cmd/go: when expanding "cmd", skip vendored main packages

We are vendoring pprof from github.com/google/pprof, which comes with
a main package. If we don't explicitly skip that main package, then
`go install cmd` will install the compiled program in $GOROOT/bin.

Fixes #19441.

Change-Id: Ib268ffd16d4be65f7d80e4f8d9dc6e71523a94de
Reviewed-on: https://go-review.googlesource.com/38007
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Raul Silvera <rsilvera@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/go/internal/load/search.go

@@ -93,12 +93,21 @@ func MatchPackages(pattern string) []string {
 			if !match(name) {
 				return nil
 			}
-			_, err = cfg.BuildContext.ImportDir(path, 0)
+			pkg, err := cfg.BuildContext.ImportDir(path, 0)
 			if err != nil {
 				if _, noGo := err.(*build.NoGoError); noGo {
 					return nil
 				}
 			}
+
+			// If we are expanding "cmd", skip main
+			// packages under cmd/vendor. At least as of
+			// March, 2017, there is one there for the
+			// vendored pprof tool.
+			if pattern == "cmd" && strings.HasPrefix(pkg.ImportPath, "cmd/vendor") && pkg.Name == "main" {
+				return nil
+			}
+
 			pkgs = append(pkgs, name)
 			return nil
 		})

src/make.bash

@@ -172,7 +172,20 @@ if [ "$GOHOSTARCH" != "$GOARCH" -o "$GOHOSTOS" != "$GOOS" ]; then
 fi
 
 echo "##### Building packages and commands for $GOOS/$GOARCH."
+
+old_bin_files=$(cd $GOROOT/bin && echo *)
+
 CC=$CC_FOR_TARGET "$GOTOOLDIR"/go_bootstrap install $GO_FLAGS -gcflags "$GO_GCFLAGS" -ldflags "$GO_LDFLAGS" -v std cmd
+
+# Check that there are no new files in $GOROOT/bin other than go and gofmt
+# and $GOOS_$GOARCH (a directory used when cross-compiling).
+(cd $GOROOT/bin && for f in *; do
+	if ! expr " $old_bin_files go gofmt ${GOOS}_${GOARCH} " : ".* $f " >/dev/null 2>/dev/null; then
+		echo 1>&2 "ERROR: unexpected new file in $GOROOT/bin: $f"
+		exit 1
+	fi
+done)
+
 echo
 
 rm -f "$GOTOOLDIR"/go_bootstrap