feat: Form code frame from sourcemaps for prerender errors

package.json

@@ -42,19 +42,23 @@
 		"kolorist": "^1.8.0",
 		"magic-string": "0.30.5",
 		"node-html-parser": "^6.1.10",
-		"resolve": "^1.22.8"
+		"resolve": "^1.22.8",
+		"source-map": "^0.7.4",
+		"stack-trace": "^1.0.0-pre2"
 	},
 	"peerDependencies": {
 		"@babel/core": "7.x",
 		"vite": "2.x || 3.x || 4.x || 5.x"
 	},
 	"devDependencies": {
 		"@babel/core": "^7.15.8",
+		"@types/babel__code-frame": "^7.0.6",
 		"@types/babel__core": "^7.1.14",
 		"@types/debug": "^4.1.5",
 		"@types/estree": "^0.0.50",
 		"@types/node": "^14.14.33",
 		"@types/resolve": "^1.20.1",
+		"@types/stack-trace": "^0.0.33",
 		"lint-staged": "^10.5.4",
 		"preact": "^10.19.2",
 		"preact-iso": "^2.3.2",

src/prerender.ts

@@ -1,9 +1,11 @@
 import path from "node:path";
-
 import { promises as fs } from "node:fs";
 
 import MagicString from "magic-string";
 import { parse as htmlParse } from "node-html-parser";
+import { SourceMapConsumer } from "source-map";
+import { parse as StackTraceParse } from "stack-trace";
+import { codeFrameColumns } from "@babel/code-frame";
 
 import type { Plugin, ResolvedConfig } from "vite";
 
@@ -116,6 +118,9 @@ export function PrerenderPlugin({
 		apply: "build",
 		enforce: "post",
 		configResolved(config) {
+			// Enable sourcemaps at least for prerendering for usable error messages
+			config.build.sourcemap = true;
+
 			viteConfig = config;
 		},
 		async options(opts) {
@@ -212,7 +217,7 @@ export function PrerenderPlugin({
 				JSON.stringify({ type: "module" }),
 			);
 
-			let prerenderEntry;
+			let prerenderEntry: OutputChunk | undefined;
 			for (const output of Object.keys(bundle)) {
 				if (!/\.js$/.test(output) || bundle[output].type !== "chunk") continue;
 
@@ -222,7 +227,7 @@ export function PrerenderPlugin({
 				);
 
 				if ((bundle[output] as OutputChunk).exports?.includes("prerender")) {
-					prerenderEntry = bundle[output];
+					prerenderEntry = bundle[output] as OutputChunk;
 				}
 			}
 			if (!prerenderEntry) {
@@ -238,22 +243,61 @@ export function PrerenderPlugin({
 				);
 				prerender = m.prerender;
 			} catch (e) {
-				const isReferenceError = e instanceof ReferenceError;
+				const stack = StackTraceParse(e as Error).find(s =>
+					s.getFileName().includes(tmpDir),
+				);
 
-				const message = `
+				const isReferenceError = e instanceof ReferenceError;
+				let message = `\n
 					${e}
 
 					This ${
 						isReferenceError ? "is most likely" : "could be"
 					} caused by using DOM/Web APIs which are not available
-					available to the prerendering process which runs in Node. Consider
+					available to the prerendering process running in Node. Consider
 					wrapping the offending code in a window check like so:
 
 					if (typeof window !== "undefined") {
 						// do something in browsers only
 					}
 				`.replace(/^\t{5}/gm, "");
 
+				const sourceMapContent = prerenderEntry.map;
+				if (stack && sourceMapContent) {
+					await SourceMapConsumer.with(
+						sourceMapContent,
+						null,
+						async consumer => {
+							let { source, line, column } = consumer.originalPositionFor({
+								line: stack.getLineNumber(),
+								column: stack.getColumnNumber(),
+							});
+
+							if (!source || line == null || column == null) {
+								message += `\nUnable to locate source map for error!\n`;
+								this.error(message);
+							}
+
+							// `source-map` returns 0-indexed column numbers
+							column += 1;
+
+							const sourcePath = path.join(
+								viteConfig.root,
+								source.replace(/^(..\/)*/, ""),
+							);
+							const sourceContent = await fs.readFile(sourcePath, "utf-8");
+
+							const frame = codeFrameColumns(sourceContent, {
+								start: { line, column },
+							});
+							message += `
+							> ${sourcePath}:${line}:${column}\n
+							${frame}
+						`.replace(/^\t{7}/gm, "");
+						},
+					);
+				}
+
 				this.error(message);
 			}