Merge pull request 'mesh-build-go: a merge preview names a path and a path inside it (mesh-contracts' go), and a step's cause keeps the module Go could not find (issue 1966)' (#613) from fix/buildstep-preview into main

Claude-Session: https://claude.ai/code/session_01JG73KJNrH5EgFXMKKYSrig

modules/mesh-build-go/buildstep/trees.go

@@ -82,18 +82,20 @@ func narrow(ctx context.Context, run forgekey.Runner, env []string, dir, commit,
 	for i, p := range paths {
 		full[i] = path.Join(mdir, p)
 	}
-	r := run(ctx, env, "git", append([]string{"-C", dir, "ls-tree", "-z", commit, "--"}, full...)...)
-	if r.Status != 0 || r.Err != "" {
-		return fmt.Errorf("git ls-tree %s of the module %s: %s", commit, mdir, forgekey.Said(r.Err+"\n"+r.Stderr))
-	}
 	objects := map[string]string{}
-	for _, l := range strings.Split(r.Stdout, "\x00") {
-		meta, name, ok := strings.Cut(l, "\t")
-		fields := strings.Fields(meta)
-		if !ok || len(fields) != 3 {
-			continue
+	for _, round := range unnested(full) {
+		r := run(ctx, env, "git", append([]string{"-C", dir, "ls-tree", "-z", commit, "--"}, round...)...)
+		if r.Status != 0 || r.Err != "" {
+			return fmt.Errorf("git ls-tree %s of the module %s: %s", commit, mdir, forgekey.Said(r.Err+"\n"+r.Stderr))
+		}
+		for _, l := range strings.Split(r.Stdout, "\x00") {
+			meta, name, ok := strings.Cut(l, "\t")
+			fields := strings.Fields(meta)
+			if !ok || len(fields) != 3 {
+				continue
+			}
+			objects[name] = fields[2]
 		}
-		objects[name] = fields[2]
 	}
 	mt.Paths = map[string]string{}
 	for i, p := range paths {
@@ -106,4 +108,35 @@ func narrow(ctx context.Context, run forgekey.Runner, env []string, dir, commit,
 	return nil
 }
 
+// unnested splits paths into rounds of one git ls-tree each, none of whose paths lies inside another of its round: given
+// "go" and "go/seats/x" together, git ls-tree descends into go and lists its children instead of go itself, so the
+// object of go is missing from its answer (issue 1966: mesh-contracts' manifest names both). Usually one round; the
+// order of paths is kept within a round.
+func unnested(paths []string) [][]string {
+	var rounds [][]string
+	for _, p := range paths {
+		placed := false
+		for i, round := range rounds {
+			if !nestsWithAny(p, round) {
+				rounds[i] = append(round, p)
+				placed = true
+				break
+			}
+		}
+		if !placed {
+			rounds = append(rounds, []string{p})
+		}
+	}
+	return rounds
+}
+
+func nestsWithAny(p string, round []string) bool {
+	for _, q := range round {
+		if p == q || strings.HasPrefix(p, q+"/") || strings.HasPrefix(q, p+"/") || p == "." || q == "." {
+			return true
+		}
+	}
+	return false
+}
+
 func sha256Hex(b []byte) string { h := sha256.Sum256(b); return hex.EncodeToString(h[:]) }

modules/mesh-build-go/buildstep/trees_integration_test.go

@@ -62,4 +62,16 @@ func TestAGoOnlyCommitLeavesTheNamedObjectsEqualOnRealGit(t *testing.T) {
 	if src["."].Paths["src"] != realGit(t, repo, "rev-parse", "HEAD:src") {
 		t.Fatalf("the object of src is %s, git says %s", src["."].Paths["src"], realGit(t, repo, "rev-parse", "HEAD:src"))
 	}
+
+	// A manifest naming a path and a path inside it (mesh-contracts' "go" and "go/seats/meshvault"; issue 1966): each
+	// gets its own object, not git ls-tree's listing of the outer one's children.
+	writeFile(t, repo, "nested/module.json", `{"module":"nested","version":"1","build":{"artifacts":[`+
+		`{"name":"go","kind":"package","language":"go","paths":["go"]},`+
+		`{"name":"go-seat","kind":"package","language":"go","paths":["go/seats/a"]}]}}`)
+	writeFile(t, repo, "nested/go/go.mod", "module x\n")
+	writeFile(t, repo, "nested/go/seats/a/a.go", "package a\n")
+	nested := trees(commit("nested"))["nested"]
+	if nested.Paths["go"] != realGit(t, repo, "rev-parse", "HEAD:nested/go") || nested.Paths["go/seats/a"] != realGit(t, repo, "rev-parse", "HEAD:nested/go/seats/a") {
+		t.Fatalf("a path and a path inside it: %v", nested.Paths)
+	}
 }

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

@@ -97,9 +97,10 @@ func (m *Module) candidate(ctx context.Context, workspace string) (string, error
 // compileError is the first line of the compiler's output that says an error: not the `# package` heading go build
 // prints above a package's errors, nor Go's progress.
 func compileError(out string) string {
-	for _, l := range strings.Split(out, "\n") {
+	lines := strings.Split(out, "\n")
+	for i, l := range lines {
 		if l = strings.TrimSpace(l); l != "" && !strings.HasPrefix(l, "#") && !strings.HasPrefix(l, "go: downloading ") {
-			return l
+			return withContinuation(l, lines[i+1:])
 		}
 	}
 	return firstLine(out)

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

@@ -351,15 +351,33 @@ func (m *Module) now() time.Time { return m.clock() }
 // causeLine is the first line of a go command's output that says something other than Go's own progress: `go:
 // downloading ...` comes first when Go fetches a module, and `# <package>` heads a compile error of go build or go vet
 // (issue 1703: the reason said only the package), and the cause of a failure on a later line.
+//
+// A cause Go writes over several lines keeps its indented continuation lines, joined by a space: a module graph error
+// is "X requires" with the module that fails, and why, on the next line (issue 1966: the composer's reason ended at
+// "requires" and hid "golang.org/x/tools@v0.42.0: module lookup disabled").
 func causeLine(s string) string {
-	for _, l := range strings.Split(s, "\n") {
+	lines := strings.Split(s, "\n")
+	for i, l := range lines {
 		if l = strings.TrimSpace(l); l != "" && !strings.HasPrefix(l, "go: downloading ") && !strings.HasPrefix(l, "# ") {
-			return l
+			return withContinuation(l, lines[i+1:])
 		}
 	}
 	return firstLine(s)
 }
 
+// withContinuation is first with each following line Go indented under it, trimmed and joined by a space.
+func withContinuation(first string, rest []string) string {
+	for _, l := range rest {
+		if !strings.HasPrefix(l, "\t") && !strings.HasPrefix(l, "    ") {
+			break
+		}
+		if l = strings.TrimSpace(l); l != "" {
+			first += " " + l
+		}
+	}
+	return first
+}
+
 func firstLine(s string) string {
 	for _, l := range strings.Split(s, "\n") {
 		if l = strings.TrimSpace(l); l != "" {

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

@@ -309,9 +309,14 @@ func TestCauseLineSkipsProgressAndThePackageHeading(t *testing.T) {
 		"go: downloading x v1\n# git.example/m/cmd\n./main.go:3:2: undefined: y\n": "./main.go:3:2: undefined: y",
 		"\ngo: example.com/x@v1: reading: 404\n":                                   "go: example.com/x@v1: reading: 404",
 		"go: downloading x v1\n":                                                   "go: downloading x v1",
+		// issue 1966: a module graph error goes on, indented, on the next line; a later error is not taken in.
+		"a.go:3:8: x@v1 requires\n\ty@v2: module lookup disabled by GOPROXY=off\nb.go:1:1: other\n": "a.go:3:8: x@v1 requires y@v2: module lookup disabled by GOPROXY=off",
 	} {
 		if got := causeLine(in); got != want {
 			t.Errorf("causeLine(%q) = %q, want %q", in, got, want)
 		}
+		if got := compileError(in); got != want {
+			t.Errorf("compileError(%q) = %q, want %q", in, got, want)
+		}
 	}
 }