Only apply /-prefix handling to special URL-like specifiers

Closes #166.

README.md

@@ -219,6 +219,8 @@ This version ensures that import statements for specifiers that start with the s
 
 In general, the point is that the remapping works the same for URL-like imports as for bare imports. Our previous examples changed the resolution of specifiers like `"lodash"`, and thus changed the meaning of `import "lodash"`. Here we're changing the resolution of specifiers like `"/app/helpers.mjs"`, and thus changing the meaning of `import "/app/helpers.mjs"`.
 
+Note that this trailing-slash variant of URL-like specifier mapping only works if the URL-like specifier has a [special scheme](https://url.spec.whatwg.org/#special-scheme): e.g., a mapping of `"data:text/": "/foo"` will not impact the meaning of `import "data:text/javascript,console.log('test')"`, but instead will only impact `import "data:text/"`.
+
 #### Mapping away hashes in script filenames
 
 Script files are often given a unique hash in their filename, to improve cachability. See [this general discussion of the technique](https://jakearchibald.com/2016/caching-best-practices/), or [this more JavaScript- and webpack-focused discussion](https://developers.google.com/web/fundamentals/performance/webpack/use-long-term-caching).

reference-implementation/__tests__/json/url-specifiers.json

@@ -9,7 +9,14 @@
       "/test/": "/lib/url-trailing-slash/",
       "./test/": "/lib/url-trailing-slash-dot/",
       "/test": "/lib/test1.mjs",
-      "../test": "/lib/test2.mjs"
+      "../test": "/lib/test2.mjs",
+      "data:text/": "/lib/test-data/",
+      "about:text/": "/lib/test-about/",
+      "blob:text/": "/lib/test-blob/",
+      "blah:text/": "/lib/test-blah/",
+      "file:text/": "/lib/test-file/",
+      "ftp:text/": "/lib/test-ftp/",
+      "ws:text/": "/lib/test-ws/"
     }
   },
   "importMapBaseURL": "https://example.com/app/index.html",
@@ -47,6 +54,24 @@
       "expectedResults": {
         "/test": "https://example.com/lib/test2.mjs"
       }
+    },
+    "Non-special vs. special schemes": {
+      "expectedResults": {
+        "data:text/javascript,console.log('foo')": "data:text/javascript,console.log('foo')",
+        "data:text/": "https://example.com/lib/test-data/",
+        "about:text/foo": "about:text/foo",
+        "about:text/": "https://example.com/lib/test-about/",
+        "blob:text/foo": "blob:text/foo",
+        "blob:text/": "https://example.com/lib/test-blob/",
+        "blah:text/foo": "blah:text/foo",
+        "blah:text/": "https://example.com/lib/test-blah/",
+        "ftp:text/foo": "https://example.com/lib/test-ftp/foo",
+        "ftp:text/": "https://example.com/lib/test-ftp/",
+        "file:text/foo": "https://example.com/lib/test-file/foo",
+        "file:text/": "https://example.com/lib/test-file/",
+        "ws:text/foo": "https://example.com/lib/test-ws/foo",
+        "ws:text/": "https://example.com/lib/test-ws/"
+      }
     }
   }
 }

reference-implementation/lib/resolver.js

@@ -1,6 +1,6 @@
 'use strict';
 const assert = require('assert');
-const { tryURLLikeSpecifierParse, tryURLParse } = require('./utils.js');
+const { tryURLLikeSpecifierParse, tryURLParse, isSpecial } = require('./utils.js');
 
 exports.resolve = (specifier, parsedImportMap, scriptURL) => {
   const asURL = tryURLLikeSpecifierParse(specifier, scriptURL);
@@ -10,14 +10,14 @@ exports.resolve = (specifier, parsedImportMap, scriptURL) => {
   for (const [scopePrefix, scopeImports] of Object.entries(parsedImportMap.scopes)) {
     if (scopePrefix === scriptURLString ||
         (scopePrefix.endsWith('/') && scriptURLString.startsWith(scopePrefix))) {
-      const scopeImportsMatch = resolveImportsMatch(normalizedSpecifier, scopeImports);
+      const scopeImportsMatch = resolveImportsMatch(normalizedSpecifier, asURL, scopeImports);
       if (scopeImportsMatch !== null) {
         return scopeImportsMatch;
       }
     }
   }
 
-  const topLevelImportsMatch = resolveImportsMatch(normalizedSpecifier, parsedImportMap.imports);
+  const topLevelImportsMatch = resolveImportsMatch(normalizedSpecifier, asURL, parsedImportMap.imports);
   if (topLevelImportsMatch !== null) {
     return topLevelImportsMatch;
   }
@@ -30,7 +30,7 @@ exports.resolve = (specifier, parsedImportMap, scriptURL) => {
   throw new TypeError(`Unmapped bare specifier "${specifier}"`);
 };
 
-function resolveImportsMatch(normalizedSpecifier, specifierMap) {
+function resolveImportsMatch(normalizedSpecifier, asURL, specifierMap) {
   for (const [specifierKey, resolutionResult] of Object.entries(specifierMap)) {
     // Exact-match case
     if (specifierKey === normalizedSpecifier) {
@@ -44,7 +44,9 @@ function resolveImportsMatch(normalizedSpecifier, specifierMap) {
     }
 
     // Package prefix-match case
-    if (specifierKey.endsWith('/') && normalizedSpecifier.startsWith(specifierKey)) {
+    if (specifierKey.endsWith('/') &&
+        normalizedSpecifier.startsWith(specifierKey) &&
+        (!asURL || isSpecial(asURL))) {
       if (resolutionResult === null) {
         throw new TypeError(`Blocked by a null entry for "${specifierKey}"`);
       }

reference-implementation/lib/utils.js

@@ -17,3 +17,7 @@ exports.tryURLLikeSpecifierParse = (specifier, baseURL) => {
   const url = exports.tryURLParse(specifier);
   return url;
 };
+
+// https://url.spec.whatwg.org/#special-scheme
+const specialProtocols = new Set(["ftp:", "file:", "http:", "https:", "ws:", "wss:"]);
+exports.isSpecial = url => specialProtocols.has(url.protocol);

spec.bs

@@ -398,25 +398,31 @@ To <dfn>register an import map</dfn> given an {{HTMLScriptElement}} |element|:
   1. Let |normalizedSpecifier| be the [=URL serializer|serialization=] of |asURL|, if |asURL| is non-null; otherwise, |specifier|.
   1. [=map/For each=] |scopePrefix| → |scopeImports| of |importMap|'s [=import map/scopes=],
     1. If |scopePrefix| is |baseURLString|, or if |scopePrefix| ends with U+002F (/) and |baseURLString| [=string/starts with=] |scopePrefix|, then:
-      1. Let |scopeImportsMatch| be the result of [=resolving an imports match=] given |normalizedSpecifier| and |scopeImports|.
+      1. Let |scopeImportsMatch| be the result of [=resolving an imports match=] given |normalizedSpecifier|, |asURL|, and |scopeImports|.
       1. If |scopeImportsMatch| is not null, then return |scopeImportsMatch|.
-  1. Let |topLevelImportsMatch| be the result of [=resolving an imports match=] given |normalizedSpecifier| and |importMap|'s [=import map/imports=].
+  1. Let |topLevelImportsMatch| be the result of [=resolving an imports match=] given |normalizedSpecifier|, |asURL|, and |importMap|'s [=import map/imports=].
   1. If |topLevelImportsMatch| is not null, then return |topLevelImportsMatch|.
   1. <p class="note">At this point, the specifier was able to be turned in to a URL, but it wasn't remapped to anything by |importMap|.</p>
     If |asURL| is not null, then return |asURL|.
   1. Throw a {{TypeError}} indicating that |specifier| was a bare specifier, but was not remapped to anything by |importMap|.
 </div>
 
 <div algorithm>
-  To <dfn lt="resolve an imports match|resolving an imports match">resolve an imports match</dfn>, given a [=string=] |normalizedSpecifier| and a [=specifier map=] |specifierMap|:
+  To <dfn lt="resolve an imports match|resolving an imports match">resolve an imports match</dfn>, given a [=string=] |normalizedSpecifier|, a [=URL=] or null |asURL|, and a [=specifier map=] |specifierMap|:
 
   1. For each |specifierKey| → |resolutionResult| of |specifierMap|,
     1. If |specifierKey| is |normalizedSpecifier|, then:
       1. If |resolutionResult| is null, then throw a {{TypeError}} indicating that resolution of |specifierKey| was blocked by a null entry.
         <p class="note">This will terminate the entire [=resolve a module specifier=] algorithm, without any further fallbacks.</p>
       1. Assert: |resolutionResult| is a [=URL=].
       1. Return |resolutionResult|.
-    1. If |specifierKey| ends with U+002F (/) and |normalizedSpecifier| [=string/starts with=] |specifierKey|, then:
+    1. If all of the following are true:
+
+      * |specifierKey| ends with U+002F (/),
+      * |normalizedSpecifier| [=string/starts with=] |specifierKey|, and
+      * either |asURL| is null, or |asURL| [=is special=]
+
+      then:
       1. If |resolutionResult| is null, then throw a {{TypeError}} indicating that resolution of |specifierKey| was blocked by a null entry.
         <p class="note">This will terminate the entire [=resolve a module specifier=] algorithm, without any further fallbacks.</p>
       1. Assert: |resolutionResult| is a [=URL=].