors.js
@@ -20,6 +20,7 @@ const {
   ObjectDefineProperty,
   ObjectKeys,
   StringPrototypeSlice,
+  StringPrototypeStartsWith,
   Symbol,
   SymbolFor,
   WeakMap,
@@ -1096,18 +1097,28 @@ E('ERR_INVALID_PACKAGE_CONFIG', (path, message, hasMessage = true) => {
 }, Error);
 E('ERR_INVALID_PACKAGE_TARGET',
   (pkgPath, key, subpath, target, base = undefined) => {
+    const relError = typeof target === 'string' &&
+      target.length && !StringPrototypeStartsWith(target, './');
     if (key === null) {
       if (subpath !== '') {
         return `Invalid "exports" target ${JSONStringify(target)} defined ` +
         `for '${subpath}' in the package config ${pkgPath} imported from ` +
-        base;
+        `${base}.${relError ? '; targets must start with "./"' : ''}`;
       } else {
         return `Invalid "exports" main target ${target} defined in the ` +
-          `package config ${pkgPath} imported from ${base}.`;
+          `package config ${pkgPath} imported from ${base}${relError ?
+            '; targets must start with "./"' : ''}`;
       }
     } else if (key === '.') {
       return `Invalid "exports" main target ${JSONStringify(target)} defined ` +
-      `in the package config ${pkgPath}${sep}package.json`;
+      `in the package config ${pkgPath}${sep}package.json${relError ?
+        '; targets must start with "./"' : ''}`;
+    } else if (typeof target === 'string' && target !== '' &&
+      !StringPrototypeStartsWith(target, './')) {
+      return `Invalid "exports" target ${JSONStringify(target)} defined for '${
+        StringPrototypeSlice(key, 0, -subpath.length || key.length)}' in the ` +
+        `package config ${pkgPath}${sep}package.json; ` +
+        'targets must start with "./"';
     } else {
       return `Invalid "exports" target ${JSONStringify(target)} defined for '${
         StringPrototypeSlice(key, 0, -subpath.length || key.length)}' in the ` +
diff --git a/test/es-module/test-esm-exports.mjs b/test/es-module/test-esm-exports.mjs
index 0b47df3f6a2354..5ed718b131e71e 100644
--- a/test/es-module/test-esm-exports.mjs
+++ b/test/es-module/test-esm-exports.mjs
@@ -79,6 +79,7 @@ import fromInside from '../fixtures/node_modules/pkgexports/lib/hole.js';
     ['pkgexports/null', './null'],
     ['pkgexports/invalid2', './invalid2'],
     ['pkgexports/invalid3', './invalid3'],
+    ['pkgexports/invalid5', 'invalid5'],
     // Missing / invalid fallbacks
     ['pkgexports/nofallback1', './nofallback1'],
     ['pkgexports/nofallback2', './nofallback2'],
@@ -107,6 +108,9 @@ import fromInside from '../fixtures/node_modules/pkgexports/lib/hole.js';
       strictEqual(err.code, 'ERR_INVALID_PACKAGE_TARGET');
       assertStartsWith(err.message, 'Invalid "exports"');
       assertIncludes(err.message, subpath);
+      if (!subpath.startsWith('./')) {
+        assertIncludes(err.message, 'targets must start with');
+      }
     }));
   }
 
diff --git a/test/fixtures/node_modules/pkgexports/package.json b/test/fixtures/node_modules/pkgexports/package.json
index f3ec20c49b2b91..43ccf7795b978e 100644
--- a/test/fixtures/node_modules/pkgexports/package.json
+++ b/test/fixtures/node_modules/pkgexports/package.json
@@ -13,6 +13,7 @@
     "./invalid2": 1234,
     "./invalid3": "",
     "./invalid4": {},
+    "./invalid5": "invalid5.js",
     "./fallbackdir/": [[], null, {}, "builtin:x/", "./fallbackfile", "./"],
     "./fallbackfile": [[], null, {}, "builtin:x", "./asdf.js"],
     "./nofallback1": [],