Only run task once for #53

docs/usage.md

@@ -453,6 +453,41 @@ tasks:
       - echo "I will not run"
 ```
 
+### Limiting when tasks run
+
+If a task executed by multiple `cmds` or multiple `deps` you can limit
+how many times it is executed each invocation of the `task` command using `run`. `run` can also be set at the root of the taskfile to change the behavior of all the tasks unless explicitly overridden
+
+Supported values for `run`
+ * `always` (default) always attempt to invoke the task regardless of the number of previous executions
+ * `once` only invoke this task once regardless of the number of times referred to
+ * `when_changed` only invokes the task once for a set of variables passed into the task
+
+```yaml
+version: '3'
+tasks:
+  default:
+    cmds:
+      - task: generate-file
+        vars: { CONTENT: '1' }
+      - task: generate-file
+        vars: { CONTENT: '2' }
+      - task: generate-file
+        vars: { CONTENT: '2' }
+
+  generate-file:
+    run: when_changed
+    deps:
+      - install-deps
+    cmds:
+      - echo {{.CONTENT}}
+
+  install-deps:
+    run: once
+    cmds:
+      - sleep 5 # long operation like installing packages
+```
+
 ## Variables
 
 When doing interpolation of variables, Task will look for the below.

go.mod

@@ -5,6 +5,7 @@ require (
 	github.com/go-task/slim-sprig v0.0.0-20210107165309-348f09dbbbc0
 	github.com/joho/godotenv v1.3.0
 	github.com/mattn/go-zglob v0.0.3
+	github.com/mitchellh/hashstructure/v2 v2.0.2
 	github.com/radovskyb/watcher v1.0.7
 	github.com/spf13/pflag v1.0.5
 	github.com/stretchr/testify v1.7.0

go.sum

@@ -27,6 +27,8 @@ github.com/mattn/go-isatty v0.0.12 h1:wuysRhFDzyxgEmMf5xjvJ2M9dZoWAXNNr5LSBS7uHX
 github.com/mattn/go-isatty v0.0.12/go.mod h1:cbi8OIDigv2wuxKPP5vlRcQ1OAZbq2CE4Kysco4FUpU=
 github.com/mattn/go-zglob v0.0.3 h1:6Ry4EYsScDyt5di4OI6xw1bYhOqfE5S33Z1OPy+d+To=
 github.com/mattn/go-zglob v0.0.3/go.mod h1:9fxibJccNxU2cnpIKLRRFA7zX7qhkJIQWBb449FYHOo=
+github.com/mitchellh/hashstructure/v2 v2.0.2 h1:vGKWl0YJqUNxE8d+h8f6NJLcCJrgbhC4NcD46KavDd4=
+github.com/mitchellh/hashstructure/v2 v2.0.2/go.mod h1:MG3aRVU/N29oo/V/IhBX8GR/zz4kQkprJgF2EVszyDE=
 github.com/pkg/diff v0.0.0-20210226163009-20ebb0f2a09e/go.mod h1:pJLUxLENpZxwdsKMEsNbx1VGcRFpLqf3715MtcvvzbA=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=

hash.go

@@ -0,0 +1,28 @@
+package task
+
+import (
+	"fmt"
+
+	"github.com/go-task/task/v3/internal/hash"
+	"github.com/go-task/task/v3/taskfile"
+)
+
+func (e *Executor) GetHash(t *taskfile.Task) (string, error) {
+	r := t.Run
+	if r == "" {
+		r = e.Taskfile.Run
+	}
+
+	var h hash.HashFunc
+	switch r {
+	case "always":
+		h = hash.Empty
+	case "once":
+		h = hash.Name
+	case "when_changed":
+		h = hash.Hash
+	default:
+		return "", fmt.Errorf(`task: invalid run "%s"`, r)
+	}
+	return h(t)
+}

internal/hash/hash.go

@@ -0,0 +1,23 @@
+package hash
+
+import (
+	"fmt"
+
+	"github.com/go-task/task/v3/taskfile"
+	"github.com/mitchellh/hashstructure/v2"
+)
+
+type HashFunc func(*taskfile.Task) (string, error)
+
+func Empty(*taskfile.Task) (string, error) {
+	return "", nil
+}
+
+func Name(t *taskfile.Task) (string, error) {
+	return t.Task, nil
+}
+
+func Hash(t *taskfile.Task) (string, error) {
+	h, err := hashstructure.Hash(t, hashstructure.FormatV2, nil)
+	return fmt.Sprintf("%s:%d", t.Task, h), err
+}

task.go

@@ -58,6 +58,8 @@ type Executor struct {
 	concurrencySemaphore chan struct{}
 	taskCallCount        map[string]*int32
 	mkdirMutexMap        map[string]*sync.Mutex
+	execution            map[string]context.Context
+	executionMutex       sync.Mutex
 }
 
 // Run runs Task
@@ -225,6 +227,10 @@ func (e *Executor) Setup() error {
 		}
 	}
 
+	if e.Taskfile.Run == "" {
+		e.Taskfile.Run = "always"
+	}
+
 	if v <= 2.1 {
 		err := errors.New(`task: Taskfile option "ignore_error" is only available starting on Taskfile version v2.1`)
 
@@ -260,6 +266,8 @@ func (e *Executor) Setup() error {
 		}
 	}
 
+	e.execution = make(map[string]context.Context)
+
 	e.taskCallCount = make(map[string]*int32, len(e.Taskfile.Tasks))
 	e.mkdirMutexMap = make(map[string]*sync.Mutex, len(e.Taskfile.Tasks))
 	for k := range e.Taskfile.Tasks {
@@ -286,6 +294,17 @@ func (e *Executor) RunTask(ctx context.Context, call taskfile.Call) error {
 	release := e.acquireConcurrencyLimit()
 	defer release()
 
+	started, ctx, cancel, err := e.startExecution(ctx, t)
+	if err != nil {
+		return err
+	}
+	defer cancel()
+
+	if !started {
+		<-ctx.Done()
+		return nil
+	}
+
 	if err := e.runDeps(ctx, t); err != nil {
 		return err
 	}
@@ -445,3 +464,25 @@ func getEnviron(t *taskfile.Task) []string {
 
 	return environ
 }
+
+func (e *Executor) startExecution(innerCtx context.Context, t *taskfile.Task) (bool, context.Context, context.CancelFunc, error) {
+	h, err := e.GetHash(t)
+	if err != nil {
+		return true, nil, nil, err
+	}
+
+	if h == "" {
+		return true, innerCtx, func() {}, nil
+	}
+
+	e.executionMutex.Lock()
+	defer e.executionMutex.Unlock()
+	ctx, ok := e.execution[h]
+	if ok {
+		return false, ctx, func() {}, nil
+	}
+
+	ctx, cancel := context.WithCancel(innerCtx)
+	e.execution[h] = ctx
+	return true, ctx, cancel, nil
+}

task_test.go

@@ -979,3 +979,14 @@ func TestExitImmediately(t *testing.T) {
 	assert.Error(t, e.Run(context.Background(), taskfile.Call{Task: "default"}))
 	assert.Contains(t, buff.String(), `"this_should_fail": executable file not found in $PATH`)
 }
+
+func TestRunOnlyRunsJobsHashOnce(t *testing.T) {
+	tt := fileContentTest{
+		Dir:    "testdata/run",
+		Target: "generate-hash",
+		Files: map[string]string{
+			"hash.txt": "starting 1\n1\n2\n",
+		},
+	}
+	tt.Run(t)
+}

taskfile/task.go

@@ -22,6 +22,7 @@ type Task struct {
 	Method        string
 	Prefix        string
 	IgnoreError   bool
+	Run           string
 }
 
 func (t *Task) Name() string {
@@ -61,6 +62,7 @@ func (t *Task) UnmarshalYAML(unmarshal func(interface{}) error) error {
 		Method        string
 		Prefix        string
 		IgnoreError   bool `yaml:"ignore_error"`
+		Run           string
 	}
 	if err := unmarshal(&task); err != nil {
 		return err
@@ -81,5 +83,6 @@ func (t *Task) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	t.Method = task.Method
 	t.Prefix = task.Prefix
 	t.IgnoreError = task.IgnoreError
+	t.Run = task.Run
 	return nil
 }

taskfile/taskfile.go

@@ -17,6 +17,7 @@ type Taskfile struct {
 	Tasks      Tasks
 	Silent     bool
 	Dotenv     []string
+	Run        string
 }
 
 // UnmarshalYAML implements yaml.Unmarshaler interface
@@ -32,6 +33,7 @@ func (tf *Taskfile) UnmarshalYAML(unmarshal func(interface{}) error) error {
 		Tasks      Tasks
 		Silent     bool
 		Dotenv     []string
+		Run        string
 	}
 	if err := unmarshal(&taskfile); err != nil {
 		return err
@@ -46,6 +48,7 @@ func (tf *Taskfile) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	tf.Tasks = taskfile.Tasks
 	tf.Silent = taskfile.Silent
 	tf.Dotenv = taskfile.Dotenv
+	tf.Run = taskfile.Run
 	if tf.Expansions <= 0 {
 		tf.Expansions = 2
 	}

testdata/run/.gitignore

@@ -0,0 +1 @@
+*.txt

testdata/run/Taskfile.yml

@@ -0,0 +1,24 @@
+version: '3'
+run: when_changed
+
+tasks:
+  generate-hash:
+    - rm -f hash.txt
+    - task: input-content
+      vars: { CONTENT: '1' }
+    - task: input-content
+      vars: { CONTENT: '2' }
+    - task: input-content
+      vars: { CONTENT: '2' }
+
+  input-content:
+    deps:
+      - task: create-output
+        vars: { CONTENT: '1' }
+    cmds:
+      - echo {{.CONTENT}} >> hash.txt
+
+  create-output:
+    run: once
+    cmds:
+      - echo starting {{.CONTENT}} >> hash.txt

variables.go

@@ -59,6 +59,7 @@ func (e *Executor) compiledTask(call taskfile.Call, evaluateShVars bool) (*taskf
 		Method:      r.Replace(origTask.Method),
 		Prefix:      r.Replace(origTask.Prefix),
 		IgnoreError: origTask.IgnoreError,
+		Run:         r.Replace(origTask.Run),
 	}
 	new.Dir, err = execext.Expand(new.Dir)
 	if err != nil {