Add babel plugin that removes code from @glimmer/debug that terser co…

…uldn't figure out -- I also left some notes about the problem that terser is running in to -- it seems to be related to indirection of identity functions that 'passes' isn't smart enough to figure out

We get big wins (side-wise) from sideEffects: false, but things break.

This babel plugin is feeling more and more brittle, the more we want to
strip.

packages/@glimmer-workspace/build/lib/config.js

@@ -1,6 +1,7 @@
 /* eslint-disable no-console */
 // @ts-check
 import { existsSync, readFileSync } from 'node:fs';
+import { createRequire } from 'node:module';
 import { dirname, resolve } from 'node:path';
 import { fileURLToPath } from 'node:url';
 
@@ -12,6 +13,8 @@ import ts from 'typescript';
 
 import inline from './inline.js';
 
+const require = createRequire(import.meta.url);
+
 // eslint-disable-next-line import/no-named-as-default-member
 const { ModuleKind, ModuleResolutionKind, ScriptTarget, ImportsNotUsedAsValues } = ts;
 
@@ -94,7 +97,7 @@ export function typescript(pkg, config) {
   return rollupTS({
     transpiler: 'babel',
     transpileOnly: true,
-    babelConfig: { presets },
+    babelConfig: { presets, plugins: [require.resolve('@glimmer/local-debug-babel-plugin')] },
     /**
      * This shouldn't be required, but it is.
      * If we use @rollup/plugin-babel, we can remove this.
@@ -452,10 +455,15 @@ export class Package {
 
       return {
         input: resolve(root, ts),
+        treeshake: {
+          // moduleSideEffects: false,
+          moduleSideEffects: (id, external) => !external,
+        },
         output: {
           file: resolve(root, 'dist', env, file),
           format,
           sourcemap: true,
+          hoistTransitiveImports: false,
           exports: format === 'cjs' ? 'named' : 'auto',
         },
         onwarn: (warning, warn) => {

packages/@glimmer-workspace/build/package.json

@@ -13,6 +13,7 @@
     "test:types": "tsc --noEmit -p ../tsconfig.json"
   },
   "dependencies": {
+    "@glimmer/local-debug-babel-plugin": "workspace:*",
     "@rollup/plugin-commonjs": "^25.0.7",
     "@rollup/plugin-node-resolve": "^15.2.3",
     "@rollup/plugin-replace": "^5.0.5",

packages/@glimmer/local-debug-babel-plugin/index.js

@@ -0,0 +1,110 @@
+/**
+ * https://astexplorer.net/#/gist/c3f41b75af73006f64476775e73f7daa/e6e3e120df8404b1bff308bec3ed89eaaf0b05f2
+ *
+ * This plugin exists because, _even when we inline @glimmer/debug_,
+ * we cannot get terser to remove/inline/unwrap identity functions.
+ *
+ * Repro here: https://try.terser.org/
+ *
+ * ```js
+    function x(x) { return x; }
+    function y(x, y, z) { return x; };
+
+    function abc(a) { return x(a); }
+    function abc2(a) { return y(a); }
+
+    export function example() {
+      return `${x(2)} ${y("2")} ${abc(3)} ${abc2("3")}`;
+    }
+  ```
+
+  With Options:
+
+  {
+    module: true,
+    compress: {
+      passes: 6,
+      module: true,
+      inline: 3, // default
+    },
+    mangle: {},
+    output: {},
+    parse: {},
+    rename: {},
+  }
+ */
+export default function (babel) {
+  let _removeCheck = removeChecks(babel);
+
+  return {
+    name: 'Cleanup local-debug code that terser could not',
+    visitor: {
+      ImportDeclaration(path, state) {
+        _removeCheck.ImportDeclaration(path, state);
+      },
+      CallExpression(path, state) {
+        _removeCheck.CallExpression(path, state);
+      },
+    },
+  };
+}
+
+function removeChecks({ template }) {
+  let stateKey = Symbol.for('removeChecks');
+
+  const unwrap = ['check'];
+  const trueFn = ['CheckInterface', 'wrap', 'CheckOr', 'CheckFunction', 'CheckObject'];
+  const removeEntirely = ['recordStackSize'];
+
+  function isToBeRemoved(callPath, state) {
+    if (!state) return;
+
+    let ourState = state[stateKey];
+
+    if (!ourState) return;
+    /**
+     * Do we want to support local aliasing / re-assignment?
+     * if so, this would break
+     */
+    if (!ourState?.names?.has(callPath.node.callee.name)) return;
+
+    return true;
+  }
+
+  return {
+    ImportDeclaration(path, state) {
+      let node = path.node;
+
+      if (!node.source) return;
+      if (node.source.value !== '@glimmer/debug') return;
+
+      state[stateKey] ??= { names: new Set(), nodes: [] };
+
+      node.specifiers.forEach((specifier) => {
+        let name = specifier.local.name;
+        let relevant =
+          unwrap.includes(name) || removeEntirely.includes(name) || trueFn.includes(name);
+        if (!relevant) return;
+
+        state[stateKey].names.add(name);
+        state[stateKey].nodes.push(specifier.local);
+      });
+    },
+    CallExpression(path, state) {
+      if (isToBeRemoved(path, state)) {
+        let name = path.node.callee.name;
+        if (removeEntirely.includes(name)) {
+          path.remove();
+          return;
+        }
+
+        if (trueFn.includes(name)) {
+          path.replaceWith(template(`() => true`)());
+          return;
+        }
+
+        path.replaceWith(path.node.arguments[0]);
+      }
+    },
+  };
+}

packages/@glimmer/local-debug-babel-plugin/package.json

@@ -0,0 +1,13 @@
+{
+  "name": "@glimmer/local-debug-babel-plugin",
+  "version": "0.92.0",
+  "license": "MIT",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/glimmerjs/glimmer-vm.git",
+    "directory": "packages/@glimmer/local-debug-babel-plugin"
+  },
+  "type": "module",
+  "private": true,
+  "main": "index.js"
+}