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, 20 insertions, 0 deletions

diff --git a/internal/fetchdatasource/fetchdatasource.go b/internal/fetchdatasource/fetchdatasource.go
index 1643d009..7a5f5669 100644
--- a/internal/fetchdatasource/fetchdatasource.go
+++ b/internal/fetchdatasource/fetchdatasource.go
@@ -433,3 +433,23 @@ func (ds *FetchDataSource) GetModulePackages(ctx context.Context, modulePath, ve
 	}
 	return metas, nil
 }
+
+// GetSymbols returns symbols for the given unit and build context.
+func (ds *FetchDataSource) GetSymbols(ctx context.Context, pkgPath, modulePath, version string, bc internal.BuildContext) (_ []*internal.Symbol, err error) {
+	defer derrors.Wrap(&err, "FetchDataSource.GetSymbols(%q, %q, %q, %v)", pkgPath, modulePath, version, bc)
+
+	m, err := ds.getModule(ctx, modulePath, version)
+	if err != nil {
+		return nil, err
+	}
+	unit, err := ds.findUnit(ctx, m, pkgPath)
+	if err != nil {
+		return nil, err
+	}
+
+	doc := matchingDoc(unit.Documentation, bc)
+	if doc == nil || len(doc.API) == 0 {
+		return nil, derrors.NotFound
+	}
+	return doc.API, nil
+}