mesonbuild/meson

error when program is not found is not useful

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#2029 opened on Jul 3, 2017

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bughelp wanted

Description

I have a tags target:

run_target('tags', command : ['etags', '-o', '@0@/@1@'.format(meson.source_root(), 'TAGS')] + all_files)

(The presence of etags is not checked first with find_program on purpose: I want the target to be always there, and just fail with an error message is the program is not found. And I don't want to spam normal builds with a message about a missing etags program, because most users won't need it.)

When this target is executed and ctags is not installed, the message is useless:

$ ninja -C build ctags
[0/1] Running external command ctags.
Could not execute command "ctags".
FAILED: ctags 
'/usr/bin/python3' '/home/zbyszek/src/meson/meson.py' '--internal' 'commandrunner' '/home/zbyszek/src/casync' '/home/zbyszek/src/casync/build' '' '/home/zbyszek/src/meson/mesonintrospect.py' 'ctags' '-o' '/home/zbyszek/src/casync/tags' ...
ninja: build stopped: subcommand failed.

I'd expect the usual:

meson: ‘ctags’: No such file or directory

Contributor guide

Tech stack
python
Domain
build systemtooling
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
under 1 hour
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Basic understanding of Meson build systemFamiliarity with Python error handling
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
80
Research direction
Investigate the Meson command runner implementation in mesonbuild/scripts/commandrunner.py. Look for the string "Could not execute command" and the surrounding error handling. Improve the error message to include the program name and the actual OS error (e.g., 'No such file or directory'). Ensure the change is localized and does not affect other functionality.