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failure to resolve with equality requirement. #1800

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danburkert opened this issue Jul 11, 2015 · 1 comment · Fixed by #1804
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failure to resolve with equality requirement. #1800

danburkert opened this issue Jul 11, 2015 · 1 comment · Fixed by #1804

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@danburkert
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Cargo fails to resolve a dependency with an equality requirement if a newer version is published.

Steps to reproduce: clone tokio-rs/mio@eed4855 and change the dependency on libc from "0.1.8" to "=0.1.8". cargo build fails with the following error:

failed to select a version for `libc` (required by `mio`):
all possible versions conflict with previously selected versions of `libc`
  version 0.1.9 in use by libc v0.1.9
  possible versions to select: 0.1.8
This was referenced Jul 12, 2015
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@carllerche
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Woops, I thought this was the mio repo

@carllerche carllerche reopened this Jul 13, 2015
@alexcrichton alexcrichton mentioned this issue Jul 13, 2015
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alexcrichton added a commit to alexcrichton/cargo that referenced this issue Jul 17, 2015
@alexcrichton
Backtrack more aggressively when resolving
44eb16d 
Resolving a dependency graph may involve quite a bit of backtracking to select
different versions of crates, but the previous implementation of resolution
would not backtrack enough.

Once a dependency is completely resolved it's possible that any number of
candidates for its transitive dependencies were left out of the resolution
process (e.g. we didn't hit them yet). These candidates were not previously used
for backtracking (because resolution overall of the dependency finished), but
this commit alters the implementation to instead consider these as candidates
for backtracking.

Architecturally this changes the code to CPS to pass around a `finished`
continuation to allow tweaking the behavior whenever a dependency successfully
resolves. The key change is then that whenever a candidate for a dependency is
activated, we ensure the recursive step for the rest of the graph happens as a
sub-call. This means that if *anything* in the recursive call fails (including
some previous up-the-stack resolution) we'll retry the next candidate.

Closes rust-lang#1800
bors added a commit that referenced this issue Jul 17, 2015
@bors
Auto merge of #1804 - alexcrichton:aggressively-backtrack, r=brson
a10897c 
Resolving a dependency graph may involve quite a bit of backtracking to select
different versions of crates, but the previous implementation of resolution
would not backtrack enough.

Once a dependency is completely resolved it's possible that any number of
candidates for its transitive dependencies were left out of the resolution
process (e.g. we didn't hit them yet). These candidates were not previously used
for backtracking (because resolution overall of the dependency finished), but
this commit alters the implementation to instead consider these as candidates
for backtracking.

Architecturally this changes the code to CPS to pass around a `finished`
continuation to allow tweaking the behavior whenever a dependency successfully
resolves. The key change is then that whenever a candidate for a dependency is
activated, we ensure the recursive step for the rest of the graph happens as a
sub-call. This means that if *anything* in the recursive call fails (including
some previous up-the-stack resolution) we'll retry the next candidate.

Closes #1800
@MarkusJais MarkusJais mentioned this issue Aug 17, 2015
Closed
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Backtrack more aggressively when resolving alexcrichton/cargo
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@carllerche @danburkert