[Import Maps] Make errors block the whole resolution, Blink-side

Reflects WICG/import-maps#205.

This CL updates tests from #205.

To match the behavior with the updated spec,
this CL turns non-String values into `null` entries
(i.e. make whole resolution fail without further fallback),
instead of ignoring such entries.
Other aspects were already conformant with the updated spec
(i.e. weren't matching with the spec before #205).

This CL updates (test-only) import maps serialization code
so that it matches with the reference implementation, i.e.
dump `null` entries as `null` instead of `[]`.

This CL also updates spec comments.

Bug: 990561, WICG/import-maps#184
Change-Id: Ifa2d04bf20fcef5575c14d135c328730ea09c454

Author: hiroshige-g

import-maps/common/resolving.tentative.html

@@ -15,6 +15,7 @@
   'resources/data-base-url.json',
   'resources/scopes-exact-vs-prefix.json',
   'resources/overlapping-entries.json',
+  'resources/resolving-null.json',
 ]) {
   promise_test(() =>
     runTestsFromJSON(json),

import-maps/common/resources/parsing-addresses-absolute.json

@@ -51,6 +51,8 @@
       "importMapBaseURL": "https://base.example/path1/path2/path3",
       "expectedParsedImportMap": {
         "imports": {
+          "unparseable2": null,
+          "unparseable3": null,
           "invalidButParseable1": "https://example.org/",
           "invalidButParseable2": "https://example.com///",
           "prettyNormal": "https://example.net/",

import-maps/common/resources/parsing-addresses-invalid.json

@@ -13,7 +13,13 @@
       },
       "importMapBaseURL": "https://base.example/path1/path2/path3",
       "expectedParsedImportMap": {
-        "imports": {},
+        "imports": {
+          "foo1": null,
+          "foo2": null,
+          "foo3": null,
+          "foo4": null,
+          "foo5": null
+        },
         "scopes": {}
       }
     }

import-maps/common/resources/parsing-addresses.json

@@ -29,7 +29,11 @@
       },
       "importMapBaseURL": "data:text/html,test",
       "expectedParsedImportMap": {
-        "imports": {},
+        "imports": {
+          "dotSlash": null,
+          "dotDotSlash": null,
+          "slash": null
+        },
         "scopes": {}
       }
     },
@@ -65,7 +69,15 @@
       },
       "importMapBaseURL": "https://base.example/path1/path2/path3",
       "expectedParsedImportMap": {
-        "imports": {},
+        "imports": {
+          "dotSlash1": null,
+          "dotDotSlash1": null,
+          "dotSlash2": null,
+          "dotDotSlash2": null,
+          "slash2": null,
+          "dotSlash3": null,
+          "dotDotSlash3": null
+        },
         "scopes": {}
       }
     }

import-maps/common/resources/parsing-schema-specifier-map.json

@@ -18,6 +18,12 @@
       },
       "expectedParsedImportMap": {
         "imports": {
+          "null": null,
+          "boolean": null,
+          "number": null,
+          "object": null,
+          "array": null,
+          "array2": null,
           "string": "https://example.com/"
         },
         "scopes": {}

import-maps/common/resources/parsing-trailing-slashes.json

@@ -7,7 +7,9 @@
   },
   "importMapBaseURL": "https://base.example/path1/path2/path3",
   "expectedParsedImportMap": {
-    "imports": {},
+    "imports": {
+      "trailer/": null
+    },
     "scopes": {}
   }
 }

import-maps/common/resources/resolving-null.json

@@ -0,0 +1,82 @@
+{
+  "importMapBaseURL": "https://example.com/app/index.html",
+  "baseURL": "https://example.com/js/app.mjs",
+  "name": "Entries with errors shouldn't allow fallback",
+  "tests": {
+    "No fallback to less-specific prefixes": {
+      "importMap": {
+        "imports": {
+          "null/": "/1/",
+          "null/b/": null,
+          "null/b/c/": "/1/2/",
+          "invalid-url/": "/1/",
+          "invalid-url/b/": "https://:invalid-url:/",
+          "invalid-url/b/c/": "/1/2/",
+          "without-trailing-slashes/": "/1/",
+          "without-trailing-slashes/b/": "/x",
+          "without-trailing-slashes/b/c/": "/1/2/",
+          "prefix-resolution-error/": "/1/",
+          "prefix-resolution-error/b/": "data:text/javascript,/",
+          "prefix-resolution-error/b/c/": "/1/2/"
+        }
+      },
+      "expectedResults": {
+        "null/x": "https://example.com/1/x",
+        "null/b/x": null,
+        "null/b/c/x": "https://example.com/1/2/x",
+        "invalid-url/x": "https://example.com/1/x",
+        "invalid-url/b/x": null,
+        "invalid-url/b/c/x": "https://example.com/1/2/x",
+        "without-trailing-slashes/x": "https://example.com/1/x",
+        "without-trailing-slashes/b/x": null,
+        "without-trailing-slashes/b/c/x": "https://example.com/1/2/x",
+        "prefix-resolution-error/x": "https://example.com/1/x",
+        "prefix-resolution-error/b/x": null,
+        "prefix-resolution-error/b/c/x": "https://example.com/1/2/x"
+      }
+    },
+    "No fallback to less-specific scopes": {
+      "importMap": {
+        "imports": {
+          "null": "https://example.com/a",
+          "invalid-url": "https://example.com/b",
+          "without-trailing-slashes/": "https://example.com/c/",
+          "prefix-resolution-error/": "https://example.com/d/"
+        },
+        "scopes": {
+          "/js/": {
+            "null": null,
+            "invalid-url": "https://:invalid-url:/",
+            "without-trailing-slashes/": "/x",
+            "prefix-resolution-error/": "data:text/javascript,/"
+          }
+        }
+      },
+      "expectedResults": {
+        "null": null,
+        "invalid-url": null,
+        "without-trailing-slashes/x": null,
+        "prefix-resolution-error/x": null
+      }
+    },
+    "No fallback to absolute URL parsing": {
+      "importMap": {
+        "imports": {},
+        "scopes": {
+          "/js/": {
+            "https://example.com/null": null,
+            "https://example.com/invalid-url": "https://:invalid-url:/",
+            "https://example.com/without-trailing-slashes/": "/x",
+            "https://example.com/prefix-resolution-error/": "data:text/javascript,/"
+          }
+        }
+      },
+      "expectedResults": {
+        "https://example.com/null": null,
+        "https://example.com/invalid-url": null,
+        "https://example.com/without-trailing-slashes/x": null,
+        "https://example.com/prefix-resolution-error/x": null
+      }
+    }
+  }
+}