goinstall: process dependencies for package main

Currently to install a command, you have to manually
goinstall each of the remote packages that it depends on.
This patch lets goinstall P work where P is
contains files in package main.
It does not actually build the package, but
it installs all of its dependencies and prints a message
to that effect.

R=rsc
CC=golang-dev
https://golang.org/cl/1301043

src/cmd/goinstall/main.go

diff --git a/src/cmd/goinstall/main.go b/src/cmd/goinstall/main.go
index 59e6628..ecd2153 100644
--- a/src/cmd/goinstall/main.go
+++ b/src/cmd/goinstall/main.go
@@ -122,7 +122,7 @@
 	}
 
 	// Install prerequisites.
-	files, m, err := goFiles(dir)
+	files, m, pkgname, err := goFiles(dir, parent == "")
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "%s: %s: %s\n", argv0, pkg, err)
 		errors = true
@@ -138,6 +138,14 @@
 	for p := range m {
 		install(p, pkg)
 	}
+	if pkgname == "main" {
+		if !errors {
+			fmt.Fprintf(os.Stderr, "%s: %s's dependencies are installed.\n", argv0, pkg)
+		}
+		errors = true
+		visit[pkg] = done
+		return
+	}
 
 	// Install this package.
 	if !errors {

src/cmd/goinstall/make.go

diff --git a/src/cmd/goinstall/make.go b/src/cmd/goinstall/make.go
index 59fc332..c15709b3 100644
--- a/src/cmd/goinstall/make.go
+++ b/src/cmd/goinstall/make.go
@@ -35,11 +35,10 @@
 // installing as package pkg.  It includes all *.go files in the directory
 // except those in package main and those ending in _test.go.
 func makeMakefile(dir, pkg string) ([]byte, os.Error) {
-	files, _, err := goFiles(dir)
+	files, _, _, err := goFiles(dir, false)
 	if err != nil {
 		return nil, err
 	}
-
 	var buf bytes.Buffer
 	if err := makefileTemplate.Execute(&makedata{pkg, files}, &buf); err != nil {
 		return nil, err

src/cmd/goinstall/parse.go

diff --git a/src/cmd/goinstall/parse.go b/src/cmd/goinstall/parse.go
index 066c47f..ae391ed 100644
--- a/src/cmd/goinstall/parse.go
+++ b/src/cmd/goinstall/parse.go
@@ -16,25 +16,25 @@
 	"go/parser"
 )
 
-// goFiles returns a list of the *.go source files in dir,
-// excluding those in package main or ending in _test.go.
-// It also returns a map giving the packages imported
-// by those files.  The map keys are the imported paths.
-// The key's value is one file that imports that path.
-func goFiles(dir string) (files []string, imports map[string]string, err os.Error) {
+// goFiles returns a list of the *.go source files in dir, excluding
+// those in package main (unless allowMain is true) or ending in
+// _test.go.  It also returns a map giving the packages imported by
+// those files, and the package name.
+// The map keys are the imported paths.  The key's value
+// is one file that imports that path.
+func goFiles(dir string, allowMain bool) (files []string, imports map[string]string, pkgName string, err os.Error) {
 	f, err := os.Open(dir, os.O_RDONLY, 0)
 	if err != nil {
-		return nil, nil, err
+		return nil, nil, "", err
 	}
 	dirs, err := f.Readdir(-1)
 	f.Close()
 	if err != nil {
-		return nil, nil, err
+		return nil, nil, "", err
 	}
 
 	files = make([]string, 0, len(dirs))
 	imports = make(map[string]string)
-	pkgName := ""
 	for i := range dirs {
 		d := &dirs[i]
 		if !strings.HasSuffix(d.Name, ".go") || strings.HasSuffix(d.Name, "_test.go") {
@@ -43,16 +43,23 @@
 		filename := path.Join(dir, d.Name)
 		pf, err := parser.ParseFile(filename, nil, nil, parser.ImportsOnly)
 		if err != nil {
-			return nil, nil, err
+			return nil, nil, "", err
 		}
 		s := string(pf.Name.Name())
-		if s == "main" {
+		if s == "main" && !allowMain {
 			continue
 		}
 		if pkgName == "" {
 			pkgName = s
 		} else if pkgName != s {
-			return nil, nil, os.ErrorString("multiple package names in " + dir)
+			// Only if all files in the directory are in package main
+			// do we return pkgName=="main".
+			// A mix of main and another package reverts
+			// to the original (allowMain=false) behaviour.
+			if allowMain && pkgName == "main" {
+				return goFiles(dir, false)
+			}
+			return nil, nil, "", os.ErrorString("multiple package names in " + dir)
 		}
 		n := len(files)
 		files = files[0 : n+1]
@@ -68,5 +75,5 @@
 			}
 		}
 	}
-	return files, imports, nil
+	return files, imports, pkgName, nil
 }