MSBuild - Don't run VsTsc/recompile all files if no TypeScript files have been changed

[chrisdieckhaus]

We have a .NET MVC project with a TypeScript front-end, using tsc to compile files during build. After investigation, it appears that nearly half of our build time is occuring due to the CompileTypeScriptWithTSConfig target, task VsTsc.

Expected behavior:
If no typescript files have been updated, VsTsc should not be run, since there is no need to recompile all the changed files.

Stretch expected behavior:
If I update a TypeScript file and build, only that file should be recompiled, since no other files have changed (similar to the behavior of tsc --watch. After doing some searching, I think this might not be possible, but it's worth a shot.

Actual behavior:
On build, VsTsc is always called and all TypeScript files are recompiled, regardless of whether or not any of them have changed since last build.

Search Terms:
msbuild, vstsc, incremental build, incremental compile, compile on build, visual studio

[mhegazy]

//cc @uniqueiniquity

We have recently made changes to the tasks/targets to optimize this path. what version of TS are you using?

[chrisdieckhaus]

2.6.2. Has this been addressed in a later release?

[chrisdieckhaus]

Upgraded to 2.7.2 and that seems to have made a big improvement. Closing this issue.

[chrisdieckhaus]

So after updating to 2.7.2, our VsTsc compile time has dropped, between 33-50% faster. That being said, VsTsc is still compiling files regardless of whether or not any ts files have actually been updated. Are there any plans to make VsTsc smart enough to skip compilation if nothing has changed?

Looking through Microsoft.TypeScript.targets, it appears that VsTsc is still being run in the PreComputeCompileTypeScriptWithTSConfig target to generate the inputs and outputs required to incrementally build the CopmileTypeScriptWithTSConfig target. I guess that means there's no scenario in which VsTsc is never run?

[uniqueiniquity]

@chrisdieckhaus That's correct. When used in the PreComputeCompileTypeScript(WithTSConfig) scenario, VsTsc isn't actually spending time compiling your files; we're only determining inputs and outputs as you noted.

[chrisdieckhaus]

Gotcha, that makes sense. Thanks!