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feat: production sourcemaps #16412

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Merged
Rich-Harris merged 10 commits into from
Jul 19, 2026
Merged

feat: production sourcemaps #16412

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2198a09
WIP production sourcemaps
Rich-Harris Jul 18, 2026
a6e7225
fix
Rich-Harris Jul 18, 2026
708436b
changeset
Rich-Harris Jul 18, 2026
8f78d65
server sourcemaps by default
Rich-Harris Jul 18, 2026
02afeaf
Merge branch 'version-3' into sourcemaps
teemingc Jul 19, 2026
3e2332a
better regex
Rich-Harris Jul 19, 2026
7633626
unused
Rich-Harris Jul 19, 2026
eeb9b19
redundant
Rich-Harris Jul 19, 2026
9fbe784
hoist
Rich-Harris Jul 19, 2026
955ae8c
DRY
Rich-Harris Jul 19, 2026
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5 changes: 5 additions & 0 deletions .changeset/brave-files-cheat.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
---
'@sveltejs/kit': minor
---

feat: support sourcemaps in production
115 changes: 2 additions & 113 deletions packages/kit/src/core/postbuild/prerender.js
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Original file line number Diff line number Diff line change
@@ -1,7 +1,6 @@
import { existsSync, readFileSync, statSync, writeFileSync } from 'node:fs';
import { SourceMap } from 'node:module';
import { dirname, join, relative, resolve as resolve_path } from 'node:path';
import { fileURLToPath, pathToFileURL } from 'node:url';
import { dirname, join } from 'node:path';
import { pathToFileURL } from 'node:url';
import { mkdirp, walk } from '../../utils/filesystem.js';
import { posixify } from '../../utils/os.js';
import { noop } from '../../utils/functions.js';
Expand All @@ -17,7 +16,6 @@ import * as devalue from 'devalue';
import { createReadableStream } from '@sveltejs/kit/node';
import generate_fallback from './fallback.js';
import { stringify_remote_arg } from '../../runtime/shared.js';
import { SRC_ROOT } from '../../constants.js';
import { log_response } from '../../exports/vite/utils.js';

export default forked(import.meta.url, prerender);
Expand Down Expand Up @@ -50,7 +48,6 @@ async function prerender({ hash, out, manifest_path, metadata, verbose, env, vit
// essential we do this before analysing the code
internal.set_building();
internal.set_prerendering();
internal.set_fix_stack_trace(adjust_stack_trace);

// `set_env` and `Server` live in modules that import the user's `src/env` config. We import them
// *after* `set_building()` so that `building`-dependent expressions resolve correctly
Expand Down Expand Up @@ -119,114 +116,6 @@ async function prerender({ hash, out, manifest_path, metadata, verbose, env, vit
}
}

/** @type {Map<string, { map: SourceMap; directory: string } | null>} */
const source_maps = new Map();
/** @type {Map<string, Array<string | undefined>>} */
const source_regions = new Map();

/** @param {string} file */
function get_source_map(file) {
if (source_maps.has(file)) return source_maps.get(file);

let source;
let directory = dirname(file);
try {
const code = readFileSync(file, 'utf8');
const matches = Array.from(code.matchAll(/\/\/[#@]\s*sourceMappingURL=(\S+)/g));
const url = matches.at(-1)?.[1];

if (url?.startsWith('data:')) {
const comma = url.indexOf(',');
const metadata = url.slice(5, comma);
const data = url.slice(comma + 1);
source = metadata.endsWith(';base64')
? Buffer.from(data, 'base64').toString()
: decodeURIComponent(data);
} else {
const map_file = url ? resolve_path(dirname(file), decodeURIComponent(url)) : `${file}.map`;
if (existsSync(map_file)) {
directory = dirname(map_file);
source = readFileSync(map_file, 'utf8');
}
}

const source_map = source ? { map: new SourceMap(JSON.parse(source)), directory } : null;
source_maps.set(file, source_map);
return source_map;
} catch {
source_maps.set(file, null);
return null;
}
}

/** @param {unknown} error */
function adjust_stack_trace(error) {
if (!(error instanceof Error) || !error.stack) return;

error.stack = error.stack
.split('\n')
.map((line) => {
const match = line.match(/(file:\/\/\/.*):(\d+):(\d+)(\)?)$/);
if (!match) return line;

const file = fileURLToPath(match[1]);
// Filter out internal stack trace lines
if (file.includes('/svelte/src/internal/server/') || file.startsWith(SRC_ROOT)) {
return null;
}
// Only annotate files from our own server directory
if (!file.startsWith(`${out}/server/`)) return line;

const source_map = get_source_map(file);
const entry = source_map?.map.findEntry(Number(match[2]) - 1, Number(match[3]) - 1);
if (
source_map &&
entry &&
'originalSource' in entry &&
entry.originalSource &&
typeof entry.originalLine === 'number' &&
typeof entry.originalColumn === 'number'
) {
const source = entry.originalSource.startsWith('file:')
? fileURLToPath(entry.originalSource)
: resolve_path(source_map.directory, entry.originalSource);

// Filter out internal stack trace lines (gotta do this again here on the original)
if (source.includes('/svelte/src/internal/server/') || source.startsWith(SRC_ROOT)) {
return null;
}

const location = `${match[1]}:${match[2]}:${match[3]}`;
const original = `${posixify(relative(vite_config.root, source))}:${entry.originalLine + 1}:${entry.originalColumn + 1}`;

return line.replace(location, original);
}

let regions = source_regions.get(file);
if (!regions) {
/** @type {string | undefined} */
let source;
regions = readFileSync(file, 'utf8')
.split('\n')
.map((line) => {
// Vite will merge multiple files into one but add region markers
// with the original file names, which we try to extract here.
const start = line.match(/^\/\/#region (.+)$/);
if (start) source = start[1];
if (line === '//#endregion') source = undefined;
return source;
});
source_regions.set(file, regions);
}

const source = regions[Number(match[2]) - 1];
// Output is something like "at file:///... [src/routes/+page.svelte]"
return source ? `${line} [${source}]` : line;
})
.filter(Boolean)
.join('\n');
}

const OK = 2;
const REDIRECT = 3;

Expand Down
27 changes: 9 additions & 18 deletions packages/kit/src/exports/vite/index.js
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Original file line number Diff line number Diff line change
Expand Up @@ -401,6 +401,14 @@ function kit({ svelte_config }) {
// dev and preview config can be shared
/** @type {UserConfig} */
const new_config = {
environments: {
ssr: {
build: {
sourcemap:
config.environments?.ssr?.build?.sourcemap ?? config.build?.sourcemap ?? true
}
}
},
resolve: {
alias: [
{ find: '__SERVER__', replacement: `${generated}/server` },
Expand Down Expand Up @@ -1543,15 +1551,6 @@ function kit({ svelte_config }) {
},

async buildApp(builder) {
const sourcemap = builder.config.build.sourcemap;
const ssr_sourcemap = builder.environments.ssr.config.build.sourcemap;
const temporary_sourcemap = !(ssr_sourcemap ?? sourcemap);

if (temporary_sourcemap) {
// Temporarily override so that we get better stack traces for prerendering errors
builder.environments.ssr.config.build.sourcemap = 'hidden';
}

// clears the output directories
if (!builder.config.build.watch) {
rimraf(out);
Expand Down Expand Up @@ -1860,16 +1859,8 @@ function kit({ svelte_config }) {
// Unforeseen error, rethrow as-is
throw e;
}
} finally {
if (temporary_sourcemap) {
// If we did override it, set it back to false and remove the sourcemaps
builder.environments.ssr.config.build.sourcemap = ssr_sourcemap;

for (const file of fs.globSync(`${out}/server/**/*.js.map`)) {
fs.rmSync(file);
}
}
}

prerendered = prerender_results.prerendered;

await treeshake_prerendered_remotes(
Expand Down
15 changes: 2 additions & 13 deletions packages/kit/src/runtime/server/internal.js
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Original file line number Diff line number Diff line change
@@ -1,25 +1,12 @@
/** @import { SSRManifest } from '@sveltejs/kit'; */

/**
* @param {Error} _error
* @returns void
*/
export let fix_stack_trace = (_error) => {};

/**
* @type {((path: string) => ReadableStream<any>) | null}
*/
export let read_implementation = null;

export let manifest = /** @type {SSRManifest} */ (/** @type {unknown} */ (null));

/**
* @param {(error: Error) => void} fn
*/
export function set_fix_stack_trace(fn) {
fix_stack_trace = fn;
}

/**
* @param {(path: string) => ReadableStream<any>} fn
*/
Expand All @@ -34,3 +21,5 @@ export function set_read_implementation(fn) {
export function set_manifest(value) {
manifest = value;
}

export { fix_stack_trace, set_fix_stack_trace } from './sourcemaps.js';
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