internal: consolidate build context and unit resolution logic

- Centralize logic for resolving units and selecting the best matching
  build context.
- New helpers MatchingBuildContext, SortedBuildContexts provide a
  consistent, efficient approach to build context selection.
- DocumentationForBuildContext now finds the best match based on
  precdence rules rather than just returning the first match.
- A new getUnitContext helper resolves unit metadata and the best build
  context in a single query.
- GetSymbols and GetUnit are now both optimized to use pre-resolved IDs,
  simplifying their queries and removing redundant joins.
- Replaced redundant matchingDoc functions in fetchdatasource and
  fakedatasource.

Change-Id: I9207d3bfe03404483c816090a0b99666f14a36e3
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/759162
Reviewed-by: Jonathan Amsterdam <jba@google.com>
kokoro-CI: kokoro <noreply+kokoro@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Ethan Lee <ethanalee@google.com>

1 files changed, 2 insertions, 19 deletions

diff --git a/internal/fetchdatasource/fetchdatasource.go b/internal/fetchdatasource/fetchdatasource.go
index 7a5f5669..dfe30fc9 100644
--- a/internal/fetchdatasource/fetchdatasource.go
+++ b/internal/fetchdatasource/fetchdatasource.go
@@ -220,7 +220,7 @@ func (ds *FetchDataSource) GetUnit(ctx context.Context, um *internal.UnitMeta, f
 	// Since we cache the module and its units, we have to copy this unit before we modify it.
 	// It can be a shallow copy, since we're only modifying the Unit.Documentation field.
 	u2 := *u
-	if d := matchingDoc(u.Documentation, bc); d != nil {
+	if d := internal.DocumentationForBuildContext(u.Documentation, bc); d != nil {
 		u2.Documentation = []*internal.Documentation{d}
 	} else {
 		u2.Documentation = nil
@@ -252,23 +252,6 @@ func findUnitMeta(m *fetch.LazyModule, path string) (*internal.UnitMeta, error)
 	return nil, derrors.NotFound
 }
 
-// matchingDoc returns the Documentation that matches the given build context
-// and comes earliest in build-context order. It returns nil if there is none.
-func matchingDoc(docs []*internal.Documentation, bc internal.BuildContext) *internal.Documentation {
-	var (
-		dMin  *internal.Documentation
-		bcMin = internal.BuildContext{GOOS: "unk", GOARCH: "unk"} // sorts last
-	)
-	for _, d := range docs {
-		dbc := d.BuildContext()
-		if bc.Match(dbc) && internal.CompareBuildContexts(dbc, bcMin) < 0 {
-			dMin = d
-			bcMin = dbc
-		}
-	}
-	return dMin
-}
-
 // GetLatestInfo returns latest information for unitPath and modulePath.
 func (ds *FetchDataSource) GetLatestInfo(ctx context.Context, unitPath, modulePath string, latestUnitMeta *internal.UnitMeta) (latest internal.LatestInfo, err error) {
 	defer derrors.Wrap(&err, "FetchDataSource.GetLatestInfo(ctx, %q, %q)", unitPath, modulePath)
@@ -447,7 +430,7 @@ func (ds *FetchDataSource) GetSymbols(ctx context.Context, pkgPath, modulePath,
 		return nil, err
 	}
 
-	doc := matchingDoc(unit.Documentation, bc)
+	doc := internal.DocumentationForBuildContext(unit.Documentation, bc)
 	if doc == nil || len(doc.API) == 0 {
 		return nil, derrors.NotFound
 	}