cmd/go: do context propagation for tracing downloads

This change does context propagation (and only context propagation)
necessary to add context to modfetch.Download and pkg.LoadImport.
This was done by adding context to their callers, and then
adding context to all call-sites, and then repeating adding
context to callers of those enclosing functions and their
callers until none were left. In some cases the call graph expansion
was pruned by using context.TODOs.

The next CL will add a span to Download. I kept it out of this
change to avoid making it any larger (and harder to review)
than it needs to be.

Updates #38714

Change-Id: I7a03416e04a14ca71636d96f2c1bda2c4c30d348
Reviewed-on: https://go-review.googlesource.com/c/go/+/249021
Run-TryBot: Michael Matloob <matloob@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

1 files changed, 5 insertions, 4 deletions

diff --git a/src/cmd/go/internal/modload/import.go b/src/cmd/go/internal/modload/import.go
index 4d2bc805e2..5c51a79124 100644
--- a/src/cmd/go/internal/modload/import.go
+++ b/src/cmd/go/internal/modload/import.go
@@ -5,6 +5,7 @@
 package modload
 
 import (
+	"context"
 	"errors"
 	"fmt"
 	"go/build"
@@ -110,7 +111,7 @@ var _ load.ImportPathError = &AmbiguousImportError{}
 // Import returns an ImportMissingError as the error.
 // If Import can identify a module that could be added to supply the package,
 // the ImportMissingError records that module.
-func Import(path string) (m module.Version, dir string, err error) {
+func Import(ctx context.Context, path string) (m module.Version, dir string, err error) {
 	if strings.Contains(path, "@") {
 		return module.Version{}, "", fmt.Errorf("import path should not have @version")
 	}
@@ -165,7 +166,7 @@ func Import(path string) (m module.Version, dir string, err error) {
 			// Avoid possibly downloading irrelevant modules.
 			continue
 		}
-		root, isLocal, err := fetch(m)
+		root, isLocal, err := fetch(ctx, m)
 		if err != nil {
 			// Report fetch error.
 			// Note that we don't know for sure this module is necessary,
@@ -248,7 +249,7 @@ func Import(path string) (m module.Version, dir string, err error) {
 			return len(mods[i].Path) > len(mods[j].Path)
 		})
 		for _, m := range mods {
-			root, isLocal, err := fetch(m)
+			root, isLocal, err := fetch(ctx, m)
 			if err != nil {
 				// Report fetch error as above.
 				return module.Version{}, "", err
@@ -285,7 +286,7 @@ func Import(path string) (m module.Version, dir string, err error) {
 
 	fmt.Fprintf(os.Stderr, "go: finding module for package %s\n", path)
 
-	candidates, err := QueryPackage(path, "latest", Allowed)
+	candidates, err := QueryPackage(ctx, path, "latest", Allowed)
 	if err != nil {
 		if errors.Is(err, os.ErrNotExist) {
 			// Return "cannot find module providing package […]" instead of whatever