internal/postgres: read from imports table

Read from the imports table instead of package_imports, under an
experiment.

Change-Id: Id5b61285325f28a168faeb25651839663269feaf
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/326450
Trust: Jonathan Amsterdam <jba@google.com>
Run-TryBot: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Jamal Carvalho <jamal@golang.org>
Reviewed-by: Julie Qiu <julie@golang.org>

4 files changed, 18 insertions, 5 deletions

diff --git a/internal/experiment.go b/internal/experiment.go
index df31efbb..27d99b0d 100644
--- a/internal/experiment.go
+++ b/internal/experiment.go
@@ -10,6 +10,7 @@ const (
 	ExperimentEnableStdFrontendFetch      = "enable-std-frontend-fetch"
 	ExperimentInsertSymbolSearchDocuments = "insert-symbol-search-documents"
 	ExperimentNewUnitLayout               = "new-unit-layout"
+	ExperimentReadImports                 = "read-imports"
 	ExperimentReadSymbolHistory           = "read-symbol-history"
 	ExperimentSearchGrouping              = "search-grouping"
 	ExperimentSkipInsertSymbols           = "skip-insert-symbols"
@@ -26,6 +27,7 @@ var Experiments = map[string]string{
 	ExperimentEnableStdFrontendFetch:      "Enable frontend fetching for module std.",
 	ExperimentInsertSymbolSearchDocuments: "Insert data into symbol_search_documents.",
 	ExperimentNewUnitLayout:               "Enable the new layout on the unit page.",
+	ExperimentReadImports:                 "Read from imports instead of package_imports.",
 	ExperimentReadSymbolHistory:           "Read data from the symbol_history table.",
 	ExperimentSearchGrouping:              "Group search results.",
 	ExperimentSkipInsertSymbols:           "Don't insert data into symbols tables.",
diff --git a/internal/frontend/unit.go b/internal/frontend/unit.go
index ececd614..c9f70519 100644
--- a/internal/frontend/unit.go
+++ b/internal/frontend/unit.go
@@ -90,8 +90,7 @@ type UnitPage struct {
 	Details interface{}
 }
 
-// serveUnitPage serves a unit page for a path using the paths,
-// modules, documentation, readmes, licenses, and package_imports tables.
+// serveUnitPage serves a unit page for a path.
 func (s *Server) serveUnitPage(ctx context.Context, w http.ResponseWriter, r *http.Request,
 	ds internal.DataSource, info *urlPathInfo) (err error) {
 	defer derrors.Wrap(&err, "serveUnitPage(ctx, w, r, ds, %v)", info)
diff --git a/internal/postgres/unit.go b/internal/postgres/unit.go
index 7c7e9c66..b2528f48 100644
--- a/internal/postgres/unit.go
+++ b/internal/postgres/unit.go
@@ -316,10 +316,17 @@ func (db *DB) getUnitID(ctx context.Context, fullPath, modulePath, resolvedVersi
 func (db *DB) getImports(ctx context.Context, unitID int) (_ []string, err error) {
 	defer derrors.WrapStack(&err, "getImports(ctx, %d)", unitID)
 	defer middleware.ElapsedStat(ctx, "getImports")()
-	return collectStrings(ctx, db.db, `
+	query := `
 		SELECT to_path
 		FROM package_imports
-		WHERE unit_id = $1`, unitID)
+		WHERE unit_id = $1`
+	if experiment.IsActive(ctx, internal.ExperimentReadImports) {
+		query = `
+		SELECT p.path
+		FROM paths p INNER JOIN imports i ON p.id = i.to_path_id
+		WHERE i.unit_id = $1`
+	}
+	return collectStrings(ctx, db.db, query, unitID)
 }
 
 // getPackagesInUnit returns all of the packages in a unit from a
diff --git a/internal/postgres/unit_test.go b/internal/postgres/unit_test.go
index 64e0b57f..c60941b7 100644
--- a/internal/postgres/unit_test.go
+++ b/internal/postgres/unit_test.go
@@ -743,7 +743,12 @@ func TestGetUnit(t *testing.T) {
 				test.want.IsRedistributable,
 			)
 			test.want.CommitTime = um.CommitTime
-			checkUnit(ctx, t, testDB, um, test.want)
+			t.Run("none", func(t *testing.T) {
+				checkUnit(ctx, t, testDB, um, test.want)
+			})
+			t.Run(internal.ExperimentReadImports, func(t *testing.T) {
+				checkUnit(ctx, t, testDB, um, test.want, internal.ExperimentReadImports)
+			})
 		})
 	}
 }