feat(endo): Improve JSON file parse error messages

packages/endo/src/archive.js

@@ -6,6 +6,7 @@ import { parseExtension } from "./extension.js";
 import { compartmentMapForNodeModules } from "./compartmap.js";
 import { search } from "./search.js";
 import { assemble } from "./assemble.js";
+import * as json from "./json.js";
 
 const { entries, freeze, fromEntries, values } = Object;
 
@@ -165,10 +166,14 @@ export const makeArchive = async (read, moduleLocation) => {
   const {
     packageLocation,
     packageDescriptorText,
+    packageDescriptorLocation,
     moduleSpecifier
   } = await search(read, moduleLocation);
 
-  const packageDescriptor = JSON.parse(packageDescriptorText);
+  const packageDescriptor = json.parse(
+    packageDescriptorText,
+    packageDescriptorLocation
+  );
   const compartmentMap = await compartmentMapForNodeModules(
     read,
     packageLocation,

packages/endo/src/compartmap.js

@@ -1,6 +1,7 @@
 /* eslint no-shadow: 0 */
 
 import { inferExports } from "./infer-exports.js";
+import * as json from "./json.js";
 
 const { create, entries, keys, values } = Object;
 
@@ -9,7 +10,7 @@ const decoder = new TextDecoder();
 // q, as in quote, for enquoting strings in error messages.
 const q = JSON.stringify;
 
-const resolve = (rel, abs) => new URL(rel, abs).toString();
+const resolveLocation = (rel, abs) => new URL(rel, abs).toString();
 
 const basename = location => {
   const { pathname } = new URL(location);
@@ -21,13 +22,15 @@ const basename = location => {
 };
 
 const readDescriptor = async (read, packageLocation) => {
-  const descriptorPath = resolve("package.json", packageLocation);
-  const descriptorBytes = await read(descriptorPath).catch(_error => undefined);
+  const descriptorLocation = resolveLocation("package.json", packageLocation);
+  const descriptorBytes = await read(descriptorLocation).catch(
+    _error => undefined
+  );
   if (descriptorBytes === undefined) {
     return undefined;
   }
   const descriptorText = decoder.decode(descriptorBytes);
-  const descriptor = JSON.parse(descriptorText);
+  const descriptor = json.parse(descriptorText, descriptorLocation);
   return descriptor;
 };
 
@@ -49,22 +52,22 @@ const readDescriptorWithMemo = async (memo, read, packageLocation) => {
 // find it efficiently.
 const findPackage = async (readDescriptor, directory, name) => {
   for (;;) {
-    const packageLocation = resolve(`node_modules/${name}/`, directory);
+    const packageLocation = resolveLocation(`node_modules/${name}/`, directory);
     // eslint-disable-next-line no-await-in-loop
     const packageDescriptor = await readDescriptor(packageLocation);
     if (packageDescriptor !== undefined) {
       return { packageLocation, packageDescriptor };
     }
 
-    const parent = resolve("../", directory);
+    const parent = resolveLocation("../", directory);
     if (parent === directory) {
       return undefined;
     }
     directory = parent;
 
     const base = basename(directory);
     if (base === "node_modules") {
-      directory = resolve("../", directory);
+      directory = resolveLocation("../", directory);
       if (parent === directory) {
         return undefined;
       }

packages/endo/src/import-archive.js

@@ -3,6 +3,7 @@
 import { readZip } from "./zip.js";
 import { assemble } from "./assemble.js";
 import { parserForLanguage } from "./parse.js";
+import * as json from "./json.js";
 
 const decoder = new TextDecoder();
 
@@ -35,7 +36,7 @@ export const parseArchive = async (archiveBytes, archiveLocation) => {
 
   const compartmentMapBytes = await archive.read("compartmap.json");
   const compartmentMapText = decoder.decode(compartmentMapBytes);
-  const compartmentMap = JSON.parse(compartmentMapText);
+  const compartmentMap = json.parse(compartmentMapText, "compartmap.json");
 
   const execute = (endowments, modules) => {
     const { compartments, entry: moduleSpecifier } = compartmentMap;

packages/endo/src/import.js

@@ -4,6 +4,7 @@ import { compartmentMapForNodeModules } from "./compartmap.js";
 import { search } from "./search.js";
 import { assemble } from "./assemble.js";
 import { parseExtension } from "./extension.js";
+import * as json from "./json.js";
 
 const decoder = new TextDecoder();
 
@@ -72,10 +73,14 @@ export const loadLocation = async (read, moduleLocation) => {
   const {
     packageLocation,
     packageDescriptorText,
+    packageDescriptorLocation,
     moduleSpecifier
   } = await search(read, moduleLocation);
 
-  const packageDescriptor = JSON.parse(packageDescriptorText);
+  const packageDescriptor = json.parse(
+    packageDescriptorText,
+    packageDescriptorLocation
+  );
   const compartmentMap = await compartmentMapForNodeModules(
     read,
     packageLocation,

packages/endo/src/json.js

@@ -0,0 +1,7 @@
+export const parse = (source, location) => {
+  try {
+    return JSON.parse(source);
+  } catch (error) {
+    throw new SyntaxError(`Cannot parse JSON from ${location}, ${error}`);
+  }
+};

packages/endo/src/parse.js

@@ -2,6 +2,7 @@
 
 import { parseRequires } from "./parse-requires.js";
 import { parseExtension } from "./extension.js";
+import * as json from "./json.js";
 
 const { entries, freeze, fromEntries } = Object;
 
@@ -73,13 +74,7 @@ export const parseCjs = (source, _specifier, location, packageLocation) => {
 export const parseJson = (source, _specifier, location, _packageLocation) => {
   const imports = freeze([]);
   const execute = exports => {
-    try {
-      exports.default = JSON.parse(source);
-    } catch (error) {
-      throw new SyntaxError(
-        `Cannot parse JSON module at ${location}, ${error}`
-      );
-    }
+    exports.default = json.parse(source, location);
   };
   return {
     parser: "json",

packages/endo/src/search.js

@@ -29,6 +29,7 @@ export const search = async (read, moduleLocation) => {
       return {
         packageLocation: directory,
         packageDescriptorText,
+        packageDescriptorLocation,
         moduleSpecifier: relativize(relative(directory, moduleLocation))
       };
     }