fix: cloud release trace & lake build :release errors (#3248)

Fixes a bug with Lake cloud releases where a cloud release would produce
a different trace if the package was the root of the workspace versus a
dependency. Also, an explicit fetch of a cloud release (e.g., via `lake
build :release`) will now error out with a non-zero exit code if it
fails to find, download, and unpack a release.

src/lake/Lake/Build/Job.lean

@@ -21,6 +21,9 @@ abbrev ResultM := OptionIO
 
 namespace Job
 
+@[inline] def try? (self : Job α) : Job (Option α) := do
+  some <$> self.run
+
 @[inline] def nil : Job Unit :=
  pure ()
 
@@ -62,6 +65,11 @@ namespace BuildJob
 
 instance : Pure BuildJob := ⟨BuildJob.pure⟩
 
+@[inline] def try? (self : BuildJob α) : BuildJob (Option α) :=
+  mk <| self.toJob.map fun
+    | none => some (none, nilTrace)
+    | some (a, t) => some (some a, t)
+
 @[inline] protected def map (f : α → β) (self : BuildJob α) : BuildJob β :=
   mk <| (fun (a,t) => (f a,t)) <$> self.toJob
 
@@ -88,6 +96,9 @@ instance : Await BuildJob ResultM := ⟨BuildJob.await⟩
 @[inline] def materialize (self : BuildJob α) : ResultM Unit :=
   discard <| await self.toJob
 
+def add (t1 : BuildJob α) (t2 : BuildJob β) : BaseIO (BuildJob α) :=
+  mk <$> seqLeftAsync t1.toJob t2.toJob
+
 def mix (t1 : BuildJob α) (t2 : BuildJob β) : BaseIO (BuildJob Unit) :=
   mk <$> seqWithAsync (fun (_,t) (_,t') => ((), mixTrace t t')) t1.toJob t2.toJob
 

src/lake/Lake/Build/Package.lean

@@ -35,7 +35,7 @@ def Package.recBuildExtraDepTargets (self : Package) : IndexBuildM (BuildJob Uni
     job ← job.mix <| ← dep.extraDep.fetch
   -- Fetch pre-built release if desired and this package is a dependency
   if self.name ≠ (← getWorkspace).root.name ∧ self.preferReleaseBuild then
-    job ← job.mix <| ← self.release.fetch
+    job ← job.add (← self.release.fetch).try?
   -- Build this package's extra dep targets
   for target in self.extraDepTargets do
     job ← job.mix <| ← self.fetchTargetJob target
@@ -49,28 +49,23 @@ def Package.extraDepFacetConfig : PackageFacetConfig extraDepFacet :=
 def Package.fetchRelease (self : Package) : SchedulerM (BuildJob Unit) := Job.async do
   let repo := GitRepo.mk self.dir
   let repoUrl? := self.releaseRepo? <|> self.remoteUrl?
-  let some repoUrl := repoUrl? <|> (← repo.getFilteredRemoteUrl?) | do
-    logWarning <| s!"{self.name}: wanted prebuilt release, " ++
+  let some repoUrl := repoUrl? <|> (← repo.getFilteredRemoteUrl?)
+    | error <| s!"{self.name}: wanted prebuilt release, " ++
       "but package's repository URL was not known; it may need to set `releaseRepo?`"
-    return ((), .nil)
-  let some tag ← repo.findTag? | do
-    logWarning <| s!"{self.name}: wanted prebuilt release, " ++
+  let some tag ← repo.findTag?
+    | error <| s!"{self.name}: wanted prebuilt release, " ++
       "but could not find an associated tag for the package's revision"
-    return ((), .nil)
   let url := s!"{repoUrl}/releases/download/{tag}/{self.buildArchive}"
   let logName := s!"{self.name}/{tag}/{self.buildArchive}"
-  try
-    let depTrace := Hash.ofString url
-    let traceFile := FilePath.mk <| self.buildArchiveFile.toString ++ ".trace"
-    let upToDate ← buildUnlessUpToDate' self.buildArchiveFile depTrace traceFile do
-      logStep s!"Downloading {self.name} cloud release"
-      download logName url self.buildArchiveFile
-    unless upToDate && (← self.buildDir.pathExists) do
-      logStep s!"Unpacking {self.name} cloud release"
-      untar logName self.buildArchiveFile self.buildDir
-    return ((), .nil)
-  else
-    return ((), .nil)
+  let depTrace := Hash.ofString url
+  let traceFile := FilePath.mk <| self.buildArchiveFile.toString ++ ".trace"
+  let upToDate ← buildUnlessUpToDate' self.buildArchiveFile depTrace traceFile do
+    logStep s!"Downloading {self.name} cloud release"
+    download logName url self.buildArchiveFile
+  unless upToDate && (← self.buildDir.pathExists) do
+    logStep s!"Unpacking {self.name} cloud release"
+    untar logName self.buildArchiveFile self.buildDir
+  return ((), .nil)
 
 /-- The `PackageFacetConfig` for the builtin `releaseFacet`. -/
 def Package.releaseFacetConfig : PackageFacetConfig releaseFacet :=