internal/labels: save assigned categories in DB

When the labeler assigns labels to an issue, store the category
names in the DB.

We store the categories instead of the labels because we control them,
so we can ensure that they don't change over time or across projects.

For #64.

Change-Id: I857d5ebbc0c761c0c59b4a3ab7ef203278bd8384
Reviewed-on: https://go-review.googlesource.com/c/oscar/+/639015
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>

internal/labels/labeler.go

@@ -23,6 +23,9 @@ import (
 )
 
 // A Labeler labels GitHub issues.
+// It uses the following database keys:
+// - ["labels.Labeler"] for the action log.
+// - ["labels.Categories", Project, Issue] to record the categories assigned to an issue.
 type Labeler struct {
 	slog        *slog.Logger
 	db          storage.DB
@@ -104,8 +107,9 @@ func (l *Labeler) SkipAuthor(author string) {
 
 // An action has all the information needed to label a GitHub issue.
 type action struct {
-	Issue     *github.Issue
-	NewLabels []string // labels to add
+	Issue      *github.Issue
+	Categories []string // the names of the categories corresponding to the labels
+	NewLabels  []string // labels to add
 }
 
 // result is the result of apply an action.
@@ -199,8 +203,9 @@ func (l *Labeler) logLabelIssue(ctx context.Context, e *github.Event) (advance b
 	}
 
 	act := &action{
-		Issue:     issue,
-		NewLabels: []string{cat.Label},
+		Issue:      issue,
+		Categories: []string{cat.Name},
+		NewLabels:  []string{cat.Label},
 	}
 	l.logAction(l.db, logKey(e), storage.JSON(act), l.requireApproval)
 	return true, nil
@@ -336,6 +341,7 @@ func (l *Labeler) runAction(ctx context.Context, a *action) (*result, error) {
 	if err != nil {
 		return nil, fmt.Errorf("Labeler: edit %s: %w", a.Issue.URL, err)
 	}
+	l.setCategories(a.Issue, a.Categories)
 	return &result{URL: issue.URL}, nil
 }
 
@@ -344,3 +350,28 @@ func (l *Labeler) runAction(ctx context.Context, a *action) (*result, error) {
 func logKey(e *github.Event) []byte {
 	return ordered.Encode(e.Project, e.Issue)
 }
+
+// Latest returns the latest known DBTime marked old by the Poster's Watcher.
+func (l *Labeler) Latest() timed.DBTime {
+	return l.watcher.Latest()
+}
+
+func (l *Labeler) setCategories(i *github.Issue, cats []string) {
+	l.db.Set(categoriesKey(i.Project(), i.Number), []byte(strings.Join(cats, ",")))
+}
+
+// Categories returns the list of categories that the Labeler associated with the given issue.
+// If there is no association, it returns nil, false.
+func (l *Labeler) Categories(project string, issueNumber int64) ([]string, bool) {
+	catstr, ok := l.db.Get(categoriesKey(project, issueNumber))
+	if !ok {
+		return nil, false
+	}
+	return strings.Split(string(catstr), ","), true
+}
+
+const categoriesPrefix = "labels.Categories"
+
+func categoriesKey(project string, num int64) []byte {
+	return ordered.Encode(categoriesPrefix, project, num)
+}

internal/labels/labeler_test.go

@@ -140,3 +140,27 @@ func TestRun(t *testing.T) {
 		t.Fatal("not enough edits")
 	}
 }
+
+func TestCategories(t *testing.T) {
+	const project = "golang/go"
+	lg := testutil.Slogger(t)
+	db := storage.MemDB()
+	gh := github.New(lg, db, nil, nil)
+	lab := New(lg, db, gh, nil, "test")
+	issue := &github.Issue{
+		URL:    "https://api.github.com/repos/my/project/whatever",
+		Number: 123,
+	}
+	cats := []string{"bug", "incomplete"}
+	lab.setCategories(issue, cats)
+	if _, ok := lab.Categories("my/project", 1); ok {
+		t.Error("found, but shouldn't have")
+	}
+	got, ok := lab.Categories("my/project", 123)
+	if !ok {
+		t.Fatal("not found, but should have")
+	}
+	if !slices.Equal(got, cats) {
+		t.Errorf("got %v, want %v", got, cats)
+	}
+}