New Flag: -nodeps: skip target dependencies when executing target

mage/main.go

@@ -100,6 +100,7 @@ type Invocation struct {
 	List       bool          // tells the magefile to print out a list of targets
 	Help       bool          // tells the magefile to print out help for a specific target
 	Keep       bool          // tells mage to keep the generated main file after compiling
+	NoDeps     bool          // tells mage to execute the given target without dependencies
 	Timeout    time.Duration // tells mage to set a timeout to running the targets
 	CompileOut string        // tells mage to compile a static binary to this path, but not execute
 	GOOS       string        // sets the GOOS when producing a binary with -compileout
@@ -174,6 +175,7 @@ func Parse(stderr, stdout io.Writer, args []string) (inv Invocation, cmd Command
 	fs.BoolVar(&inv.Help, "h", false, "show this help")
 	fs.DurationVar(&inv.Timeout, "t", 0, "timeout in duration parsable format (e.g. 5m30s)")
 	fs.BoolVar(&inv.Keep, "keep", false, "keep intermediate mage files around after running")
+	fs.BoolVar(&inv.NoDeps, "nodeps", false, "execute the given target without it's dependencies")
 	fs.StringVar(&inv.Dir, "d", ".", "run magefiles in the given directory")
 	fs.StringVar(&inv.GoCmd, "gocmd", mg.GoCmd(), "use the given go binary to compile the output")
 	fs.StringVar(&inv.GOOS, "goos", "", "set GOOS for binary produced with -compile")
@@ -213,6 +215,7 @@ Options:
   -h        show description of a target
   -f        force recreation of compiled magefile
   -keep     keep intermediate mage files around after running
+  -nodeps   execute the given target without it's dependencies
   -gocmd <string>
 		    use the given go binary to compile the output (default: "go")
   -goos     sets the GOOS for the binary created by -compile (default: current OS)
@@ -625,6 +628,9 @@ func RunCompiled(inv Invocation, exePath string, errlog *log.Logger) int {
 	if inv.Timeout > 0 {
 		c.Env = append(c.Env, fmt.Sprintf("MAGEFILE_TIMEOUT=%s", inv.Timeout.String()))
 	}
+	if inv.NoDeps {
+		c.Env = append(c.Env, "MAGEFILE_NODEPS=1")
+	}
 	debug.Print("running magefile with mage vars:\n", strings.Join(filter(c.Env, "MAGEFILE"), "\n"))
 	err := c.Run()
 	if !sh.CmdRan(err) {

mg/deps.go

@@ -92,6 +92,10 @@ func CtxDeps(ctx context.Context, fns ...interface{}) {
 
 // runDeps assumes you've already called checkFns.
 func runDeps(ctx context.Context, types []funcType, fns []interface{}) {
+	if os.Getenv(NoDepsEnv) == "1" {
+		return
+	}
+
 	mu := &sync.Mutex{}
 	var errs []string
 	var exit int

mg/deps_test.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"log"
+	"os"
 	"testing"
 	"time"
 )
@@ -192,3 +193,62 @@ func TestDepsErrors(t *testing.T) {
 	}()
 	f()
 }
+
+func TestDepsWithNoDepsSet(t *testing.T) {
+	if err := os.Setenv(NoDepsEnv, "1"); err != nil {
+		t.Fatalf("Failed to set %s for test", NoDepsEnv)
+	}
+	defer func() {
+		if err := os.Unsetenv(NoDepsEnv); err != nil {
+			t.Fatalf("Failed to clear %s after test", NoDepsEnv)
+		}
+	}()
+
+	ch := make(chan string, 3)
+	// this->f->g->h
+	h := func() {
+		ch <- "h"
+	}
+	g := func() {
+		Deps(h)
+		ch <- "g"
+	}
+	f := func() {
+		Deps(g)
+		ch <- "f"
+	}
+	Deps(f)
+
+	if len(ch) != 0 {
+		t.Errorf("Expected no deps to run but %d ran", len(ch))
+	}
+}
+
+func TestSerialDepsWithNoDepsSet(t *testing.T) {
+	if err := os.Setenv(NoDepsEnv, "1"); err != nil {
+		t.Fatalf("Failed to set %s for test", NoDepsEnv)
+	}
+	defer func() {
+		if err := os.Unsetenv(NoDepsEnv); err != nil {
+			t.Fatalf("Failed to clear %s after test", NoDepsEnv)
+		}
+	}()
+
+	ch := make(chan string, 3)
+	// this->f->g->h
+	h := func() {
+		ch <- "h"
+	}
+	g := func() {
+		ch <- "g"
+	}
+	f := func() {
+		SerialDeps(g, h)
+		ch <- "f"
+	}
+	Deps(f)
+
+	if len(ch) != 0 {
+		t.Errorf("Expected no deps to run but %d ran", len(ch))
+	}
+}

mg/runtime.go

@@ -27,6 +27,10 @@ const GoCmdEnv = "MAGEFILE_GOCMD"
 // to ignore the default target specified in the magefile.
 const IgnoreDefaultEnv = "MAGEFILE_IGNOREDEFAULT"
 
+// NoDepsEnv is the environment variable that indicates the user requested
+// that dependencies of the target not be executed
+const NoDepsEnv = "MAGEFILE_NODEPS"
+
 // Verbose reports whether a magefile was run with the verbose flag.
 func Verbose() bool {
 	b, _ := strconv.ParseBool(os.Getenv(VerboseEnv))

site/content/dependencies/_index.en.md

@@ -72,3 +72,13 @@ Build running
 Note that since f and g do not depend on each other, and they're running in
 their own goroutines, their order is non-deterministic, other than they are
 guaranteed to run after h has finished, and before Build continues.
+
+### Skipping Dependencies
+
+You can tell mage to execute a target but not its dependencies by passing
+the `-nodeps` flag when running mage. Using the example above, running
+`mage -nodeps build` will produce the following output:
+
+```bash
+Build running
+```