cmd/go: install binaries in cmd/ in $GOROOT/bin instead of $GOBIN

This was caused by CL 167748, which removed a special case for command
line arguments starting with "cmd/". This CL restores the behavior
from go1.12.

Fixes #32674

Change-Id: I72180d11fb0261ef0af9632e512bd9c03481b6c0
Reviewed-on: https://go-review.googlesource.com/c/go/+/183058
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

src/cmd/go/internal/load/pkg.go

@@ -662,11 +662,17 @@ func loadPackageData(path, parentPath, parentDir, parentRoot string, parentIsStd
 			data.p, data.err = cfg.BuildContext.Import(r.path, parentDir, buildMode)
 		}
 		data.p.ImportPath = r.path
-		if cfg.GOBIN != "" {
-			data.p.BinDir = cfg.GOBIN
-		} else if cfg.ModulesEnabled && !data.p.Goroot {
-			data.p.BinDir = ModBinDir()
+
+		// Set data.p.BinDir in cases where go/build.Context.Import
+		// may give us a path we don't want.
+		if !data.p.Goroot {
+			if cfg.GOBIN != "" {
+				data.p.BinDir = cfg.GOBIN
+			} else if cfg.ModulesEnabled {
+				data.p.BinDir = ModBinDir()
+			}
 		}
+
 		if !cfg.ModulesEnabled && data.err == nil &&
 			data.p.ImportComment != "" && data.p.ImportComment != path &&
 			!strings.Contains(path, "/vendor/") && !strings.HasPrefix(path, "vendor/") {

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

@@ -0,0 +1,10 @@
+# Check that commands in cmd are install to $GOROOT/bin, not $GOBIN.
+# Verifies golang.org/issue/32674.
+env GOBIN=gobin
+mkdir gobin
+go list -f '{{.Target}}' cmd/go
+stdout $GOROOT[/\\]bin[/\\]go$GOEXE
+
+# Check that tools are installed to $GOTOOLDIR, not $GOBIN.
+go list -f '{{.Target}}' cmd/compile
+stdout $GOROOT[/\\]pkg[/\\]tool[/\\]${GOOS}_${GOARCH}[/\\]compile$GOEXE