[wasm] Check if python is installed when installing the workload

[lewing]

Right now the build expects python to be in the path on linux but ends up checking this by running emcc --version and not surfacing the error text.

[ghost]

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Issue Details

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Right now the build expects python to be in the path on linux but ends up checking this by running emcc --version and not surfacing the error text.

Author:	lewing
Assignees:	radical
Labels:	arch-wasm, area-Build-mono
Milestone:	6.0.0

[lewing]

Likely the cause of #54342

[radical]

1. [wasm] Build improvements #61276 surfaces the output of emcc --version correctly, so the error would show up for the user
2. But we should also check for python when installing the workload

[radical]

But we should also check for python when installing the workload

This needs to be done on the sdk side, so closing this in favor of - dotnet/sdk#26050 .

[radical]

Doing it in WorkloadManifest.targets would mean that we do it for every build. Though maybe we can add some sentinel file in obj, so we don't have to do that more than once for incremental builds.

[lewing]

I was thinking something simple like <OnError ExecuteTargets="SanityCheckEmsdk"/>

[radical]

I was thinking something simple like <OnError ExecuteTargets="SanityCheckEmsdk"/>

That we essentially do:

runtime/src/mono/wasm/build/WasmApp.Native.targets

Lines 474 to 486 in e43e315

	<Exec Command="$(_EmccVersionCommand)" WorkingDirectory="$(_WasmIntermediateOutputPath)" EnvironmentVariables="@(EmscriptenEnvVars)" ConsoleToMsBuild="true" StandardOutputImportance="Low" IgnoreExitCode="true">
	<Output TaskParameter="ConsoleOutput" ItemName="_VersionLines" />
	<Output TaskParameter="ExitCode" PropertyName="_EmccVersionExitCode" />
	</Exec>
	<!-- If `emcc -version` failed, then run it again, so we can surface the output as *Errors*. This allows the errors to show up correctly,
	versus trying to use the output lines with the Error task -->
	<Exec Condition="$(_EmccVersionExitCode) != '0'"
	Command="$(_EmccVersionCommand)"
	WorkingDirectory="$(_WasmIntermediateOutputPath)"
	EnvironmentVariables="@(EmscriptenEnvVars)"
	CustomErrorRegularExpression=".*"
	/>

First we run emcc --version, and if that fails then we run it again but surface the output to the user as errors.

This will show emcc --version failing due to missing python:

emcc --version
unable to find python in $PATH

So, if we are not adding a check at workload install time, then I think there is nothing else to be done here. But please re-open if you don't agree.