cmd/go: clarify error when package is removed in a module

If no module in the build list provides an imported package, we
try to upgrade to the "@latest" version. If there is a requirement on
a version of the module which is newer than the "@latest" version
(e.g., a prerelease or pseudoversion), we cannot upgrade further.

We previously reported "looping trying to add package" when we saw the
package in "@latest" but it was removed later. The meaning of this is
unclear for users, so with this change, we explain the package was
removed.

Fixes #30394

Change-Id: I1b7fec2c37e762fb600e66ee8a4df4aeaf13e67a
Reviewed-on: https://go-review.googlesource.com/c/go/+/169720
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/src/cmd/go/internal/modload/load.go b/src/cmd/go/internal/modload/load.go
index 71b7308c0d..57c2dd25a6 100644
--- a/src/cmd/go/internal/modload/load.go
+++ b/src/cmd/go/internal/modload/load.go
@@ -547,6 +547,9 @@ func (ld *loader) load(roots func() []string) {
 		}
 		for _, pkg := range ld.pkgs {
 			if err, ok := pkg.err.(*ImportMissingError); ok && err.Module.Path != "" {
+				if err.newMissingVersion != "" {
+					base.Fatalf("go: %s: package provided by %s at latest version %s but not at required version %s", pkg.stackText(), err.Module.Path, err.Module.Version, err.newMissingVersion)
+				}
 				if added[pkg.path] {
 					base.Fatalf("go: %s: looping trying to add package", pkg.stackText())
 				}