cmd/dist: move "devel" substring in git-inferred development version

Keep the property that the "devel" substring is always present in these
development versions of Go, but also gain the property that it's viable
to use functions in the go/version package such as Lang, Compare, and
get the expected results without needing to trim the "devel " prefix.

For #73369.
For #41116.
Fixes #73372.

Change-Id: Ieea4692e8c6cf0135e010f49f85300f6b038d6b1
Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-longtest
Reviewed-on: https://go-review.googlesource.com/c/go/+/668015
Reviewed-by: Funda Secgin <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Auto-Submit: Dmitri Shuralyov <[email protected]>
Reviewed-by: Michael Pratt <[email protected]>

Author: dmitshur

src/cmd/dist/build.go

@@ -426,6 +426,10 @@ func findgoversion() string {
 	// Otherwise, use Git.
 	//
 	// Include 1.x base version, hash, and date in the version.
+	// Make sure it includes the substring "devel", but otherwise
+	// use a format compatible with https://go.dev/doc/toolchain#name
+	// so that it's possible to use go/version.Lang, Compare and so on.
+	// See go.dev/issue/73372.
 	//
 	// Note that we lightly parse internal/goversion/goversion.go to
 	// obtain the base version. We can't just import the package,
@@ -437,7 +441,7 @@ func findgoversion() string {
 	if m == nil {
 		fatalf("internal/goversion/goversion.go does not contain 'const Version = ...'")
 	}
-	version := fmt.Sprintf("devel go1.%s-", m[1])
+	version := fmt.Sprintf("go1.%s-devel_", m[1])
 	version += chomp(run(goroot, CheckExit, "git", "log", "-n", "1", "--format=format:%h %cd", "HEAD"))
 
 	// Cache version.