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Improve error message for conflicting priorities

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I find the error message 'nix-env --set-flag priority NUMBER PKGNAME'
not as helpful as it could be :
- doesn't share the current priorities
- doesn't say that the command must be run on the already installed
PKGNAME (which is confusing the first time)
- the doc needs careful reading:
"If there are multiple derivations matching a name in args that have the same name (e.g., gcc-3.3.6 and gcc-4.1.1), then the derivation with the highest priority is used."
if one stops reading there, he is screwed. Salvation comes with reading "A derivation can define a priority by declaring the meta.priority attribute. This attribute should be a number, with a higher value denoting a lower priority. The default priority is 0."
To sum it up, lower number wins. I tried to convey this idea in the
message too.
This commit is contained in:
Matthieu Coudron 2017-09-21 10:25:20 +09:00
parent 84f112b1c8
commit 6920c23701
1 changed files with 4 additions and 3 deletions
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7
src/buildenv/buildenv.cc
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@ -74,10 +74,11 @@ static void createLinks(const Path & srcDir, const Path & dstDir, int priority)
auto prevPriority = priorities[dstFile];
if (prevPriority == priority)
throw Error(format(
"collision between '%1%' and '%2%'; "
"use 'nix-env --set-flag priority NUMBER PKGNAME' "
"Packages '%1%' and '%2%' have the same priority '%3%'"
"use 'nix-env --set-flag priority NUMBER INSTALLED_PKGNAME' "
"to change the priority of one of the conflicting packages"
) % srcFile % target);
" ('0' being the highest priority)"
) % srcFile % target % priority);
if (prevPriority < priority)
continue;
if (unlink(dstFile.c_str()) == -1)