bug#51726: SWH: ‘lookup-origin-revision’ can miss tags

[Ludovic Courtès]

Quoting
<https://lists.gnu.org/archive/html/guix-devel/2021-10/msg00291.html>:

--8<---------------cut here---------------start------------->8---
> However, I get this:
>
> $ guix lint -c archival sway                    
> gnu/packages/wm.scm:1527:5: sway@1.5.1: scheduled Software Heritage archival

Indeed, I’m getting that as well.

Right now Sway’s origin refers to the “1.5.1” tag.

I found the problem:

scheme@(guile-user)> ,use(guix swh)
scheme@(guile-user)> (lookup-origin-revision "https://github.com/swaywm/sway"; 
"1.5.1")
$2 = #f
scheme@(guile-user)> (lookup-origin "https://github.com/swaywm/sway";)
$3 = #<<origin> visits-url: 
"https://archive.softwareheritage.org/api/1/origin/https://github.com/swaywm/sway/visits/";
 type: #<unspecified> url: "https://github.com/swaywm/sway";>
scheme@(guile-user)> (car (origin-visits $3))
$4 = #<<visit> date: #<date nanosecond: 490956 second: 6 minute: 45 hour: 14 
day: 29 month: 10 year: 2021 zone-offset: 0> origin: 
"https://github.com/swaywm/sway"; url: 
"https://archive.softwareheritage.org/api/1/origin/https://github.com/swaywm/sway/visit/41/";
 snapshot-url: 
"https://archive.softwareheritage.org/api/1/snapshot/10ba0257e3290ce4504c2413f32b9358d72975d6/";
 status: full number: 41>
scheme@(guile-user)> (define s (visit-snapshot $4))
scheme@(guile-user)> ,pp (map branch-name (snapshot-branches s))
*** output flushed ***
scheme@(guile-user)> (length (snapshot-branches s))
$6 = 1000
scheme@(guile-user)> (filter (lambda (b)
                               (string-prefix? "refs/tags" (branch-name b)))
                             (snapshot-branches s))
$7 = ()
scheme@(guile-user)> ,use(srfi srfi-1)
scheme@(guile-user)> ,pp (take (snapshot-branches s) 10)
$8 = (#<<branch> name: "refs/pull/2715/head" target-type: revision target-url: 
"https://archive.softwareheritage.org/api/1/revision/2f258eff6fd2c89a94caa658c1ea22beb76d728a/";>
 #<<branch> name: "refs/pull/2713/head" target-type: revision target-url: 
"https://archive.softwareheritage.org/api/1/revision/4e4898e90f4d9b721091137a744deac335e73f12/";>
 #<<branch> name: "refs/pull/2712/head" target-type: revision target-url: 
"https://archive.softwareheritage.org/api/1/revision/d129108cddc485299443d0b98c3bdf3f9839aa1c/";>
 #<<branch> name: "refs/pull/271/head" target-type: revision target-url: 
"https://archive.softwareheritage.org/api/1/revision/20cb390323b19dc0c767ba63925def7f51c31044/";>
 #<<branch> name: "refs/pull/2709/head" target-type: revision target-url: 
"https://archive.softwareheritage.org/api/1/revision/426c33f4dc2515867a0d3b04cb865d5cad091d10/";>
 #<<branch> name: "refs/pull/2708/head" target-type: revision target-url: 
"https://archive.softwareheritage.org/api/1/revision/b1a0e95e8e6ecf66542cc62e6109949de59afb5e/";>
 #<<branch> name: "refs/pull/2704/head" target-type: revision target-url: 
"https://archive.softwareheritage.org/api/1/revision/6194a445d3b10e8afc968712faccdd1d127a8beb/";>
 #<<branch> name: "refs/pull/2703/head" target-type: revision target-url: 
"https://archive.softwareheritage.org/api/1/revision/f16529e2588f5e71d6777f4c06dfb58b29308cd0/";>
 #<<branch> name: "refs/pull/2701/head" target-type: revision target-url: 
"https://archive.softwareheritage.org/api/1/revision/baeb28ea6230ef9aa409ee52abe208720120e45c/";>
 #<<branch> name: "refs/pull/270/head" target-type: revision target-url: 
"https://archive.softwareheritage.org/api/1/revision/a32cbb52ce81ee38d2928ba873ff7fc182df8393/";>)

This snapshot has more than 1,000 branches, mostly ‘refs/pull’ branches.
But by default, the endpoint used by ‘visit-snapshot’ only returns the
first 1,000 branches, and then it’s up to the caller to use the
pagination mechanism.

It’s not implemented though!  It turns out the ‘refs/tags’ “branches”
were not among the first thousand branches, so the code incorrectly
thinks that the tag is missing.

The solution is to implement pagination (yuk!), or to use an endpoint to
look up a branch by name instead of using ‘snapshot-branches’ (is there
such an endpoint?).
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Ludo’.