feat: use __rspack_dev_server_uri to communicate to right dev server

[stormslowly]

Summary

This update depends on Pull Request #53.

This change enhances the developer experience for users running the development server on a proxied site rather than on localhost.

For example, if the development server starts on a localhost auto port, and the user configures lazyCompilation: true (using the default settings), the development assets are proxied to a site like https://a.com.

Before

With lazy compilation enabled, requests would be sent to https://a.com/lazy-compilation-using-compilation-proxy.... These requests would fail, resulting in a blank page.

After

Requests will now be sent to http://127.0.0.1:8080/lazy-compilation-using-compilation-proxy...., allowing lazy compilation to function as expected.

Related Links

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

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[Copilot]

Pull request overview

This PR enhances the lazy compilation feature for web environments by adding support for __rspack_dev_server_uri. This allows the lazy compilation client to correctly communicate with the dev server when the application is running behind a proxy or on a different origin than localhost. The change ensures that relative URLs are properly resolved to the correct dev server location.

Key Changes

• Added logic to prepend __rspack_dev_server_uri to relative URLs in lazy compilation
• Only applies when URL is not already absolute (doesn't start with "http")
• Depends on rspack-dev-server PR #53 for the server-side implementation

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[Copilot]

Potential URL concatenation issue: When concatenating __rspack_dev_server_uri with urlBase, there's no handling for trailing/leading slashes. This could result in malformed URLs like http://example.com//path (double slash) or http://example.compath (missing slash).

Consider normalizing the URL concatenation:

var separator = __rspack_dev_server_uri.endsWith("/") || urlBase.startsWith("/") ? "" : "/";
urlBase = __rspack_dev_server_uri + separator + urlBase;

Or ensure proper slash handling:

urlBase = __rspack_dev_server_uri.replace(/\/$/, "") + "/" + urlBase.replace(/^\//, "");

Suggested change

	urlBase = __rspack_dev_server_uri + urlBase;
	urlBase = __rspack_dev_server_uri.replace(/\/$/, "") + "/" + urlBase.replace(/^\//, "");

[Copilot]

[nitpick] Consider adding a comment explaining the purpose of prepending __rspack_dev_server_uri to help future maintainers understand this logic. For example:

// When running behind a proxy or on a different origin, use the dev server URI
// provided by rspack-dev-server to construct the full URL for lazy compilation
if (
	!urlBase.startsWith("http") &&
	typeof __rspack_dev_server_uri !== "undefined"
) {
	urlBase = __rspack_dev_server_uri + urlBase;
}

Suggested change

	if (
	!urlBase.startsWith("http") &&
	typeof __rspack_dev_server_uri !== "undefined"
	) {
	urlBase = __rspack_dev_server_uri + urlBase;
	}

[github-actions]

📦 Binary Size-limit

Comparing e4661da to chore: release v1.6.5 (#12278) by jinrui

🙈 Size remains the same at 47.65MB

[codspeed-hq]

CodSpeed Performance Report

Merging #12281 will not alter performance

_{Comparing feat/use_dev_sever_uri (e4661da) with main (01fbb08)}

Summary

✅ 17 untouched

[chenjiahan]

This is not a reasonable design, because most higher-level tools (including Rsbuild and Modern.js) do not use @rspack/dev-server.

[stormslowly]

This is not a reasonable design, because most higher-level tools (including Rsbuild and Modern.js) do not use @rspack/dev-server.

I agree that high-level tools should configure RSPack correctly.

However, there is a key difference in this case. We need to know the final hostname and port of the development server. The hostname and port are determined by the dev server; for example, if the port is configured to auto.

For Lazy Compilation, if the serverUrl is not configured properly, the application will go blank. To ensure Lazy Compilation works as expected, it is crucial to direct active requests to the correct server.

I believe there are two ways to achieve this:

Config Phase

Before the compiler starts running, configure the serverUrl with the correct hostname and port. Since the appropriate hostname and port come from the dev server, determining the right configuration at that moment may not be straightforward.

Runtime Phase

During runtime, the hostname and port for active lazy compilation are determined. Therefore, Lazy Compilation needs a way to obtain the dev server information. A "magic variable" is one potential solution. Without the variable __rspack_dev_server_uri, Lazy Compilation will default to using the browser's URL hostname and port. If the variable exists, it will utilize the configured value.

For Rsbuild and Modern.js, they can either adapt to this magic variable or opt for the configuration phase solution.