Timestamp based check for changes to HTML template

[dwoznicki]

As of webpack version 4, isCompilationCached no longer appears to be a reliable method of checking whether a template file has been changed. Instead, we can check compilation.fileTimestamps to see when the template file was last modified.
For a 25 html page project, I've found this change reduces the rebuild time from ~3000ms to ~700ms in --watch mode.

NOTE: this commit fails the build test because WebpackRecompilationSimulator.simulateFileChange does not change the compilation.fileTimestamps object.
One way to solve this might be to have simulateFileChange write to the source file and then immediately revert the changes. Another might be to initialize the HtmlWebpackPlugin with the temp file as the template instead of the source file. Both require making changes to webpack-recompilation-simulator, which I'm not sure how to build.
In practice, I've found this commit to work as expected with webpack --watch.

[jantimon]

Wow cool :)

Actually the my webpack-recompilation-simulator will really change a file:

https://github.com/jantimon/webpack-recompilation-simulator/blob/ae4e111f41124f292327ce716e4f145c7f898e54/src/index.js#L34-L51

If there is a bug in the webpack-recompilation-simulator we would have to fix it first.. otherwise it will be really hard to test caching.

There is a little bit more todo for your timestamp logic - right now you are only checking for the timestamp of the template file but not for the timestamp of its dependencies.

Also we should try to prepare your change for #953

[dwoznicki]

I actually have a solution to check for changes to dependencies, but it causes the “HtmlWebpackPluginCaching won’t recompile if only a javascript file was changed” test to fail. Do we really want the html file to rebuild when a js dependency is changed? I guess so to change the options.hash hash. Anyway, I’ll make another commit later.

[jantimon]

Right now I am fiddling around with a new child compiler but I need some more time to get it working.

[jantimon]

@dwoznicki I just opened #967 which fixes the first part of the issue.

Right now it will revoke the cache in the emit phase:

html-webpack-plugin/index.js

Line 125 in 66ae631

childCompiler.clearCache(compiler);

Instead we should store the compilation dependencies during the child compiler compilation and check in the compile function if it needs to rebuild.

I also added an array which holds all files used for the template generation:
da2d211

What do you think?

[dwoznicki]

Cool! That should work quite well. I'm going to grab your changes in feature/single-compiler and make another pull request actually since it strikes me that I'm attempting to merge into master instead of webpack-4 here.

[lock]

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