chore: improve build deadline code (#19203)

- Adds/improves a lot of comments to make the autostop calculation code
clearer
- Changes the behavior of the enterprise template schedule store to
match the behavior of the workspace TTL endpoint when the new TTL is
zero
- Fixes a bug in the workspace TTL endpoint where it could unset the
build deadline, even though a max_deadline was specified
- Adds a new constraint to the workspace_builds table that enforces the
deadline is non-zero and below the max_deadline if it is set
- Adds CHECK constraint enum generation to scripts/dbgen, used for
testing the above constraint
- Adds Dean and Danielle as CODEOWNERS for the autostop calculation code

coderd/workspaces.go

@@ -45,8 +45,8 @@ import (
 )
 
 var (
-	ttlMin = time.Minute //nolint:revive // min here means 'minimum' not 'minutes'
-	ttlMax = 30 * 24 * time.Hour
+	ttlMinimum = time.Minute
+	ttlMaximum = 30 * 24 * time.Hour
 
 	errTTLMin              = xerrors.New("time until shutdown must be at least one minute")
 	errTTLMax              = xerrors.New("time until shutdown must be less than 30 days")
@@ -1190,8 +1190,22 @@ func (api *API) putWorkspaceTTL(rw http.ResponseWriter, r *http.Request) {
 
 			if build.Transition == database.WorkspaceTransitionStart {
 				if err = s.UpdateWorkspaceBuildDeadlineByID(ctx, database.UpdateWorkspaceBuildDeadlineByIDParams{
-					ID:          build.ID,
-					Deadline:    time.Time{},
+					ID: build.ID,
+					// Use the max_deadline as the new build deadline. It will
+					// either be zero (our target), or a non-zero value that we
+					// need to abide by anyway due to template policy.
+					//
+					// Previously, we would always set the deadline to zero,
+					// which was incorrect behavior. When max_deadline is
+					// non-zero, deadline must be set to a non-zero value that
+					// is less than max_deadline.
+					//
+					// Disabling TTL autostop (at a workspace or template level)
+					// does not trump the template's autostop requirement.
+					//
+					// Refer to the comments on schedule.CalculateAutostop for
+					// more information.
+					Deadline:    build.MaxDeadline,
 					MaxDeadline: build.MaxDeadline,
 					UpdatedAt:   dbtime.Time(api.Clock.Now()),
 				}); err != nil {
@@ -2391,11 +2405,11 @@ func validWorkspaceTTLMillis(millis *int64, templateDefault time.Duration) (sql.
 
 	dur := time.Duration(*millis) * time.Millisecond
 	truncated := dur.Truncate(time.Minute)
-	if truncated < ttlMin {
+	if truncated < ttlMinimum {
 		return sql.NullInt64{}, errTTLMin
 	}
 
-	if truncated > ttlMax {
+	if truncated > ttlMaximum {
 		return sql.NullInt64{}, errTTLMax
 	}