From 2ee0b4f7edd32290683e98e231a18ded9595ba6c Mon Sep 17 00:00:00 2001
From: "Mark S. Miller" <erights@gmail.com>
Date: Fri, 10 Nov 2023 17:50:24 -0800
Subject: [PATCH] feat(eventual-send): breakpoint on delivery by env-options

---
 packages/eventual-send/src/local.js           | 58 ++++++++++++++++++-
 packages/pass-style/package.json              |  1 +
 .../pass-style/test/prepare-breakpoints.js    |  6 ++
 .../test/test-breakpoints-on-delivery.js      | 28 +++++++++
 4 files changed, 91 insertions(+), 2 deletions(-)
 create mode 100644 packages/pass-style/test/prepare-breakpoints.js
 create mode 100644 packages/pass-style/test/test-breakpoints-on-delivery.js

diff --git a/packages/eventual-send/src/local.js b/packages/eventual-send/src/local.js
index f7610978ad..63ea6c3b90 100644
--- a/packages/eventual-send/src/local.js
+++ b/packages/eventual-send/src/local.js
@@ -1,6 +1,11 @@
+/* global globalThis */
+import { makeEnvironmentCaptor } from '@endo/env-options';
+
+const { getEnvironmentOption } = makeEnvironmentCaptor(globalThis);
+
 const { details: X, quote: q, Fail } = assert;
 
-const { getOwnPropertyDescriptors, getPrototypeOf, freeze } = Object;
+const { getOwnPropertyDescriptors, getPrototypeOf, freeze, hasOwn } = Object;
 const { apply, ownKeys } = Reflect;
 
 const ntypeof = specimen => (specimen === null ? 'null' : typeof specimen);
@@ -13,6 +18,55 @@ const ntypeof = specimen => (specimen === null ? 'null' : typeof specimen);
  */
 const isObject = val => Object(val) === val;
 
+const BREAKPOINTS = getEnvironmentOption('BREAKPOINTS', '');
+
+/**
+ * @type {Record<string, [string, (number | '*')][]>}
+ */
+// @ts-expect-error doesn't like null __proto__
+const BREAKS = { __proto__: null };
+
+const BP_REGEXP = /(.+?)\.(\w+?|\*)=(\d+?|\*)/;
+
+for (const bp of BREAKPOINTS.split(',')) {
+  if (bp !== '') {
+    const match = BP_REGEXP.exec(bp);
+    if (match === null) {
+      throw Fail`Expected "tagName.methodName=count" ${q(bp)}`;
+    }
+    const [_, tag, verb, countStr] = match;
+    const patts = hasOwn(BREAKS, verb) ? BREAKS[verb] : (BREAKS[verb] = []);
+    patts.push([tag, countStr === '*' ? countStr : +countStr]);
+  }
+}
+
+const debugApply =
+  BREAKPOINTS === ''
+    ? (f, obj, _verb, args) => apply(f, obj, args)
+    : (f, obj, verb, args) => {
+        const patts = BREAKS[verb] || BREAKS['*'];
+        if (patts) {
+          for (const patt of patts) {
+            const [tag, count] = patt;
+            if (tag === '*' || tag === obj[Symbol.toStringTag]) {
+              if (count === '*') {
+                // eslint-disable-next-line no-debugger
+                debugger;
+                break;
+              } else {
+                if (count === 0) {
+                  // eslint-disable-next-line no-debugger
+                  debugger;
+                  break;
+                }
+                patt[1] = count - 1;
+              }
+            }
+          }
+        }
+        return apply(f, obj, args);
+      };
+
 /**
  * Prioritize symbols as earlier than strings.
  *
@@ -96,7 +150,7 @@ export const localApplyMethod = (t, method, args) => {
   const ftype = ntypeof(fn);
   typeof fn === 'function' ||
     Fail`invoked method ${q(method)} is not a function; it is a ${q(ftype)}`;
-  return apply(fn, t, args);
+  return debugApply(fn, t, method, args);
 };
 
 export const localGet = (t, key) => t[key];
diff --git a/packages/pass-style/package.json b/packages/pass-style/package.json
index 60a39fe909..74bf3fff75 100644
--- a/packages/pass-style/package.json
+++ b/packages/pass-style/package.json
@@ -38,6 +38,7 @@
   },
   "devDependencies": {
     "@endo/init": "^0.5.60",
+    "@endo/pass-style": "^0.1.7",
     "@endo/ses-ava": "^0.2.44",
     "ava": "^5.3.0",
     "babel-eslint": "^10.0.3",
diff --git a/packages/pass-style/test/prepare-breakpoints.js b/packages/pass-style/test/prepare-breakpoints.js
new file mode 100644
index 0000000000..dfa1852276
--- /dev/null
+++ b/packages/pass-style/test/prepare-breakpoints.js
@@ -0,0 +1,6 @@
+/* global process */
+
+process.env.BREAKPOINTS = [
+  'Alleged: Bob.foo=*',
+  '*.bar=0',
+].join(',');
diff --git a/packages/pass-style/test/test-breakpoints-on-delivery.js b/packages/pass-style/test/test-breakpoints-on-delivery.js
new file mode 100644
index 0000000000..3fc8905331
--- /dev/null
+++ b/packages/pass-style/test/test-breakpoints-on-delivery.js
@@ -0,0 +1,28 @@
+import './prepare-breakpoints.js';
+import { test } from './prepare-test-env-ava.js';
+
+// eslint-disable-next-line import/order
+import { E } from '@endo/eventual-send';
+import { Far } from '../src/make-far.js';
+
+// Example from test-deep-send.js in @endo/eventual-send
+
+const carol = Far('Carol', {
+  bar: () => console.log('Wut?'),
+});
+
+const bob = Far('Bob', {
+  foo: carolP => E(carolP).bar(),
+});
+
+const alice = Far('Alice', {
+  test: () => E(bob).foo(carol),
+});
+
+// This is not useful as an automated test. Its purpose is to run it under a
+// debugger and see where it breakpoints. To play with it, adjust the
+// settings in prepare-breakpoints.js and try again.
+test('test breakpoints on delivery', async t => {
+  await alice.test();
+  t.pass('introduced');
+});