eval: matchN buries error about missing required fields

[myitcv]

What version of CUE are you using (cue version)?

$ cue version
cue version v0.0.0-20250109154455-bbb2452ee698

go version go1.23.2
      -buildmode exe
       -compiler gc
  DefaultGODEBUG asynctimerchan=1,gotypesalias=0,httpservecontentkeepheaders=1,tls3des=1,tlskyber=0,x509keypairleaf=0,x509negativeserial=1
     CGO_ENABLED 1
          GOARCH arm64
            GOOS linux
         GOARM64 v8.0
             vcs git
    vcs.revision bbb2452ee698eb6043b0f8a29ef8e71d0f3400f0
        vcs.time 2025-01-09T15:44:55Z
    vcs.modified false
cue.lang.version v0.12.0

Does this issue reproduce with the latest release?

n/a - testing with tip

What did you do?

# case1
! exec cue export x.cue case1.cue
cmp stderr stderr.golden

# case2
! exec cue export x.cue case2.cue
cmp stderr stderr.golden

-- x.cue --
package x

#step: matchN(1, [{
	run!: string
}, {
	uses!: string
}])

#job: {
	steps!: [...#step]
}

let _template = {
	#run!: string
	run:   #run
}

w: #workflow & {
	jobs: test: steps: [
		_template,
	]
}
-- case1.cue --
package x

#workflow: {
	jobs!: [string]: #job
}
-- case2.cue --
package x

#workflow: {
	jobs!: [string]: matchN(1, [#job])
}
-- stderr.golden --
w.jobs.test.steps.0.#run: field is required but not present:
    ./x.cue:14:2
    ./x.cue:20:3
w.jobs.test.steps.0.run: incomplete value string:
    ./x.cue:14:9

What did you expect to see?

Passing test.

What did you see instead?

# case1 (0.013s)
# case2 (0.010s)
> ! exec cue export x.cue case2.cue
[stderr]
w.jobs.test: invalid value {steps:[{#run!:string,run:string}]} (does not satisfy matchN): 0 matched, expected 1:
    ./case2.cue:4:19
    ./case2.cue:4:26
    ./x.cue:19:14
[exit status 1]
> cmp stderr stderr.golden
diff stderr stderr.golden
--- stderr
+++ stderr.golden
@@ -1,4 +1,5 @@
-w.jobs.test: invalid value {steps:[{#run!:string,run:string}]} (does not satisfy matchN): 0 matched, expected 1:
-    ./case2.cue:4:19
-    ./case2.cue:4:26
-    ./x.cue:19:14
+w.jobs.test.steps.0.#run: field is required but not present:
+    ./x.cue:14:2
+    ./x.cue:20:3
+w.jobs.test.steps.0.run: incomplete value string:
+    ./x.cue:14:9

FAIL: /tmp/testscript2944458678/repro.txtar/script.txtar:7: stderr and stderr.golden differ

Note that this appears to be different from https://cuelang.org/issue/3651 because I still see the same behaviour when testing against https://cuelang.org/cl/1206950/1

Note also the only diff between case1 and case2 is the "wrapping" with an additional matchN:

--- case1.cue   2025-01-09 17:36:32.083576069 +0000
+++ case2.cue   2025-01-09 17:36:32.083576069 +0000
@@ -1,5 +1,5 @@
 package x

 #workflow: {
-       jobs!: [string]: #job
+       jobs!: [string]: matchN(1, [#job])
 }

[mpvl]

This is marked as evalv3, but from the test it doesn't appear to be an issue specific to evalv3.

[myitcv]

Let me take a look. For some reason I can't reproduce the original problem that I had (this issue is a much-reduced form of a wider issue).

[myitcv]

I think there must be an element of user error here (i.e. my fault). I haven't managed to replay the sequence of steps that lead to me raising this issue. Specifically, I'm fairly sure I got here because evalv3 failed on the cuelang.org CI setup. But I now can't reproduce the problem. So I'll close this issue for now, and re-open if required.