cmd/go: make 'go mod why -m' work in inconsistent, pruned module

'go mod why -m' works by listing modules matching command line
arguments, then loading "all" packages and finding which of the listed
modules provide packages imported by the main module.

If go.mod is inconsistent (that is, a requirement has a lower version
than MVS would select when the module graph is loaded) and pruned
(that is, the module graph is only loaded when necessary), then
modload.ListModules may return modules with different versions than
would be selected in modload.LoadPackages.

'go mod why -m' was too strict about this, mapping module paths and
versions to packages. With this fix, it maps module paths without
versions to packages.

Fixes #48613

Change-Id: I836c46289bb647d6c46ec65e7589531da532d5e8
Reviewed-on: https://go-review.googlesource.com/c/go/+/352115
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>

diff --git a/src/cmd/go/internal/modcmd/why.go b/src/cmd/go/internal/modcmd/why.go
index 9647784b67a4acb8a88d6210cf2158c13eae74f2..d8355cca957a460788b1f7f146679c79bdfe169c 100644 (file)
--- a/src/cmd/go/internal/modcmd/why.go
+++ b/src/cmd/go/internal/modcmd/why.go
@@ -12,8 +12,6 @@ import (
        "cmd/go/internal/base"
        "cmd/go/internal/imports"
        "cmd/go/internal/modload"
-
-       "golang.org/x/mod/module"
 )
 
 var cmdWhy = &base.Command{
@@ -90,19 +88,19 @@ func runWhy(ctx context.Context, cmd *base.Command, args []string) {
                        base.Fatalf("go: %v", err)
                }
 
-               byModule := make(map[module.Version][]string)
+               byModule := make(map[string][]string)
                _, pkgs := modload.LoadPackages(ctx, loadOpts, "all")
                for _, path := range pkgs {
                        m := modload.PackageModule(path)
                        if m.Path != "" {
-                               byModule[m] = append(byModule[m], path)
+                               byModule[m.Path] = append(byModule[m.Path], path)
                        }
                }
                sep := ""
                for _, m := range mods {
                        best := ""
                        bestDepth := 1000000000
-                       for _, path := range byModule[module.Version{Path: m.Path, Version: m.Version}] {
+                       for _, path := range byModule[m.Path] {
                                d := modload.WhyDepth(path)
                                if d > 0 && d < bestDepth {
                                        best = path

diff --git a/src/cmd/go/testdata/script/mod_skip_write.txt b/src/cmd/go/testdata/script/mod_skip_write.txt
index c3e5906589f46f59ac1e0055def2200f2be1120c..9fdb6fc121258721def75cb83756988a7621d388 100644 (file)
--- a/src/cmd/go/testdata/script/mod_skip_write.txt
+++ b/src/cmd/go/testdata/script/mod_skip_write.txt
@@ -24,9 +24,8 @@ go mod why rsc.io/sampler
 cmp stdout why.want
 cmp go.mod go.mod.edit
 
-# TODO(#48613): 'go mod why -m' incorrectly reports sampler is not needed.
 go mod why -m rsc.io/sampler
-cmp stdout why-broken.want
+cmp stdout why.want
 cmp go.mod go.mod.edit
 
 cp go.mod.orig go.mod
@@ -91,6 +90,3 @@ rsc.io/sampler@v1.3.0 golang.org/x/text@v0.0.0-20170915032832-14c0d48ead0c
 m
 rsc.io/quote
 rsc.io/sampler
--- why-broken.want --
-# rsc.io/sampler
-(main module does not need module rsc.io/sampler)