cmd/go: respect $GOBIN always

Another attempt at https://golang.org/cl/5754088.

Before, we only consulted $GOBIN for source code
found in $GOROOT, but that's confusing to explain
and less useful.  The new behavior lets users set
GOBIN=$HOME/bin and have all go-compiled binaries
installed there.

Tested a few cases in test.bash.

Ran all.bash with and without $GOBIN and it works.
Even so, I expect it to break the builders,
like it did last time, we can debug from there.

Fixes #3269 (again).
Fixes #3396.
Fixes #3397.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/5927051

doc/install-source.html

@@ -393,11 +393,12 @@ For example, you should not set <code>$GOHOSTARCH</code> to
 
 <p><code>$GOBIN</code>
 <p>
-The location where binaries from the main repository will be installed.
-XXX THIS MAY CHANGE TO BE AN OVERRIDE EVEN FOR GOPATH ENTRIES XXX
+The location where Go binaries will be installed.
 The default is <code>$GOROOT/bin</code>.
 After installing, you will want to arrange to add this
 directory to your <code>$PATH</code>, so you can use the tools.
+If <code>$GOBIN</code> is set, the <a href="/cmd/go">go command</a>
+installs all commands there.
 </p>
 
 <p><code>$GOARM</code> (arm, default=6)</p>

src/cmd/go/build.go

@@ -74,6 +74,8 @@ The build flags are shared by the build, install, run, and test commands:
 		more information about build tags.
 
 For more about specifying packages, see 'go help packages'.
+For more about where packages and binaries are installed,
+see 'go help gopath'.
 
 See also: go install, go get, go clean.
 	`,
@@ -304,19 +306,13 @@ const (
 
 var (
 	goroot       = filepath.Clean(runtime.GOROOT())
-	gobin        = defaultGobin()
+	gobin        = os.Getenv("GOBIN")
+	gorootBin    = filepath.Join(goroot, "bin")
 	gorootSrcPkg = filepath.Join(goroot, "src/pkg")
 	gorootPkg    = filepath.Join(goroot, "pkg")
 	gorootSrc    = filepath.Join(goroot, "src")
 )
 
-func defaultGobin() string {
-	if s := os.Getenv("GOBIN"); s != "" {
-		return s
-	}
-	return filepath.Join(goroot, "bin")
-}
-
 func (b *builder) init() {
 	var err error
 	b.print = fmt.Print
@@ -388,17 +384,23 @@ func goFilesPackage(gofiles []string) *Package {
 	pkg.load(&stk, bp, err)
 	pkg.localPrefix = dirToImportPath(dir)
 	pkg.ImportPath = "command-line-arguments"
+	pkg.target = ""
 
-	if *buildO == "" {
 	if pkg.Name == "main" {
 		_, elem := filepath.Split(gofiles[0])
-			*buildO = elem[:len(elem)-len(".go")] + exeSuffix
+		exe := elem[:len(elem)-len(".go")] + exeSuffix
+		if *buildO == "" {
+			*buildO = exe
+		}
+		if gobin != "" {
+			pkg.target = filepath.Join(gobin, exe)
+		}
 	} else {
+		if *buildO == "" {
 			*buildO = pkg.Name + ".a"
 		}
 	}
-	pkg.target = ""
-	pkg.Target = ""
+	pkg.Target = pkg.target
 	pkg.Stale = true
 
 	computeStale(pkg)
@@ -463,7 +465,7 @@ func (b *builder) action(mode buildMode, depMode buildMode, p *Package) *action
 		return a
 	}
 
-	if p.local {
+	if p.local && p.target == "" {
 		// Imported via local path.  No permanent target.
 		mode = modeBuild
 	}

src/cmd/go/doc.go

@@ -91,6 +91,8 @@ The build flags are shared by the build, install, run, and test commands:
 		more information about build tags.
 
 For more about specifying packages, see 'go help packages'.
+For more about where packages and binaries are installed,
+see 'go help gopath'.
 
 See also: go install, go get, go clean.
 
@@ -461,7 +463,9 @@ the final element, not the entire path.  That is, the
 command with source in DIR/src/foo/quux is installed into
 DIR/bin/quux, not DIR/bin/foo/quux.  The foo/ is stripped
 so that you can add DIR/bin to your PATH to get at the
-installed commands.
+installed commands.  If the GOBIN environment variable is
+set, commands are installed to the directory it names instead
+of DIR/bin.
 
 Here's an example directory layout:
 

src/cmd/go/help.go

@@ -209,7 +209,9 @@ the final element, not the entire path.  That is, the
 command with source in DIR/src/foo/quux is installed into
 DIR/bin/quux, not DIR/bin/foo/quux.  The foo/ is stripped
 so that you can add DIR/bin to your PATH to get at the
-installed commands.
+installed commands.  If the GOBIN environment variable is
+set, commands are installed to the directory it names instead
+of DIR/bin.
 
 Here's an example directory layout:
 

src/cmd/go/pkg.go

@@ -222,6 +222,9 @@ func loadImport(path string, srcDir string, stk *importStack, importPos []token.
 	// See issue 3268 for mistakes to avoid.
 	bp, err := buildContext.Import(path, srcDir, 0)
 	bp.ImportPath = importPath
+	if gobin != "" {
+		bp.BinDir = gobin
+	}
 	p.load(stk, bp, err)
 	if p.Error != nil && len(importPos) > 0 {
 		pos := importPos[0]
@@ -552,7 +555,10 @@ func loadPackage(arg string, stk *importStack) *Package {
 		bp, err := build.ImportDir(filepath.Join(gorootSrc, arg), 0)
 		bp.ImportPath = arg
 		bp.Goroot = true
+		bp.BinDir = gorootBin
+		if gobin != "" {
 			bp.BinDir = gobin
+		}
 		bp.Root = goroot
 		bp.SrcRoot = gorootSrc
 		p := new(Package)

src/cmd/go/test.bash

@@ -8,6 +8,9 @@ go build -o testgo
 
 ok=true
 
+unset GOPATH
+unset GOBIN
+
 # Test that error messages have file:line information
 # at beginning of line.
 for i in testdata/errmsg/*.go
@@ -80,6 +83,42 @@ if ! ./testgo test ./testdata/testimport/*.go; then
 	ok=false
 fi
 
+# Test that without $GOBIN set, binaries get installed
+# into the GOPATH bin directory.
+rm -rf testdata/bin
+if ! GOPATH=$(pwd)/testdata ./testgo install go-cmd-test; then
+	echo "go install go-cmd-test failed"
+	ok=false
+elif ! test -x testdata/bin/go-cmd-test; then
+	echo "go install go-cmd-test did not write to testdata/bin/go-cmd-test"
+	ok=false
+fi
+
+# And with $GOBIN set, binaries get installed to $GOBIN.
+if ! GOBIN=$(pwd)/testdata/bin1 GOPATH=$(pwd)/testdata ./testgo install go-cmd-test; then
+	echo "go install go-cmd-test failed"
+	ok=false
+elif ! test -x testdata/bin1/go-cmd-test; then
+	echo "go install go-cmd-test did not write to testdata/bin1/go-cmd-test"
+	ok=false
+fi
+
+# Without $GOBIN set, installing a program outside $GOPATH should fail
+# (there is nowhere to install it).
+if ./testgo install testdata/src/go-cmd-test/helloworld.go; then
+	echo "go install testdata/src/go-cmd-test/helloworld.go should have failed, did not"
+	ok=false
+fi
+
+# With $GOBIN set, should install there.
+if ! GOBIN=$(pwd)/testdata/bin1 ./testgo install testdata/src/go-cmd-test/helloworld.go; then
+	echo "go install testdata/src/go-cmd-test/helloworld.go failed"
+	ok=false
+elif ! test -x testdata/bin1/helloworld; then
+	echo "go install testdata/src/go-cmd-test/helloworld.go did not write testdata/bin1/helloworld"
+	ok=false
+fi
+
 if $ok; then
 	echo PASS
 else

src/cmd/go/testdata/src/go-cmd-test/helloworld.go

+package main
+
+func main() {
+	println("hello world")
+}