Make a test compatible across python versions.

[smmalis37]

Progress on #65063

This PR allows this test to work on both python2 and python3, and it also allows ./x.py test to fully complete on my system without python2 installed at all.

[rust-highfive]

r? @alexcrichton

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[alexcrichton]

@bors: r+

[bors]

📌 Commit f37f423 has been approved by alexcrichton

[JohnTitor]

Seems failed in #66421 (comment)
@bors r-

[smmalis37]

If I'm reading that right there's no python command on i686-gnu, but there is on other architectures? Does someone who's more familiar with the CI environments know what happened here?

[mati865]

It's because installing python2.7 with apt installs only the suffixed binaries. python without suffix is provided by python package which points to python2.7 in currently used distributions but that might change in Ubuntu 20.04 as there are plans to remove Python 2 altogether.
This affects other builders as well, scrips are located in https://github.com/rust-lang/rust/tree/master/src/ci/docker

The decision what to do here is up to reviewer.

[alexcrichton]

I don't know how best to fix this, but it looks like the CI environment doesn't have a python executable.

[smmalis37]

The test failed on Linux i686-gnu but succeeded on Linux x86_64-gnu-llvm-6.0. Comparing the packages installed at src/ci/docker/i686-gnu/Dockerfile vs src/ci/docker/x86_64-gnu-llvm-6.0/Dockerfile shows these packages installed on x86_64 but not i686:

g++ vs g++-multilib
llvm-6.0-tools
libedit-dev
libssl-dev
pkg-config
zlib1g-dev

It looks like llvm-6.0-tools depends on python, which means we get lucky on that platform. I'm assuming something similar is true for the other successful platforms. I'll change the makefile back to calling python2.7, and that can switch when all the infrastructure updates to python3. The change to the actual python file will still help, since it won't need to be changed at that point.

[alexcrichton]

@bors: r+

[bors]

📌 Commit 56f9212 has been approved by alexcrichton

[bors]

⌛ Testing commit 56f9212 with merge 9966af3...

[bors]

☀️ Test successful - checks-azure
Approved by: alexcrichton
Pushing 9966af3 to master...