internal/lsp: label context cancellation errors

This change will just make it a bit easier to debug the context
cancellation errors.

Change-Id: I580751ac04e3357031678eb31914828029c96e4b
Reviewed-on: https://go-review.googlesource.com/c/tools/+/190412
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Cottrell <iancottrell@google.com>

internal/lsp/cache/check.go

@@ -128,7 +128,7 @@ func (cph *checkPackageHandle) Check(ctx context.Context) (source.Package, error
 func (cph *checkPackageHandle) check(ctx context.Context) (*pkg, error) {
 	v := cph.handle.Get(ctx)
 	if v == nil {
-		return nil, ctx.Err()
+		return nil, errors.Errorf("check: %v", ctx.Err())
 	}
 	data := v.(*checkPackageData)
 	return data.pkg, data.err

internal/lsp/cache/load.go

@@ -80,7 +80,7 @@ func (v *view) checkMetadata(ctx context.Context, f *goFile) (map[packageID]*met
 
 	// Check if the context has been canceled before calling packages.Load.
 	if ctx.Err() != nil {
-		return nil, ctx.Err()
+		return nil, errors.Errorf("checkMetadata: %v", ctx.Err())
 	}
 
 	ctx, done := trace.StartSpan(ctx, "packages.Load", telemetry.File.Of(f.filename()))

internal/lsp/cache/parse.go

@@ -70,7 +70,7 @@ func (h *parseGoHandle) Mode() source.ParseMode {
 func (h *parseGoHandle) Parse(ctx context.Context) (*ast.File, error) {
 	v := h.handle.Get(ctx)
 	if v == nil {
-		return nil, ctx.Err()
+		return nil, errors.Errorf("Parse: %v", ctx.Err())
 	}
 	data := v.(*parseGoData)
 	return data.ast, data.err

internal/lsp/cache/pkg.go

@@ -14,6 +14,7 @@ import (
 	"golang.org/x/tools/go/analysis"
 	"golang.org/x/tools/go/packages"
 	"golang.org/x/tools/internal/lsp/source"
+	errors "golang.org/x/xerrors"
 )
 
 // pkg contains the type information needed by the source package.
@@ -55,10 +56,6 @@ type analysisEntry struct {
 }
 
 func (pkg *pkg) GetActionGraph(ctx context.Context, a *analysis.Analyzer) (*source.Action, error) {
-	if ctx.Err() != nil {
-		return nil, ctx.Err()
-	}
-
 	pkg.mu.Lock()
 	e, ok := pkg.analyses[a]
 	if ok {
@@ -75,7 +72,7 @@ func (pkg *pkg) GetActionGraph(ctx context.Context, a *analysis.Analyzer) (*sour
 				return pkg.GetActionGraph(ctx, a)
 			}
 		case <-ctx.Done():
-			return nil, ctx.Err()
+			return nil, errors.Errorf("GetActionGraph: %v", ctx.Err())
 		}
 	} else {
 		// cache miss

internal/lsp/cache/token.go

@@ -51,7 +51,7 @@ func (h *tokenHandle) File() source.FileHandle {
 func (h *tokenHandle) Token(ctx context.Context) (*token.File, error) {
 	v := h.handle.Get(ctx)
 	if v == nil {
-		return nil, ctx.Err()
+		return nil, errors.Errorf("Token: %v", ctx.Err())
 	}
 	data := v.(*tokenData)
 	return data.tok, data.err

internal/lsp/source/analysis.go

@@ -26,8 +26,9 @@ import (
 func analyze(ctx context.Context, v View, cphs []CheckPackageHandle, analyzers []*analysis.Analyzer) ([]*Action, error) {
 	ctx, done := trace.StartSpan(ctx, "source.analyze")
 	defer done()
+
 	if ctx.Err() != nil {
-		return nil, ctx.Err()
+		return nil, errors.Errorf("analyze: %v", ctx.Err())
 	}
 
 	// Build nodes for initial packages.