mesh-build-go: give each ask a cache layer in its workspace, so what its vet compiles its unit tests and integration level find compiled (issue 1921, try speed S2)

modules/mesh-build-go/cmd/mesh-build-go/isolate.go

@@ -29,21 +29,30 @@ func (m *Module) caches() []string {
 }
 
 // isolation is how a run step of the workspace is shut off: the workspace (its tree, its siblings, its run directories,
-// its packed artifacts) read-write, the caches beneath a throwaway layer unless write, and an environment of a PATH and
+// its packed artifacts) read-write, the caches beneath the ask's own layer unless write, and an environment of a PATH and
 // a locale alone (the step's HOME is its own, inside its /tmp).
 func (m *Module) isolation(workspace string, write bool) buildstep.Isolation {
 	path := os.Getenv("PATH")
 	if path == "" {
 		path = defaultPath
 	}
-	return buildstep.Isolation{
+	iso := buildstep.Isolation{
 		Workspace:   filepath.Join(m.Work, workspace),
 		Caches:      m.caches(),
 		WriteCaches: write,
 		Env:         []string{"PATH=" + path, "LC_ALL=C"},
 	}
+	if !write {
+		// What one command of the ask compiles is kept for its later commands (the vet, the unit tests, the integration
+		// level's compile), in the workspace and gone with it (issue 1921, try speed S2).
+		iso.CacheLayer = filepath.Join(iso.Workspace, cacheLayerDir)
+	}
+	return iso
 }
 
+// cacheLayerDir is the directory in a workspace's root where an ask keeps what its commands wrote into the caches.
+const cacheLayerDir = "cachelayer"
+
 // stepRunner is the runner of a run step of the workspace: buildstep.Isolated over m.Run, so every command it runs is
 // shut off; write is true for a trunk build alone (the shared caches are written by trunk builds only). Inside is the
 // integration level's own process, already running shut off (level.go): it runs its commands as they are.

modules/mesh-build-go/cmd/mesh-build-go/isolate_test.go

@@ -20,6 +20,7 @@ import (
 type shutOff struct {
 	flags                    []string
 	binds, roBinds, overlays []string
+	uppers                   map[string]string // the writable layer each --overlay gives a cache: cache -> upper
 	env                      []string
 	command                  string
 	chdir                    string
@@ -27,7 +28,7 @@ type shutOff struct {
 
 // bwrapArity is how many words each bubblewrap option the SDK writes takes.
 var bwrapArity = map[string]int{"--unshare-all": 0, "--die-with-parent": 0, "--new-session": 0, "--clearenv": 0,
-	"--proc": 1, "--dev": 1, "--tmpfs": 1, "--dir": 1, "--chdir": 1, "--overlay-src": 1, "--tmp-overlay": 1,
+	"--proc": 1, "--dev": 1, "--tmpfs": 1, "--dir": 1, "--chdir": 1, "--overlay-src": 1, "--tmp-overlay": 1, "--overlay": 3,
 	"--ro-bind": 2, "--ro-bind-try": 2, "--bind": 2, "--symlink": 2, "--setenv": 2}
 
 // throughBubblewrap is the fake runner of a step's tests: a bubblewrap command is read back (recorded in seen) and its
@@ -56,6 +57,11 @@ func throughBubblewrap(t *testing.T, run forgekey.Runner, seen *[]shutOff) forge
 				s.roBinds = append(s.roBinds, args[i+1])
 			case "--overlay-src":
 				s.overlays = append(s.overlays, args[i+1])
+			case "--overlay":
+				if s.uppers == nil {
+					s.uppers = map[string]string{}
+				}
+				s.uppers[args[i+3]] = args[i+1]
 			case "--setenv":
 				s.env = append(s.env, args[i+1]+"="+args[i+2])
 			case "--chdir":
@@ -105,6 +111,9 @@ func checkShutOff(t *testing.T, m *Module, s shutOff, write bool) {
 			t.Errorf("a trunk build's %s does not write the shared cache %s (bound %v, layered %v)", s.command, c, bound, layered)
 		case !write && (bound || !layered):
 			t.Errorf("%s may write the shared cache %s (bound %v, layered %v): only a trunk build does", s.command, c, bound, layered)
+		case !write && !strings.HasPrefix(s.uppers[c], filepath.Join(m.Work, "ws1", "cachelayer")+"/"):
+			// 1921/S2: what one command of the ask compiles is kept for its later commands, in the workspace
+			t.Errorf("%s writes the cache %s into %q, not the ask's cache layer in its workspace", s.command, c, s.uppers[c])
 		}
 	}
 	if want := filepath.Join(m.Work, "ws1"); !slices.Contains(s.binds, want) {

modules/mesh-build-go/go.mod

@@ -3,7 +3,7 @@ module meshbuildgo
 go 1.26.0
 
 require (
-	git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261024214154-bc16740feb0d
+	git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261024225846-cb548a6a588c
 	github.com/distribution/distribution/v3 v3.1.2
 	github.com/nats-io/nats-server/v2 v2.11.17
 	github.com/nats-io/nats.go v1.54.0

modules/mesh-build-go/go.sum

@@ -1,5 +1,7 @@
 git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261024214154-bc16740feb0d h1:oJREw0ggKqJWJ5DEISSL0i2ZC5XqdXAidxo9NJ74TCc=
 git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261024214154-bc16740feb0d/go.mod h1:ouERNpZizzwZ0HLEtAypsY9FR20FyUgUYRni6J7kVCY=
+git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261024225846-cb548a6a588c h1:GWHP9ozfkFXHVEL2gE4Xa5kc5e8uPO+UL9+mau6iaIs=
+git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261024225846-cb548a6a588c/go.mod h1:ouERNpZizzwZ0HLEtAypsY9FR20FyUgUYRni6J7kVCY=
 github.com/alicebob/miniredis/v2 v2.35.0 h1:QwLphYqCEAo1eu1TqPRN2jgVMPBweeQcR21jeqDCONI=
 github.com/alicebob/miniredis/v2 v2.35.0/go.mod h1:TcL7YfarKPGDAthEtl5NBeHZfeUQj6OXMm/+iu5cLMM=
 github.com/antithesishq/antithesis-sdk-go v0.7.0-default-no-op h1:Z/MZK75wC/NSrkgqeNIa7jexam9uWzhLmFTSCPI/kn0=