cmd/go: report changes and resolved versions in 'go get'

Fixes #33284

Change-Id: I33daa5eb518985bc7308f29655e04c57e244b479
Reviewed-on: https://go-review.googlesource.com/c/go/+/269018
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Jay Conrod <jayconrod@google.com>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

src/cmd/go/internal/modget/get.go

@@ -45,7 +45,9 @@ import (
 	"cmd/go/internal/search"
 	"cmd/go/internal/work"
 
+	"golang.org/x/mod/modfile"
 	"golang.org/x/mod/module"
+	"golang.org/x/mod/semver"
 )
 
 var CmdGet = &base.Command{
@@ -462,10 +464,19 @@ func runGet(ctx context.Context, cmd *base.Command, args []string) {
 		// what's changing and gives more examples.
 	}
 
+	if !modload.HasModRoot() {
+		return
+	}
+
 	// Everything succeeded. Update go.mod.
+	oldReqs := reqsFromGoMod(modload.ModFile())
+
 	modload.AllowWriteGoMod()
 	modload.WriteGoMod()
 	modload.DisallowWriteGoMod()
+
+	newReqs := reqsFromGoMod(modload.ModFile())
+	r.reportChanges(oldReqs, newReqs)
 }
 
 // parseArgs parses command-line arguments and reports errors.
@@ -1563,63 +1574,69 @@ func (r *resolver) checkPackagesAndRetractions(ctx context.Context, pkgPatterns
 	}
 }
 
-// reportChanges logs resolved version changes to os.Stderr.
-func (r *resolver) reportChanges(queries []*query) {
-	for _, q := range queries {
-		if q.version == "none" {
-			continue
+// reportChanges logs version changes to os.Stderr.
+//
+// reportChanges only logs changes to modules named on the command line and to
+// explicitly required modules in go.mod. Most changes to indirect requirements
+// are not relevant to the user and are not logged.
+//
+// reportChanges should be called after WriteGoMod.
+func (r *resolver) reportChanges(oldReqs, newReqs []module.Version) {
+	type change struct {
+		path, old, new string
+	}
+	changes := make(map[string]change)
+
+	// Collect changes in modules matched by command line arguments.
+	for path, reason := range r.resolvedVersion {
+		old := r.initialVersion[path]
+		new := reason.version
+		if old != new && (old != "" || new != "none") {
+			changes[path] = change{path, old, new}
+		}
 	}
 
-		if q.pattern == "all" {
-			// To reduce noise for "all", describe module version changes rather than
-			// package versions.
-			seen := make(map[module.Version]bool)
-			for _, m := range q.resolved {
-				if seen[m] {
-					continue
+	// Collect changes to explicit requirements in go.mod.
+	for _, req := range oldReqs {
+		path := req.Path
+		old := req.Version
+		new := r.buildListVersion[path]
+		if old != new {
+			changes[path] = change{path, old, new}
+		}
+	}
+	for _, req := range newReqs {
+		path := req.Path
+		old := r.initialVersion[path]
+		new := req.Version
+		if old != new {
+			changes[path] = change{path, old, new}
 		}
-				seen[m] = true
-
-				before := r.initialSelected(m.Path)
-				if before == m.Version {
-					continue // m was resolved, but not changed
 	}
 
-				was := ""
-				if before != "" {
-					was = fmt.Sprintf(" (was %s)", before)
+	sortedChanges := make([]change, 0, len(changes))
+	for _, c := range changes {
+		sortedChanges = append(sortedChanges, c)
 	}
-				fmt.Fprintf(os.Stderr, "go: %v added %s %s%s\n", q, m.Path, m.Version, was)
-			}
-			continue
-		}
-
-		for _, m := range q.resolved {
-			before := r.initialSelected(m.Path)
-			if before == m.Version {
-				continue // m was resolved, but not changed
-			}
-
-			was := ""
-			if before != "" {
-				was = fmt.Sprintf(" (was %s)", before)
-			}
-			switch {
-			case q.isWildcard():
-				if q.matchesPath(m.Path) {
-					fmt.Fprintf(os.Stderr, "go: matched %v as %s %s%s\n", q, m.Path, m.Version, was)
+	sort.Slice(sortedChanges, func(i, j int) bool {
+		return sortedChanges[i].path < sortedChanges[j].path
+	})
+	for _, c := range sortedChanges {
+		if c.old == "" {
+			fmt.Fprintf(os.Stderr, "go get: added %s %s\n", c.path, c.new)
+		} else if c.new == "none" || c.new == "" {
+			fmt.Fprintf(os.Stderr, "go get: removed %s %s\n", c.path, c.old)
+		} else if semver.Compare(c.new, c.old) > 0 {
+			fmt.Fprintf(os.Stderr, "go get: upgraded %s %s => %s\n", c.path, c.old, c.new)
 		} else {
-					fmt.Fprintf(os.Stderr, "go: matched %v in %s %s%s\n", q, m.Path, m.Version, was)
-				}
-			case q.matchesPackages:
-				fmt.Fprintf(os.Stderr, "go: found %v in %s %s%s\n", q, m.Path, m.Version, was)
-			default:
-				fmt.Fprintf(os.Stderr, "go: found %v in %s %s%s\n", q, m.Path, m.Version, was)
-			}
+			fmt.Fprintf(os.Stderr, "go get: downgraded %s %s => %s\n", c.path, c.old, c.new)
 		}
 	}
 
-	// TODO(#33284): Also print relevant upgrades.
+	// TODO(golang.org/issue/33284): attribute changes to command line arguments.
+	// For modules matched by command line arguments, this probably isn't
+	// necessary, but it would be useful for unmatched direct dependencies of
+	// the main module.
 }
 
 // resolve records that module m must be at its indicated version (which may be
@@ -1700,6 +1717,14 @@ func (r *resolver) updateBuildList(ctx context.Context, additions []module.Versi
 	return true
 }
 
+func reqsFromGoMod(f *modfile.File) []module.Version {
+	reqs := make([]module.Version, len(f.Require))
+	for i, r := range f.Require {
+		reqs[i] = r.Mod
+	}
+	return reqs
+}
+
 // isNoSuchModuleVersion reports whether err indicates that the requested module
 // does not exist at the requested version, either because the module does not
 // exist at all or because it does not include that specific version.

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

@@ -0,0 +1,70 @@
+# When adding a requirement, 'go get' prints a message for the requirement
+# and for changed explicit dependencies. 'go get' does not print messages
+# for changed indirect dependencies.
+go list -m all
+! stdout golang.org/x/text
+go get -d rsc.io/quote@v1.5.2
+stderr '^go get: added rsc.io/quote v1.5.2$'
+stderr '^go get: upgraded rsc.io/sampler v1.0.0 => v1.3.0$'
+! stderr '^go get.*golang.org/x/text'
+go list -m all
+stdout golang.org/x/text
+cmp go.mod go.mod.upgrade
+
+# When removing a requirement, 'go get' prints a message for the requiremnent
+# and for changed explicit dependencies. 'go get' does not print messages
+# for changed indirect dependencies.
+go get -d rsc.io/sampler@none
+stderr '^go get: downgraded rsc.io/quote v1.5.2 => v1.3.0$'
+stderr '^go get: removed rsc.io/sampler v1.3.0$'
+! stderr '^go get.*golang.org/x/text'
+cmp go.mod go.mod.downgrade
+
+# When removing or downgrading a requirement, 'go get' also prints a message
+# for explicit dependencies removed as a consequence.
+cp go.mod.usequote go.mod
+go get -d rsc.io/quote@v1.5.1
+stderr '^go get: downgraded rsc.io/quote v1.5.2 => v1.5.1$'
+stderr '^go get: removed usequote v0.0.0$'
+
+-- go.mod --
+module m
+
+go 1.16
+
+require rsc.io/sampler v1.0.0
+-- go.sum --
+rsc.io/sampler v1.0.0 h1:SRJnjyQ07sAtq6G4RcfJEmz8JxqLyj3PoGXG2VhbDWo=
+rsc.io/sampler v1.0.0/go.mod h1:cqxpM3ZVz9VtirqxZPmrWzkQ+UkiNiGtkrN+B+i8kx8=
+-- go.mod.upgrade --
+module m
+
+go 1.16
+
+require (
+	rsc.io/quote v1.5.2 // indirect
+	rsc.io/sampler v1.3.0
+)
+-- go.mod.downgrade --
+module m
+
+go 1.16
+
+require (
+	golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c // indirect
+	rsc.io/quote v1.3.0 // indirect
+)
+-- go.mod.usequote --
+module m
+
+go 1.16
+
+require usequote v0.0.0
+
+replace usequote => ./usequote
+-- usequote/go.mod --
+module usequote
+
+go 1.16
+
+require rsc.io/quote v1.5.2