cmd/go/internal/get: complete implementation

The original prototype only supported "go get thing"
and "go get -u" but not the obvious "go get -u thing".
Fix that.

Also add "go get -u=patch", as promised in the proposal.
(There it was called "-p", but that's a build flag already.)

Redefine "go get -m" (not implemented until now) to mean
"only update go.mod".

Fixes golang/go#24105.
Fixes golang/go#24486.

Change-Id: I981a86cf2b283f8d05e404292fa5d3482540105c
Reviewed-on: https://go-review.googlesource.com/122396
Reviewed-by: Bryan C. Mills <bcmills@google.com>

vendor/cmd/go/internal/modfetch/coderepo.go

@@ -140,7 +140,6 @@ func (r *codeRepo) Latest() (*RevInfo, error) {
 }
 
 func (r *codeRepo) convert(info *codehost.RevInfo, statVers string) (*RevInfo, error) {
-
 	info2 := &RevInfo{
 		Name:  info.Name,
 		Short: info.Short,
@@ -184,6 +183,17 @@ func (r *codeRepo) convert(info *codehost.RevInfo, statVers string) (*RevInfo, e
 		}
 	}
 
+	// Do not allow a successful stat of a pseudo-version for a subdirectory
+	// unless the subdirectory actually does have a go.mod.
+	if IsPseudoVersion(info2.Version) && r.codeDir != "" {
+		_, _, _, err := r.findDir(info2.Version)
+		if err != nil {
+			// TODO: It would be nice to return an error like "not a module".
+			// Right now we return "missing go.mod", which is a little confusing.
+			return nil, err
+		}
+	}
+
 	return info2, nil
 }
 

vendor/cmd/go/internal/modfetch/coderepo_test.go

@@ -259,13 +259,10 @@ var codeRepoTests = []struct {
 	},
 	{
 		// package in subdirectory - github
-		path:     "github.com/rsc/quote/buggy",
-		rev:      "c4d4236f",
-		version:  "v0.0.0-20180214154420-c4d4236f9242",
-		name:     "c4d4236f92427c64bfbcf1cc3f8142ab18f30b22",
-		short:    "c4d4236f9242",
-		time:     time.Date(2018, 2, 14, 15, 44, 20, 0, time.UTC),
-		gomoderr: "missing go.mod",
+		// Because it's a package, Stat should fail entirely.
+		path: "github.com/rsc/quote/buggy",
+		rev:  "c4d4236f",
+		err:  "missing go.mod",
 	},
 	{
 		path:    "gopkg.in/yaml.v2",
@@ -599,6 +596,10 @@ var latestTests = []struct {
 		path:    "github.com/rsc/vgotest1",
 		version: "v0.0.0-20180219223237-a08abb797a67",
 	},
+	{
+		path: "github.com/rsc/vgotest1/subdir",
+		err:  "missing go.mod",
+	},
 	{
 		path:    "swtch.com/testmod",
 		version: "v1.1.1",
@@ -630,6 +631,9 @@ func TestLatest(t *testing.T) {
 				}
 				t.Fatalf("Latest(): %v", err)
 			}
+			if tt.err != "" {
+				t.Fatalf("Latest() = %v, want error %q", info.Version, tt.err)
+			}
 			if info.Version != tt.version {
 				t.Fatalf("Latest() = %v, want %v", info.Version, tt.version)
 			}

vendor/cmd/go/internal/modfetch/repo.go

@@ -269,6 +269,8 @@ func Import(path string, allowed func(module.Version) bool) (Repo, *RevInfo, err
 		// source code and check that it actually contains code for the
 		// target import path. To do that efficiently we will need to move
 		// the unzipped code cache out of ../modload into this package.
+		// TODO(rsc): When this happens, look carefully at the use of
+		// modfetch.Import in modget.getQuery.
 		return r, info, nil
 	}