…ract directives

VersionFixers require both a path and a version: if the version is
non-canonical (like a branch name), they generally need the path to
look up the proper version. This is fine for require, replace, and
exclude directives, since the path is specified with each version. For
retract directives, the path comes from the module directive, which
may appear later in the file. Previously, we just used the empty
string, but this breaks reasonable implementations.

With this change, we leave retracted versions alone until the file has
been completely parsed, then we apply the version fixer to each
retract directive. We report an error if retract is used without a
module directive.

For golang/go#44496

Change-Id: I99b7b8b55941c1fde4ee56161acfe854bcaf948d
Reviewed-on: https://go-review.googlesource.com/c/mod/+/296130
Trust: Jay Conrod <jayconrod@google.com>
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
(cherry picked from commit 66bf157)
Reviewed-on: https://go-review.googlesource.com/c/mod/+/298010
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

…arser

modfile.Parse passed an empty string to the VersionFixer for the
module path. This caused errors for v2+ versions.

For #44496

Change-Id: I13b86b6ecf6815c4bc9a96ec0668284c9228c205
Reviewed-on: https://go-review.googlesource.com/c/go/+/296131
Trust: Jay Conrod <jayconrod@google.com>
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
(cherry picked from commit bcac57f)
Reviewed-on: https://go-review.googlesource.com/c/go/+/297990
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

…ing canonical versions

If a canonical version is passed to fixVersion when loading the main
go.mod and that version don't match the module path's major version
suffix, don't call Query.

Query doesn't return a useful error in this case when the path is
malformed, for example, when it doens't have a dot in the first path
element. It's better to report the major version mismatch error.

Fixes #44496

Change-Id: I97b1f64aee894fa0db6fb637aa03a51357ee782c
Reviewed-on: https://go-review.googlesource.com/c/go/+/296590
Trust: Jay Conrod <jayconrod@google.com>
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
(cherry picked from commit 5fafc0b)
Reviewed-on: https://go-review.googlesource.com/c/go/+/297989
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>