mesh-controller/cmd/mesh-controller/same_program.go

package main

import (
	"context"
	"fmt"
	"slices"
	"sort"
	"strings"

	"github.com/novox/mesh-controller/internal/inventory"
)

// **A module moves only when its source changes** (novox/hq issue 721; from R4e by its fingerprint, ADR 0453 §6, ADR
// 0499; issue 1851, A9). A walk is cut without a module whose fingerprint at the commit the walk carries is the
// fingerprint of the build the mesh holds of it, and says so among the modules it left unchanged: a merge of a file no
// module reads moves nothing. A build the mesh holds of the old form (build-agent's `src1:`) has no fingerprint to
// compare: the module stays in the walk, and the rule of the standing build (equal digests, no move) judges it once its
// key is taken.

// sameByFingerprint are the modules whose fingerprint now (`src2:`, the indexer's trunk value at the walk's commit) is
// the fingerprint of the build the mesh holds, each with why; one whose either is unknown, or of the old form, is not.
func sameByFingerprint(now, held map[string]string) map[string]string {
	out := map[string]string{}
	for m, fp := range now {
		if strings.HasPrefix(fp, "src2:") && held[m] == fp {
			out[m] = fmt.Sprintf("unchanged: its fingerprint %s is the build the mesh holds", short(fp))
		}
	}
	if len(out) == 0 {
		return nil
	}
	return out
}

// heldFingerprint is the source fingerprint of the build the mesh holds of a module: the newest build of the commit
// it is registered at.
func heldFingerprint(ctx context.Context, inv *inventory.Inventory, module string) (string, error) {
	src, err := inv.SourceOf(ctx, module)
	if err != nil {
		return "", err
	}
	fps, err := inv.BuildSourceFingerprints(ctx, module)
	if err != nil {
		return "", err
	}
	for commit, fp := range fps {
		if sameCommitID(commit, src.BuiltFrom) {
			return fp, nil
		}
	}
	return "", nil
}

// leaveSameAsRunning takes from a walk being cut every module whose fingerprint is unchanged (sameByFingerprint), and
// every dependent in the walk only for one of those (withDependentsOf): what was taken, with why. **Anything not read
// leaves the walk as it was**, said.
func leaveSameAsRunning(ctx context.Context, inv *inventory.Inventory, plan *inventory.Plan, moved []string,
	edges []inventory.Edge) map[string]string {
	if len(plan.Modules) == 0 {
		return nil
	}
	entries, err := inv.Catalogued(ctx)
	if err != nil {
		fmt.Printf("  the catalogue could not be read, so every module moves: %v\n", err)
		// empty-on-error: said above; nothing left out of the walk is the safe answer, every module moves as before
		return nil
	}
	keys, closeKeys, err := openPlanKeys()
	if err != nil {
		fmt.Printf("  the indexer's fingerprints could not be read, so every module moves: %v\n", err)
		// empty-on-error: said above; nothing left out of the walk is the safe answer, every module moves as before
		return nil
	}
	defer closeKeys()
	byName := map[string]inventory.Entry{}
	for _, e := range entries {
		byName[e.Manifest.Module] = e
	}
	now, held := map[string]string{}, map[string]string{}
	for m := range plan.Modules {
		e, known := byName[m]
		if !known || isBuildersOwn(m) {
			continue
		}
		v, err := keys.ModuleAt(ctx, m, plan.CommitOn(e.Source.Repository, followedBranch(e.Source.Ref)))
		if err != nil || v.FP2 == "" {
			continue // not written yet, or none: the module moves, and its key is waited for in the walk
		}
		fp, err := heldFingerprint(ctx, inv, m)
		if err != nil {
			continue
		}
		now[m], held[m] = v.FP2, fp
	}
	same := withDependentsOf(sameByFingerprint(now, held), plan, moved, edges)
	if len(same) == 0 {
		return nil
	}
	names := make([]string, 0, len(same))
	for n := range same {
		names = append(names, n)
	}
	sort.Strings(names)
	withhold(plan, names, nil)
	for _, n := range names {
		fmt.Printf("  %s left out: %s\n", n, same[n])
	}
	return same
}

// withDependentsOf adds to the modules found the same every module of the walk that is in it only as a dependent of
// one of them (novox/hq ADR 0267 rule 3): **a dependent is left out when its base comes out the same**, since the
// base it stands on stays the build the mesh holds. A module a merge moves itself, or a dependent of a base that
// still moves, stays. moved are the modules the walk's merges move; edges the graph the walk was planned along.
func withDependentsOf(same map[string]string, plan *inventory.Plan, moved []string, edges []inventory.Edge) map[string]string {
	if len(same) == 0 {
		return same
	}
	var still []string
	for _, n := range moved {
		if same[n] == "" {
			still = append(still, n)
		}
	}
	keep := map[string]bool{}
	for _, n := range reachableFrom(still, edges) {
		keep[n] = true
	}
	// Until nothing more is found: a dependent of a dependent left out is left out too.
	for grew := true; grew; {
		grew = false
		for n := range plan.Modules {
			if keep[n] || same[n] != "" {
				continue
			}
			var bases []string
			for _, e := range edges {
				ordering := e.Kind == inventory.EdgeBuiltBy || e.Kind == inventory.EdgeWorkerOf ||
					e.Kind == inventory.EdgePackages || e.Kind == edgeChangeOrder
				if !ordering && e.From == n && same[e.To] != "" && !slices.Contains(bases, e.To) {
					bases = append(bases, e.To)
				}
			}
			sort.Strings(bases)
			if len(bases) == 0 {
				// In the walk for no base found the same: whatever brought it in is not said here, so it moves.
				continue
			}
			same[n] = "unchanged: it is in the walk only for " + strings.Join(bases, ", ") +
				", which came out the same as the build the mesh holds (ADR 0267 rule 3)"
			grew = true
		}
	}
	return same
}