build: add ESLint to script/lint and containerize linting (closes #152)

eslint.config.js

@@ -0,0 +1,152 @@
+// ESLint flat config. Static analysis for make check; formatting stays with
+// prettier (script/fmt-check), so nothing here touches style.
+//
+// The sources are CommonJS and are bundled per entrypoint by build.js, so the
+// globals differ by tree and are declared per tree below. Getting that wrong in
+// either direction defeats the point: too few globals buries a real no-undef in
+// false positives, too many hides the next unimported identifier.
+
+const js = require("@eslint/js");
+const globals = require("globals");
+
+// The extension APIs. MV3 Chrome exposes `chrome`; Firefox exposes both, and
+// the code feature-detects between them.
+const extensionGlobals = {
+    chrome: "readonly",
+    browser: "readonly",
+};
+
+const commonjs = {
+    ecmaVersion: 2024,
+    sourceType: "commonjs",
+};
+
+module.exports = [
+    {
+        ignores: ["dist/", "node_modules/"],
+    },
+
+    js.configs.recommended,
+
+    {
+        rules: {
+            // The two rules this config exists for. Both are already
+            // error-level in the recommended set; restated so a future
+            // recommended-set change cannot silently downgrade them.
+            "no-undef": "error",
+            // `_`-prefixed arguments are the deliberate "present for the
+            // interface, unused here" marker: the popup views share one
+            // init(ctx) signature and three of the eight do not read ctx.
+            // An unused catch binding is written `catch {`, which the repo
+            // already does, so caught errors stay checked.
+            "no-unused-vars": ["error", { argsIgnorePattern: "^_" }],
+
+            // Off tree-wide: it requires every rethrow to carry `{ cause }`,
+            // at 3 sites today (src/shared/balances.js 207 and 215,
+            // tests/e2e/firefox/run.js 131). That is a change to what the
+            // wallet's error paths actually throw, and it is a decision of its
+            // own rather than a side effect of turning a linter on — so it is
+            // off everywhere, including for new code, until that decision is
+            // made. Unlike no-useless-assignment below, this is not an
+            // accommodation of particular sites and must not be scoped to
+            // them.
+            "preserve-caught-error": "off",
+        },
+    },
+
+    // no-useless-assignment stays on everywhere except the two files that
+    // wipe decrypted key material: the `password = null` and
+    // `decryptedSecret = null` assignments after use are dead by construction
+    // — that is what a best-effort wipe is — and the rule's fix is to delete
+    // the wipe. 9 sites: approval.js 582, 593, 618, 648, 692, 703, 728, 764
+    // and confirmTx.js 459. Everything else in the tree is still checked, so
+    // an ordinary dead store elsewhere is still an error.
+    {
+        files: ["src/popup/views/approval.js", "src/popup/views/confirmTx.js"],
+        rules: {
+            "no-useless-assignment": "off",
+        },
+    },
+
+    // Popup and content scripts: page/window context.
+    {
+        files: ["src/popup/**/*.js", "src/content/**/*.js"],
+        languageOptions: {
+            ...commonjs,
+            globals: { ...globals.browser, ...extensionGlobals },
+        },
+    },
+
+    // MV3 background: a service worker, with no window and no document.
+    {
+        files: ["src/background/**/*.js"],
+        languageOptions: {
+            ...commonjs,
+            globals: { ...globals.serviceworker, ...extensionGlobals },
+        },
+    },
+
+    // src/shared is bundled into both, so it may only use what both provide:
+    // the service worker globals are the intersection, plus the extension APIs.
+    {
+        files: ["src/shared/**/*.js"],
+        languageOptions: {
+            ...commonjs,
+            globals: { ...globals.serviceworker, ...extensionGlobals },
+        },
+    },
+
+    // src/shared/ens.js is the documented exception to the line above: its own
+    // header says POPUP ONLY, it caches in localStorage, and only popup views
+    // require it. Linting it as a service worker would be wrong about the file.
+    {
+        files: ["src/shared/ens.js"],
+        languageOptions: {
+            ...commonjs,
+            globals: { ...globals.browser, ...extensionGlobals },
+        },
+    },
+
+    // Unit tests: jest on node.
+    {
+        files: ["tests/**/*.test.js"],
+        languageOptions: {
+            ...commonjs,
+            globals: { ...globals.node, ...globals.jest },
+        },
+    },
+
+    // The build script is a plain node program.
+    {
+        files: ["build.js"],
+        languageOptions: {
+            ...commonjs,
+            globals: { ...globals.node },
+        },
+    },
+
+    // The e2e harnesses are node programs that also carry, inline, the
+    // callbacks they ship into the browser via page.evaluate — so both
+    // contexts really are present in the same file and both sets of globals
+    // are in scope somewhere in it.
+    {
+        files: ["tests/e2e/**/*.js"],
+        languageOptions: {
+            ...commonjs,
+            globals: {
+                ...globals.node,
+                ...globals.browser,
+                ...extensionGlobals,
+            },
+        },
+    },
+
+    // This config file itself.
+    {
+        files: ["eslint.config.js"],
+        languageOptions: {
+            ...commonjs,
+            globals: { ...globals.node },
+        },
+    },
+];