Read a new module's directory as its own, not as shared code (hq issue 252)

A merge adding a module the mesh has not registered rebuilt every module
built from the repository. A path under a directory known to hold modules
belongs to that module when its module.json is among the changed files.

cmd/mesh-controller/order_test.go

@@ -147,6 +147,14 @@ func TestAMergeRebuildsTheModulesItChanged(t *testing.T) {
 		{"a module the mesh does not hold", merge([]string{"modules/plex/index.ts"}, false), ""},
 		{"nothing said about the files", merge(nil, false), "gitea,keycloak"},
 		{"more files than were listed", merge([]string{"modules/gitea/index.ts"}, true), "gitea,keycloak"},
+		// novox/hq issue 252: a module the mesh has never registered is still a module, when the merge
+		// shows it is one — and a directory that may be shared code is still shared.
+		{"a new module beside a held one", merge([]string{"modules/gitea/x", "modules/newmod/module.json"}, false), "gitea"},
+		{"a new module's other files", merge([]string{"modules/newmod/index.ts", "modules/newmod/module.json"}, false), ""},
+		{"a module removed", merge([]string{"modules/gone/module.json"}, false), ""},
+		{"a directory with no manifest", merge([]string{"modules/lib/x.go"}, false), "gitea,keycloak"},
+		{"a file directly among the modules", merge([]string{"modules/README.md"}, false), "gitea,keycloak"},
+		{"the root's files still", merge([]string{"tsconfig.json"}, false), "gitea,keycloak"},
 	} {
 		if got := named(whatTheMergeTouched(candidates, known, c.m)); got != c.want {
 			t.Errorf("%s: rebuilt %q, wanted %q", c.what, got, c.want)

cmd/mesh-controller/upgrades.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"flag"
 	"fmt"
+	"path"
 	"regexp"
 	"strings"
 	"time"
@@ -423,25 +424,45 @@ func lastLookAt(entries []inventory.Entry, m link.SourceMoved) time.Time {
 //
 // A change inside *another* module's directory is that module's business and not this one's, even
 // when the mesh does not hold that module: `known` is every module this repository is known to hold,
-// whatever branch it was registered from. That is also the limit of this — a repository whose shared
-// code sits inside a directory the mesh has never seen a module in reads as shared, and everything
-// is rebuilt. Rebuilding too much is the safe direction: the fault this whole path exists for is a
-// mesh that believes it is current and is not (novox/hq 04-ISSUES/131).
+// whatever branch it was registered from.
+//
+// **And a module the mesh has never seen is still a module** (novox/hq issue 252). A merge adding a
+// new module to the catalogue repository — `modules/newmod/module.json` and its files — read as a
+// change to shared code, because `modules/newmod` was nobody's known directory, and every module
+// built from the repository was rebuilt and rolled out for a module none of them is. So the
+// directories that hold modules are known too: the parents of the known modules' directories
+// (`modules`, never the root). A changed path `<parent>/<name>/…` belongs to the module at
+// `<parent>/<name>` — held or not — and rebuilds nothing else, **provided it is shown to be a
+// module**: its `module.json` is among the changed files (added, changed, or removed with it). A
+// directory under the same parent whose manifest the merge did not touch may as well be a shared
+// library (`modules/lib`), and that is still read as shared. Rebuilding too much remains the safe
+// direction: the fault this whole path exists for is a mesh that believes it is current and is not
+// (novox/hq 04-ISSUES/131). A file at the root, or directly in a parent, is shared as it always was.
 func whatTheMergeTouched(candidates, known []inventory.Entry, m link.SourceMoved) []inventory.Entry {
 	// Nothing said about the files, or not all of them said: everything built from it is affected.
 	if len(m.Paths) == 0 || m.PathsTruncated {
 		return candidates
 	}
 	var dirs []string
+	parents := map[string]bool{}
 	for _, e := range known {
 		if e.Source.Path != "" && sameRepository(e.Source.Repository, m) {
-			dirs = append(dirs, e.Source.Path)
+			dir := strings.Trim(e.Source.Path, "/")
+			dirs = append(dirs, dir)
+			if parent := path.Dir(dir); parent != "." && parent != "/" {
+				parents[parent] = true
+			}
 		}
 	}
+	changed := map[string]bool{}
 	for _, p := range m.Paths {
-		if !insideAny(p, dirs) {
-			return candidates
+		changed[strings.TrimPrefix(p, "/")] = true
+	}
+	for _, p := range m.Paths {
+		if insideAny(p, dirs) || inAModuleOfItsOwn(p, parents, changed) {
+			continue
 		}
+		return candidates
 	}
 	var out []inventory.Entry
 	for _, e := range candidates {
@@ -452,6 +473,28 @@ func whatTheMergeTouched(candidates, known []inventory.Entry, m link.SourceMoved
 	return out
 }
 
+// inAModuleOfItsOwn is whether a changed file is inside a module directory the mesh does not know —
+// `<parent>/<name>/…` under a directory known to hold modules, whose `module.json` the same merge
+// changed (novox/hq issue 252). Such a file is that module's business and nobody else's.
+func inAModuleOfItsOwn(p string, parents, changed map[string]bool) bool {
+	p = strings.TrimPrefix(p, "/")
+	for parent := range parents {
+		rest, under := strings.CutPrefix(p, parent+"/")
+		if !under {
+			continue
+		}
+		name, _, inADirectory := strings.Cut(rest, "/")
+		if !inADirectory || name == "" {
+			// A file directly in the parent — `modules/README.md` — is about all of them.
+			continue
+		}
+		if changed[parent+"/"+name+"/module.json"] {
+			return true
+		}
+	}
+	return false
+}
+
 // inside is whether a changed file is in a directory: that directory itself, or under it.
 func inside(path, dir string) bool {
 	dir = strings.Trim(dir, "/")