Refactor CompilerError

This commit repurposes CompilerError to represent an aggregate of error details 
accumulated during HIR lowering. It also fixes the playground to correctly 
render errors again.

compiler/forget/packages/playground/components/Editor/Output.tsx

@@ -146,8 +146,12 @@ function Output({ store }: Props) {
   const compilerOutput = useMemo(() => compile(store.source), [store.source]);
 
   if (typeof compilerOutput === "string") {
-    if (compilerOutput === "") return <div></div>;
-    return <div>error: ${compilerOutput}</div>;
+    if (compilerOutput === "") return <></>;
+    return (
+      <pre>
+        <code>${compilerOutput}</code>
+      </pre>
+    );
   }
 
   return (

compiler/forget/src/CompilerError.ts

@@ -1,5 +1,4 @@
 import { Node, NodePath } from "@babel/core";
-import type { ExtractClassProperties } from "./Utils/types";
 import { assertExhaustive } from "./Utils/utils";
 
 export enum ErrorSeverity {
@@ -7,9 +6,24 @@ export enum ErrorSeverity {
   Todo = "Todo",
 }
 
-export type CompilerErrorOptions = ExtractClassProperties<CompilerError>;
+export type CompilerErrorOptions = {
+  reason: string;
+  severity: ErrorSeverity;
+  nodePath: AnyNodePath | null;
+};
 type AnyNodePath = NodePath<Node | null | undefined>;
+type CompilerErrorKind = typeof InvalidInputError | typeof TodoError;
 
+function mapSeverityToErrorCtor(severity: ErrorSeverity): CompilerErrorKind {
+  switch (severity) {
+    case ErrorSeverity.InvalidInput:
+      return InvalidInputError;
+    case ErrorSeverity.Todo:
+      return TodoError;
+    default:
+      assertExhaustive(severity, `Unhandled severity level: ${severity}`);
+  }
+}
 class InvalidInputError extends Error {
   constructor(message: string) {
     super(message);
@@ -23,30 +37,13 @@ class TodoError extends Error {
   }
 }
 
-function mapSeverityToErrorCtor(severity: ErrorSeverity) {
-  switch (severity) {
-    case ErrorSeverity.InvalidInput:
-      return InvalidInputError;
-    case ErrorSeverity.Todo:
-      return TodoError;
-    default:
-      assertExhaustive(severity, `Unhandled severity level: ${severity}`);
-  }
-}
-
-function printPathCodeFrame(
-  reason: string,
-  severity: ErrorSeverity,
-  path: AnyNodePath
-) {
-  return path
-    .buildCodeFrameError(reason, mapSeverityToErrorCtor(severity))
-    .toString();
-}
-
-export class CompilerError {
-  severity: ErrorSeverity;
+/**
+ * Each bailout or invariant in HIR lowering creates an {@link CompilerErrorDetail}, which is then
+ * aggregated into a single {@link CompilerError} later.
+ */
+export class CompilerErrorDetail {
   reason: string;
+  severity: ErrorSeverity;
   /**
    * If a NodePath is provided, we will prefer Babel's built in codeframe error generation which
    * will print error markers in the correct location.
@@ -54,20 +51,49 @@ export class CompilerError {
   nodePath: AnyNodePath | null;
 
   constructor(options: CompilerErrorOptions) {
-    this.severity = options.severity;
     this.reason = options.reason;
+    this.severity = options.severity;
     this.nodePath = options.nodePath;
   }
 
-  toString(): string {
-    const buffer = [];
-    if (this.nodePath != null) {
+  get errorMessage(): string {
+    const buffer = [`${this.severity}: ${this.reason}`];
+    if (this.nodePath != null && this.nodePath.node?.loc != null) {
       buffer.push(
-        printPathCodeFrame(this.reason, this.severity, this.nodePath)
+        ` (${this.nodePath.node.loc.start.line}:${this.nodePath.node.loc.end.line})`
       );
-    } else {
-      buffer.push(`${this.severity}: ${this.reason}`);
     }
-    return `[ReactForget] ${buffer.join("")}`;
+    return buffer.join("");
+  }
+
+  get codeFrame() {
+    if (this.nodePath == null) {
+      return this.errorMessage;
+    }
+    try {
+      return this.nodePath
+        .buildCodeFrameError(this.reason, mapSeverityToErrorCtor(this.severity))
+        .toString();
+    } catch {
+      return this.errorMessage;
+    }
+  }
+
+  toString(): string {
+    return `[ReactForget] ${this.errorMessage}`;
+  }
+}
+
+export class CompilerError extends Error {
+  details: CompilerErrorDetail[] = [];
+
+  constructor(details: CompilerErrorDetail[], ...args: any[]) {
+    super(...args);
+    this.details = details;
+    this.message = this.toString();
+  }
+
+  override toString() {
+    return this.details.map((detail) => detail.toString()).join("\n\n");
   }
 }

compiler/forget/src/CompilerPipeline.ts

@@ -6,8 +6,8 @@
  */
 import { NodePath } from "@babel/traverse";
 import * as t from "@babel/types";
+import { CompilerError } from "./CompilerError";
 import {
-  Environment,
   HIRFunction,
   lower,
   mergeConsecutiveBlocks,
@@ -46,9 +46,8 @@ export type CompilerPipelineValue =
 export function* run(
   func: NodePath<t.FunctionDeclaration>
 ): Generator<CompilerPipelineValue, t.Function> {
-  const lowering = lower(func).orElse((errors) => {
-    const msg = errors.map((error) => error.toString()).join("\n\n");
-    throw new Error(msg);
+  const lowering = lower(func).orElse((details) => {
+    throw new CompilerError(details);
   });
 
   const hir = lowering.unwrap();

compiler/forget/src/HIR/BuildHIR.ts

@@ -7,7 +7,7 @@
 
 import { NodePath, Scope } from "@babel/traverse";
 import * as t from "@babel/types";
-import { CompilerError, ErrorSeverity } from "../CompilerError";
+import { CompilerErrorDetail, ErrorSeverity } from "../CompilerError";
 import { Err, Ok, Result } from "../lib/Result";
 import { assertExhaustive } from "../Utils/utils";
 import {
@@ -47,7 +47,7 @@ import HIRBuilder, { Environment } from "./HIRBuilder";
  */
 export function lower(
   func: NodePath<t.Function>
-): Result<HIRFunction, CompilerError[]> {
+): Result<HIRFunction, CompilerErrorDetail[]> {
   const env = new Environment();
   const builder = new HIRBuilder(env);
 

compiler/forget/src/HIR/HIRBuilder.ts

@@ -8,7 +8,7 @@
 import { NodePath } from "@babel/traverse";
 import * as t from "@babel/types";
 import invariant from "invariant";
-import { CompilerError, CompilerErrorOptions } from "../CompilerError";
+import { CompilerErrorDetail, CompilerErrorOptions } from "../CompilerError";
 import { logHIR } from "../Utils/logger";
 import { assertExhaustive } from "../Utils/utils";
 import { getOrAddGlobal } from "./Globals";
@@ -87,7 +87,7 @@ export default class HIRBuilder {
   #bindings: Map<string, { node: t.Identifier; identifier: Identifier }> =
     new Map();
   #env: Environment;
-  errors: CompilerError[] = [];
+  errors: CompilerErrorDetail[] = [];
 
   get nextIdentifierId() {
     return this.#env.nextIdentifierId;
@@ -415,10 +415,10 @@ export default class HIRBuilder {
     invariant(false, "Expected a loop to be in scope");
   }
 
-  pushError(options: CompilerErrorOptions): CompilerError {
-    const error = new CompilerError(options);
-    this.errors.push(error);
-    return error;
+  pushError(options: CompilerErrorOptions): CompilerErrorDetail {
+    const detail = new CompilerErrorDetail(options);
+    this.errors.push(detail);
+    return detail;
   }
 
   hasErrors(): boolean {

compiler/forget/src/__tests__/hir-test.ts

@@ -10,6 +10,7 @@
 import { wasmFolder } from "@hpcc-js/wasm";
 import path from "path";
 import runReactForgetBabelPlugin from "../Babel/RunReactForgetBabelPlugin";
+import { CompilerError } from "../CompilerError";
 import { toggleLogging } from "../Utils/logger";
 import generateTestsFromFixtures from "./test-utils/generateTestsFromFixtures";
 
@@ -98,10 +99,13 @@ ${outputs.join("\n")}
 });
 
 function formatErrorOutput(error: Error): string {
-  // Babel outputs absolute paths of the filename in the error mesage, which means fixtures will
-  // contain paths that only pertain to your local machine. Strip it just here because that info
-  // is still useful in real world usage of the Babel plugin.
-  error.message = error.message.replace(/^\/.*?:\s/, "");
+  if (error instanceof CompilerError) {
+    error.message = error.details
+      .map((detail) => `[ReactForget] ${detail.codeFrame}`)
+      .join("\n\n");
+  } else {
+    error.message = error.message.replace(/^\/.*?:\s/, "");
+  }
   return `
 ## Error
 

compiler/forget/src/index.ts

@@ -5,6 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 export { default as BabelPlugin } from "./Babel/BabelPlugin";
+export { ErrorSeverity } from "./CompilerError";
 export { compile, run } from "./CompilerPipeline";
 export { printHIR } from "./HIR";
 export { printReactiveFunction } from "./ReactiveScopes";