cmd/go: do not allow version prefixes to match prereleases of that version

Fixes #31972

Change-Id: I3bb9ef3a1134e67d2d062bea2f0e4032647e12e6
Reviewed-on: https://go-review.googlesource.com/c/go/+/176898
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

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

@@ -186,7 +186,7 @@ func Query(path, query string, allowed func(module.Version) bool) (*modfetch.Rev
 	return nil, &NoMatchingVersionError{query: query}
 }
 
-// isSemverPrefix reports whether v is a semantic version prefix: v1 or  v1.2 (not wv1.2.3).
+// isSemverPrefix reports whether v is a semantic version prefix: v1 or v1.2 (not v1.2.3).
 // The caller is assumed to have checked that semver.IsValid(v) is true.
 func isSemverPrefix(v string) bool {
 	dots := 0
@@ -207,7 +207,7 @@ func isSemverPrefix(v string) bool {
 // matchSemverPrefix reports whether the shortened semantic version p
 // matches the full-width (non-shortened) semantic version v.
 func matchSemverPrefix(p, v string) bool {
-	return len(v) > len(p) && v[len(p)] == '.' && v[:len(p)] == p
+	return len(v) > len(p) && v[len(p)] == '.' && v[:len(p)] == p && semver.Prerelease(v) == ""
 }
 
 type QueryResult struct {

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

@@ -76,7 +76,7 @@ var queryTests = []struct {
 		git checkout v2
 		echo module vcs-test.golang.org/git/querytest.git/v2 >go.mod
 		git commit -m v2 go.mod
-		for i in v2.0.0 v2.1.0 v2.2.0 v2.5.5; do
+		for i in v2.0.0 v2.1.0 v2.2.0 v2.5.5 v2.6.0-pre1; do
 			echo before $i >status
 			git add status
 			git commit -m "before $i" status
@@ -84,6 +84,7 @@ var queryTests = []struct {
 			git commit -m "at $i" status
 			git tag $i
 		done
+		git checkout v2.5.5
 		echo after v2.5.5 >status
 		git commit -m 'after v2.5.5' status
 		git checkout master
@@ -117,6 +118,10 @@ var queryTests = []struct {
 	{path: queryRepoV2, query: ">v0.0.0", vers: "v2.0.0"},
 	{path: queryRepoV2, query: ">=v0.0.0", vers: "v2.0.0"},
 	{path: queryRepoV2, query: "v0.0.1+foo", vers: "v2.0.0-20180704023347-179bc86b1be3"},
+	{path: queryRepoV2, query: "v2", vers: "v2.5.5"},
+	{path: queryRepoV2, query: "v2.5", vers: "v2.5.5"},
+	{path: queryRepoV2, query: "v2.6", err: `no matching versions for query "v2.6"`},
+	{path: queryRepoV2, query: "v2.6.0-pre1", vers: "v2.6.0-pre1"},
 	{path: queryRepoV2, query: "latest", vers: "v2.5.5"},
 
 	{path: queryRepoV3, query: "latest", vers: "v3.0.0-20180704024501-e0cf3de987e6"},

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

@@ -3,13 +3,21 @@ env GO111MODULE=on
 go list -m -versions rsc.io/quote
 stdout '^rsc.io/quote v1.0.0 v1.1.0 v1.2.0 v1.2.1 v1.3.0 v1.4.0 v1.5.0 v1.5.1 v1.5.2 v1.5.3-pre1$'
 
-# latest rsc.io/quote should be v1.5.2 not v1.5.3-pre1
+# Latest rsc.io/quote should be v1.5.2, not v1.5.3-pre1.
 go list -m rsc.io/quote@latest
 stdout 'rsc.io/quote v1.5.2$'
 
+# Same for rsc.io/quote@v1 and rsc.io/quote@v1.5 (with no patch version).
+go list -m rsc.io/quote@v1
+stdout 'rsc.io/quote v1.5.2$'
+go list -m rsc.io/quote@v1.5
+stdout 'rsc.io/quote v1.5.2$'
+
+# We should fall back to prereleases if no release tags match...
 go list -m rsc.io/quote@>v1.5.2
 stdout 'rsc.io/quote v1.5.3-pre1$'
 
+# ...but prefer release versions when given the option.
 go list -m rsc.io/quote@<v1.5.4
 stdout 'rsc.io/quote v1.5.2$'