internal/api: implement package symbols endpoint

- Introduce a new ServePackageSymbols handler that utilizes the new
  db.GetSymbols method.
- Consolidated module resolution logic shared by ServePackages into
  resolveModulePath.
- Updated Datasource with GetSymbols, which provides a more efficient
  way to retrieve all symbols for a package at a given version and build
  context. This differs from the existing getPackageSymbols, since that
  will return symbols for the latest release/compatible version.
- Refactored packageSymbolQueryJoin into a generic helper by removing
  hardcoded version filters. This allows GetSymbols to query for any
  specific version, while getPackageSymbols was updated to explicitly
  include release-only filters to preserve its existing behavior.
- GetSymbols still utilizes the same underlying packageSymbolQueryJoin,
  but it will also attempt to match the most relevant BuildContext for
  the query. It will also provide a mapping of parent and child symbols.

Change-Id: Ib18d2511d24ac6bc5b75c7b3809c4ce126245036
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/754864
Auto-Submit: Ethan Lee <ethanalee@google.com>
kokoro-CI: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jonathan Amsterdam <jba@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

1 files changed, 28 insertions, 0 deletions

diff --git a/internal/testing/fakedatasource/fakedatasource.go b/internal/testing/fakedatasource/fakedatasource.go
index 82212163..b44212a0 100644
--- a/internal/testing/fakedatasource/fakedatasource.go
+++ b/internal/testing/fakedatasource/fakedatasource.go
@@ -337,6 +337,34 @@ func (ds *FakeDataSource) GetModulePackages(ctx context.Context, modulePath, ver
 	return pkgs, nil
 }
 
+// GetSymbols returns symbols for the given unit and build context.
+func (ds *FakeDataSource) GetSymbols(ctx context.Context, pkgPath, modulePath, version string, bc internal.BuildContext) ([]*internal.Symbol, error) {
+	m := ds.getModule(modulePath, version)
+	if m == nil {
+		return nil, derrors.NotFound
+	}
+	u := findUnit(m, pkgPath)
+	if u == nil {
+		return nil, derrors.NotFound
+	}
+
+	var bcs []internal.BuildContext
+	for b := range u.Symbols {
+		if bc.Match(b) {
+			bcs = append(bcs, b)
+		}
+	}
+	if len(bcs) == 0 {
+		return nil, derrors.NotFound
+	}
+
+	sort.Slice(bcs, func(i, j int) bool {
+		return internal.CompareBuildContexts(bcs[i], bcs[j]) < 0
+	})
+
+	return u.Symbols[bcs[0]], nil
+}
+
 // SearchSupport reports the search types supported by this datasource.
 func (ds *FakeDataSource) SearchSupport() internal.SearchSupport {
 	// internal/frontend.TestDetermineSearchAction depends on us returning FullSearch