cmd/go: run main package when no files are listed

Fixes 5164.

R=golang-dev, iant, adg
CC=golang-dev
https://golang.org/cl/8119049

doc/go1.1.html

@@ -392,6 +392,15 @@ To update pre-Go 1 code to Go 1.1, use a Go 1.0 tool chain
 to convert the code to Go 1.0 first.
 </p>
 
+<h3 id="gorun">Changes to the go run command</h3>
+
+<p>
+The <code>go run</code> command now runs all files in the current working
+directory if no file arguments are listed. Also, the <code>go run</code>
+command now returns an error if test files are provided on the command line. In
+this sense, "<code>go run</code>" replaces "<code>go run *.go</code>".
+</p>
+
 <h3 id="platforms">Additional platforms</h3>
 
 <p>

src/cmd/go/doc.go

@@ -367,9 +367,10 @@ Compile and run Go program
 
 Usage:
 
-	go run [build flags] gofiles... [arguments...]
+	go run [build flags] [gofiles...] [arguments...]
 
 Run compiles and runs the main package comprising the named Go source files.
+If no files are named, it compiles and runs all non-test Go source files.
 
 For more about build flags, see 'go help build'.
 

src/cmd/go/run.go

@@ -8,14 +8,16 @@ import (
 	"fmt"
 	"os"
 	"os/exec"
+	"path/filepath"
 	"strings"
 )
 
 var cmdRun = &Command{
-	UsageLine: "run [build flags] gofiles... [arguments...]",
+	UsageLine: "run [build flags] [gofiles...] [arguments...]",
 	Short:     "compile and run Go program",
 	Long: `
 Run compiles and runs the main package comprising the named Go source files.
+If no files are named, it compiles and runs all non-test Go source files.
 
 For more about build flags, see 'go help build'.
 
@@ -44,7 +46,18 @@ func runRun(cmd *Command, args []string) {
 	}
 	files, cmdArgs := args[:i], args[i:]
 	if len(files) == 0 {
-		fatalf("go run: no go files listed")
+		allFiles, err := filepath.Glob("*.go")
+		if err != nil {
+			fatalf("go run: %s", err)
+		}
+		for _, file := range allFiles {
+			if !strings.HasSuffix(file, "_test.go") {
+				files = append(files, file)
+			}
+		}
+		if len(files) == 0 {
+			fatalf("go run: no go files found")
+		}
 	}
 	for _, file := range files {
 		if strings.HasSuffix(file, "_test.go") {