cmd/go: reject 'go list -m MOD@patch' when no existing version of MOD is required

Noticed while debugging failing tests for #36460.

Fixes #44788

Change-Id: Ic2cf511d871b29284f7372920f6f7d452825dd63
Reviewed-on: https://go-review.googlesource.com/c/go/+/298651
Trust: Bryan C. Mills <[email protected]>
Run-TryBot: Bryan C. Mills <[email protected]>
Reviewed-by: Jay Conrod <[email protected]>
TryBot-Result: Go Bot <[email protected]>

Author: Bryan C. Mills

src/cmd/go/internal/modload/list.go

@@ -78,7 +78,7 @@ func listModules(ctx context.Context, args []string, listVersions, listRetracted
 		if i := strings.Index(arg, "@"); i >= 0 {
 			path := arg[:i]
 			vers := arg[i+1:]
-			var current string
+			current := "none"
 			for _, m := range buildList {
 				if m.Path == path {
 					current = m.Version

src/cmd/go/internal/modload/query.go

@@ -330,7 +330,7 @@ func newQueryMatcher(path string, query, current string, allowed AllowedFunc) (*
 		}
 
 	case query == "patch":
-		if current == "none" {
+		if current == "" || current == "none" {
 			return nil, &NoPatchBaseError{path}
 		}
 		if current == "" {

src/cmd/go/internal/modload/query_test.go

@@ -122,7 +122,7 @@ var queryTests = []struct {
 	{path: queryRepo, query: "upgrade", allow: "NOMATCH", err: `no matching versions for query "upgrade"`},
 	{path: queryRepo, query: "upgrade", current: "v1.9.9", allow: "NOMATCH", err: `vcs-test.golang.org/git/[email protected]: disallowed module version`},
 	{path: queryRepo, query: "upgrade", current: "v1.99.99", err: `vcs-test.golang.org/git/[email protected]: invalid version: unknown revision v1.99.99`},
-	{path: queryRepo, query: "patch", current: "", vers: "v1.9.9"},
+	{path: queryRepo, query: "patch", current: "", err: `can't query version "patch" of module vcs-test.golang.org/git/querytest.git: no existing version is required`},
 	{path: queryRepo, query: "patch", current: "v0.1.0", vers: "v0.1.2"},
 	{path: queryRepo, query: "patch", current: "v1.9.0", vers: "v1.9.9"},
 	{path: queryRepo, query: "patch", current: "v1.9.10-pre1", vers: "v1.9.10-pre1"},

src/cmd/go/testdata/script/mod_prefer_compatible.txt

@@ -23,8 +23,8 @@ stdout '^github.com/russross/blackfriday v1\.'
 go list -m github.com/russross/blackfriday@upgrade
 stdout '^github.com/russross/blackfriday v1\.'
 
-go list -m github.com/russross/blackfriday@patch
-stdout '^github.com/russross/blackfriday v1\.'
+! go list -m github.com/russross/blackfriday@patch
+stderr '^go list -m: github.com/russross/blackfriday@patch: can''t query version "patch" of module github.com/russross/blackfriday: no existing version is required$'
 
 # If we're fetching directly from version control, ignored +incompatible
 # versions should also be omitted by 'go list'.