Leave a module out of a walk when its check built it the same as what runs (hq issue 721)

A one-sentence change in a package mesh-builder imports but never reaches moved
build-agent. A merge check now compares each module it builds with the build the
mesh holds, the whole image without file times, labels or creation time, and a
walk is cut without a module every check of its pull requests found the same,
while the mesh still holds that build. A comparison that fails moves the module
as before.

cmd/mesh-controller/same_program_test.go

@@ -0,0 +1,67 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/novox/mesh-controller/internal/inventory"
+	"github.com/novox/mesh-controller/internal/link"
+)
+
+// TestAWalkLeavesOutAModuleWhoseProgramDidNotChange is novox/hq issue 721: mesh-controller #335 changed one sentence
+// that mesh-builder never reaches; its check found build-agent the same as the build the mesh holds, so the walk moves
+// mesh-controller alone and says build-agent is unchanged.
+func TestAWalkLeavesOutAModuleWhoseProgramDidNotChange(t *testing.T) {
+	pull := link.PullRef{Owner: "novox", Repo: "mesh-controller", Number: 335}
+	head := "34050dc6aaaabbbbccccdddd"
+	aPlan := func() *inventory.Plan {
+		return &inventory.Plan{Tiers: [][]string{{"mesh-controller", "build-agent"}},
+			Modules: map[string]*inventory.PlanModule{"mesh-controller": {}, "build-agent": {}},
+			Delivery: &inventory.PlanDelivery{Merges: []inventory.PlanMerge{{Repository: "novox/mesh-controller",
+				Commit: "c2ec0a60", Number: 335, Head: head}}}}
+	}
+	held := map[string]string{"build-agent/agent": "store/build-agent@sha256:aaaa",
+		"mesh-controller/controller": "store/mesh-controller@sha256:cccc"}
+	builds := []link.CheckedBuild{
+		{Pull: pull, Head: head[:12], Built: link.CheckBuilt{Module: "build-agent", Key: "k1",
+			Made:   []link.MadeArtifact{{Name: "agent", Kind: "image", Reference: "scratch/build-agent@sha256:bbbb"}},
+			Same:   "unchanged: its program is the same as running build agent aaaa",
+			SameAs: map[string]string{"agent": "10.0.0.1:5000/build-agent@sha256:aaaa"}}},
+		{Pull: pull, Head: head[:12], Built: link.CheckBuilt{Module: "mesh-controller", Key: "k2",
+			Made: []link.MadeArtifact{{Name: "controller", Kind: "image", Reference: "scratch/mesh-controller@sha256:dddd"}}}},
+	}
+
+	p := aPlan()
+	same := sameAsRunning(p, builds, held)
+	if len(same) != 1 || same["build-agent"] == "" {
+		t.Fatalf("the walk leaves out %v, want build-agent alone", same)
+	}
+	withhold(p, []string{"build-agent"}, nil)
+	if len(p.Tiers) != 1 || len(p.Tiers[0]) != 1 || p.Tiers[0][0] != "mesh-controller" {
+		t.Fatalf("the walk moves %v, want mesh-controller alone", p.Tiers)
+	}
+
+	// **The held build moved since the check**: what it was compared with no longer runs.
+	moved := map[string]string{"build-agent/agent": "store/build-agent@sha256:eeee"}
+	if same := sameAsRunning(aPlan(), builds, moved); len(same) != 0 {
+		t.Fatalf("a module compared with a build the mesh no longer holds is left out: %v", same)
+	}
+	// **A check of another head** says nothing of this merge.
+	other := aPlan()
+	other.Delivery.Merges[0].Head = "ffffffffffffffff"
+	if same := sameAsRunning(other, builds, held); len(same) != 0 {
+		t.Fatalf("a check of another head left out %v", same)
+	}
+	// **Another pull request the walk answers** that did not find it the same leaves it in.
+	two := aPlan()
+	two.Delivery.Merges = append(two.Delivery.Merges, inventory.PlanMerge{Repository: "novox/mesh-catalog",
+		Commit: "1234", Number: 9, Head: "abcdefabcdefabcdef"})
+	if same := sameAsRunning(two, builds, held); len(same) != 0 {
+		t.Fatalf("a module another merge moves is left out: %v", same)
+	}
+	// **A merge with no pull request** leaves the walk as it is.
+	direct := aPlan()
+	direct.Delivery.Merges[0].Number = 0
+	if same := sameAsRunning(direct, builds, held); len(same) != 0 {
+		t.Fatalf("a walk answering a merge without a pull request left out %v", same)
+	}
+}