x.py: Give a more helpful error message if curl isn't installed

[jyn514]

Before:

Updating only changed submodules
Submodules updated in 0.01 seconds
Traceback (most recent call last):
  File "./x.py", line 11, in <module>
    bootstrap.main()
  ...
  File "/home/joshua/src/rust/src/bootstrap/bootstrap.py", line 137, in run
    ret = subprocess.Popen(args, **kwargs)
  File "/usr/lib/python2.7/subprocess.py", line 394, in __init__
    errread, errwrite)
  File "/usr/lib/python2.7/subprocess.py", line 1047, in _execute_child
    raise child_exception
OSError: [Errno 2] No such file or directory

After:

Updating only changed submodules
Submodules updated in 0.01 seconds

spurious failure, trying again

spurious failure, trying again

spurious failure, trying again

spurious failure, trying again
failed to run: curl -s -y 30 -Y 10 --connect-timeout 30 --retry 3 -Sf -o /tmp/tmpSWF21P.sha256 https://static.rust-lang.org/dist/2020-04-22/rust-std-beta-x86_64-unknown-linux-gnu.tar.gz.sha256: [Errno 2] No such file or directory
Build completed unsuccessfully in 0:00:00

[rust-highfive]

r? @Mark-Simulacrum

(rust_highfive has picked a reviewer for you, use r? to override)

[jyn514]

I'm not sure that the RuntimeError is the right way to go about things since other parts of the program seem to assume that means a spurious failure ... I'm not sure how else to give a reasonable message though. Maybe it would be better to just print the error and exit unconditionally?

[Mark-Simulacrum]

Hm, we can probably do the same thing we do for git? IIRC we run git --version and if that fails assume git isn't installed or won't do what we need.

[jyn514]

Ooh that looks like a good way to do it! I see that sort of thing is repeated a lot (also for uname, isainfo) - do you mind if I factor it out into a function at the same time?

[Mark-Simulacrum]

Not at all, please do!

[jyn514]

The new output is

Updating only changed submodules
Submodules updated in 0.01 seconds
error: `curl` is not found, please make sure it's installed and in the path.

[jyn514]

I realized that this will now give a misleading error if you have the command in path but the command failed (e.g. maybe -s isn't a valid argument to uname). I'm going to print out the entire command that failed instead so it's easier to debug.

[jyn514]

New output:

Updating only changed submodules
Submodules updated in 0.01 seconds
error: `curl --version` is not found, please make sure it's installed and in the path.

[Mark-Simulacrum]

Hm, can we perhaps say:

``
Unable to run curl --version: OSError: not found
Please make sure it's installed and in PATH.

[jyn514]

How does this look?

error: unable to run `curl --version`: [Errno 2] No such file or directory
Please make sure it's installed and in the path.

[Mark-Simulacrum]

Please squash the commits into one; r=me after that.

[Mark-Simulacrum]

@bors r+ rollup

[bors]

📌 Commit 9bcf409 has been approved by Mark-Simulacrum