build-system: Support alternate sourcemap URLs

[mdmower]

Support --sourcemap_url flag in gulp dist to customize the base URL
used in sourcemap links. The value passed to this flag should include a
placeholder {version} that will be replaced with the actual version.

For example:

gulp dist --sourcemap_url "https://example.com/{version}/root/" --version_override "12345"

would set the amp.js sourcemap URL to

https://example.com/12345/root/src/amp.js

This feature improves support for self-hosting the AMP runtime. It will be documented in the "Hosting the AMP framework" guide.

[mdmower]

@rsimha Could you help me understand an inconsistency I'm seeing between the sourcemap served from cdn.ampproject.org and that served from cdn.ampproject.org/rtv/<rtv>?

[rsimha]

@rsimha Could you help me understand an inconsistency I'm seeing between the sourcemap served from cdn.ampproject.org and that served from cdn.ampproject.org/rtv/<rtv>?

I think this might be a known problem that @jridgewell and @rcebulko are in the process of fixing. Will let them chime in here.

[mdmower]

@rsimha Could you help me understand an inconsistency I'm seeing between the sourcemap served from cdn.ampproject.org and that served from cdn.ampproject.org/rtv/<rtv>?

I think this might be a known problem that @jridgewell and @rcebulko are in the process of fixing. Will let them chime in here.

Thanks for deciphering my question. I accidentally hit shift+enter which posted my comment. Here's the discrepancy I'm seeing:

Using amp.js as a sample, sometimes there an extra /src in the URLs:

https://cdn.ampproject.org/rtv/012004041903580/v0.js.map --> https://raw.githubusercontent.com/ampproject/amphtml/2004041903580/src/src/amp.js

https://cdn.ampproject.org/rtv/012004030010070/v0.js.map --> https://raw.githubusercontent.com/ampproject/amphtml/2004030010070/src/amp.js

https://cdn.ampproject.org/v0.js.map --> https://raw.githubusercontent.com/ampproject/amphtml/2004030010070/src/amp.js

When I build locally, with gulp dist --type --version_override 2004030010070 --> https://raw.githubusercontent.com/ampproject/amphtml/2004030010070/src/src/amp.js

[kristoferbaxter]

See #27665 for explanation of why this /src/src issue exists.

You'll want to pull in that PR's changes after it lands before continuing.

[jridgewell]

I think this can actually be merged when ready, and I'll update my PR to incorporate it.

[mdmower]

I think this can actually be merged when ready, and I'll update my PR to incorporate it.

@rsimha - Do you have a preference about the order in which the PRs are committed? Is the suggestion to use a placeholder {version} in the URL acceptable (see PR message)?

[rsimha]

@rsimha - Do you have a preference about the order in which the PRs are committed? Is the suggestion to use a placeholder {version} in the URL acceptable (see PR message)?

@mdmower I assume this is the only place where the version passed in via the command line flag is substituted, correct?

Regarding the actual substitution string, we already use $internalRuntimeVersion$ in our source code:

amphtml/src/internal-version.js

Lines 17 to 28 in bb93693

	/**
	* Returns the internal AMP runtime version. Note that this is not the RTV,
	* which is a prefix and the runtime version.
	*
	* The call sites for this function are replaced with a compile time constant
	* string.
	*
	* @return {string}
	*/
	export function internalRuntimeVersion() {
	return '$internalRuntimeVersion$';
	}

Would it work if you used the same string for URL substitution as well?

gulp dist --sourcemap_url "https://example.com/$internalRuntimeVersion$/root/" --version_override "12345"

[mdmower]

I assume this is the only place where the version passed in via the command line flag is substituted, correct?

Correct.

we already use $internalRuntimeVersion$... Would it work if you used the same string for URL substitution as well?

Thanks for pointing that out! Sure, I'll make the change.

[mdmower]

@rsimha Actually, I'm questioning whether string $internalRuntimeVersion$ is the best choice for a user-facing flag. I've tried to make a consistent distinction between a version and a runtime version, reserving the latter to mean (config + version).

[rsimha]

Gotcha. I have no strong personal preference here, since it is a limited use case that you are more familiar with. (Perhaps $version$ is a good compromise?)

Once decided, we should mention the actual substitution string in the flag notes for --sourcemap_url.

[mdmower]

I opted to keep {version} since shells would treat $version$ like an environment variable $version with an appended $ in common use cases like

gulp dist --sourcemap_url "https://example.com/$version$/"

[rsimha]

This PR LGTM, modulo the version substitution changes. Will let @jridgewell provide final approval, since he will need to incorporate this change into his sourcemaps fix.

[jridgewell]

Merging so that I can rebase on it.