cmd/go: fix go get go@badversion

It was panicking instead of printing a nice error.

Fixes golang#61258.
Fixes golang#61259.

Change-Id: Ia30853db5bc7f1f2a4c7e91169c659ae2b79adcb
Reviewed-on: https://go-review.googlesource.com/c/go/+/509097
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>

src/cmd/go/internal/modfetch/toolchain.go

@@ -60,6 +60,15 @@ func (r *toolchainRepo) Versions(ctx context.Context, prefix string) (*Versions,
 		}
 	}
 
+	// Always include our own version.
+	// This means that the development branch of Go 1.21 (say) will allow 'go get go@1.21'
+	// even though there are no Go 1.21 releases yet.
+	// Once there is a release, 1.21 will be treated as a query matching the latest available release.
+	// Before then, 1.21 will be treated as a query that resolves to this entry we are adding (1.21).
+	if v := gover.Local(); !have[v] {
+		list = append(list, goPrefix+v)
+	}
+
 	if r.path == "go" {
 		sort.Slice(list, func(i, j int) bool {
 			return gover.Compare(list[i], list[j]) < 0
@@ -74,20 +83,27 @@ func (r *toolchainRepo) Versions(ctx context.Context, prefix string) (*Versions,
 }
 
 func (r *toolchainRepo) Stat(ctx context.Context, rev string) (*RevInfo, error) {
-	// If we're asking about "go" (not "toolchain"), pretend to have
-	// all earlier Go versions available without network access:
-	// we will provide those ourselves, at least in GOTOOLCHAIN=auto mode.
-	if r.path == "go" && gover.Compare(rev, gover.Local()) <= 0 {
-		return &RevInfo{Version: rev}, nil
-	}
-
 	// Convert rev to DL version and stat that to make sure it exists.
+	// In theory the go@ versions should be like 1.21.0
+	// and the toolchain@ versions should be like go1.21.0
+	// but people will type the wrong one, and so we accept
+	// both and silently correct it to the standard form.
 	prefix := ""
 	v := rev
 	v = strings.TrimPrefix(v, "go")
 	if r.path == "toolchain" {
 		prefix = "go"
 	}
+
+	if !gover.IsValid(v) {
+		return nil, fmt.Errorf("invalid %s version %s", r.path, rev)
+	}
+	// If we're asking about "go" (not "toolchain"), pretend to have
+	// all earlier Go versions available without network access:
+	// we will provide those ourselves, at least in GOTOOLCHAIN=auto mode.
+	if r.path == "go" && gover.Compare(v, gover.Local()) <= 0 {
+		return &RevInfo{Version: prefix + v}, nil
+	}
 	if gover.IsLang(v) {
 		return nil, fmt.Errorf("go language version %s is not a toolchain version", rev)
 	}

src/cmd/go/internal/modget/query.go

@@ -239,10 +239,13 @@ func (q *query) matchesPath(path string) bool {
 // canMatchInModule reports whether the given module path can potentially
 // contain q.pattern.
 func (q *query) canMatchInModule(mPath string) bool {
+	if gover.IsToolchain(mPath) {
+		return false
+	}
 	if q.canMatchWildcardInModule != nil {
 		return q.canMatchWildcardInModule(mPath)
 	}
-	return str.HasPathPrefix(q.pattern, mPath) && !gover.IsToolchain(mPath)
+	return str.HasPathPrefix(q.pattern, mPath)
 }
 
 // pathOnce invokes f to generate the pathSet for the given path,

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

@@ -473,7 +473,11 @@ func newQueryMatcher(path string, query, current string, allowed AllowedFunc) (*
 // AllowedFunc of qm.
 func (qm *queryMatcher) allowsVersion(ctx context.Context, v string) bool {
 	if qm.prefix != "" && !strings.HasPrefix(v, qm.prefix) {
-		return false
+		if gover.IsToolchain(qm.path) && strings.TrimSuffix(qm.prefix, ".") == v {
+			// Allow 1.21 to match "1.21." prefix.
+		} else {
+			return false
+		}
 	}
 	if qm.filter != nil && !qm.filter(v) {
 		return false

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

@@ -1,34 +1,34 @@
 # setup
-env TESTGO_VERSION=go1.99.0
+env TESTGO_VERSION=go1.99rc1
 env TESTGO_VERSION_SWITCH=switch
 
 # go get go should use the latest Go 1.23
 cp go.mod.orig go.mod
 go get go
 stderr '^go: upgraded go 1.21 => 1.23.9$'
 grep 'go 1.23.9' go.mod
-grep 'toolchain go1.99.0' go.mod
+grep 'toolchain go1.99rc1' go.mod
 
 # go get go@1.23 should use the latest Go 1.23
 cp go.mod.orig go.mod
 go get go@1.23
 stderr '^go: upgraded go 1.21 => 1.23.9$'
 grep 'go 1.23.9' go.mod
-grep 'toolchain go1.99.0' go.mod
+grep 'toolchain go1.99rc1' go.mod
 
 # go get go@1.22 should use the latest Go 1.22
 cp go.mod.orig go.mod
 go get go@1.22
 stderr '^go: upgraded go 1.21 => 1.22.9$'
 grep 'go 1.22.9' go.mod
-grep 'toolchain go1.99.0' go.mod
+grep 'toolchain go1.99rc1' go.mod
 
 # go get go@patch should use the latest patch release
 go get go@1.22.1
 go get go@patch
 stderr '^go: upgraded go 1.22.1 => 1.22.9$'
 grep 'go 1.22.9' go.mod
-grep 'toolchain go1.99.0' go.mod
+grep 'toolchain go1.99rc1' go.mod
 
 # go get go@1.24 does NOT find the release candidate
 cp go.mod.orig go.mod
@@ -40,20 +40,20 @@ cp go.mod.orig go.mod
 go get go@1.24rc1
 stderr '^go: upgraded go 1.21 => 1.24rc1$'
 grep 'go 1.24rc1' go.mod
-grep 'toolchain go1.99.0' go.mod
+grep 'toolchain go1.99rc1' go.mod
 
 # go get go@latest finds the latest Go 1.23
 cp go.mod.orig go.mod
 go get go@latest
 stderr '^go: upgraded go 1.21 => 1.23.9$'
 grep 'go 1.23.9' go.mod
-grep 'toolchain go1.99.0' go.mod
+grep 'toolchain go1.99rc1' go.mod
 
 # Again, with toolchains.
 
 # go get toolchain should find go1.999testmod.
 go get toolchain
-stderr '^go: upgraded toolchain go1.99.0 => go1.999testmod$'
+stderr '^go: upgraded toolchain go1.99rc1 => go1.999testmod$'
 grep 'go 1.23.9' go.mod
 grep 'toolchain go1.999testmod' go.mod
 
@@ -96,6 +96,33 @@ stderr '^go: added toolchain go1.999testmod$'
 grep 'go 1.21' go.mod
 grep 'toolchain go1.999testmod' go.mod
 
+# Bug fixes.
+
+# go get go@garbage should fail but not crash
+! go get go@garbage
+! stderr panic
+stderr '^go: invalid go version garbage$'
+
+# go get go@go1.21.0 is OK - we silently correct to 1.21.0
+go get go@1.19
+go get go@go1.21.0
+stderr '^go: upgraded go 1.19 => 1.21.0'
+
+# go get toolchain@1.24rc1 is OK too.
+go get toolchain@1.24rc1
+stderr '^go: downgraded toolchain go1.999testmod => go1.24rc1$'
+
+# go get go@1.21 should work if we are the Go 1.21 language version,
+# even though there's no toolchain for it.
+# (Older versions resolve to the latest release in that version, so for example
+# go get go@1.20 might resolve to 1.20.9, but if we're the devel copy of
+# Go 1.21, there's no release yet to resolve to, so we resolve to ourselves.)
+env TESTGO_VERSION=go1.21
+go get go@1.19 toolchain@none
+go get go@1.21
+grep 'go 1.21$' go.mod
+! grep toolchain go.mod
+
 -- go.mod.orig --
 module m