bake: load .env file from working dir for compose files

Signed-off-by: CrazyMax <[email protected]>

bake/compose.go

@@ -2,8 +2,11 @@ package bake
 
 import (
 	"fmt"
+	"os"
+	"path/filepath"
 	"strings"
 
+	"github.com/compose-spec/compose-go/dotenv"
 	"github.com/compose-spec/compose-go/loader"
 	compose "github.com/compose-spec/compose-go/types"
 	"github.com/pkg/errors"
@@ -14,6 +17,10 @@ import (
 var errComposeInvalid = errors.New("invalid compose file")
 
 func ParseCompose(dt []byte, envs map[string]string) (*Config, error) {
+	if wd, err := os.Getwd(); err == nil {
+		envs = loadDotEnv(envs, wd)
+	}
+
 	cfg, err := loader.Load(compose.ConfigDetails{
 		ConfigFiles: []compose.ConfigFile{
 			{
@@ -28,6 +35,7 @@ func ParseCompose(dt []byte, envs map[string]string) (*Config, error) {
 	if err != nil {
 		return nil, err
 	}
+
 	if err = composeValidate(cfg); err != nil {
 		return nil, err
 	}
@@ -107,6 +115,41 @@ func ParseCompose(dt []byte, envs map[string]string) (*Config, error) {
 	return &c, nil
 }
 
+func loadDotEnv(currentEnv map[string]string, workingDir string) map[string]string {
+	if currentEnv == nil {
+		currentEnv = make(map[string]string)
+	}
+
+	ef, err := filepath.Abs(filepath.Join(workingDir, ".env"))
+	if err != nil {
+		return currentEnv
+	}
+
+	if _, err := os.Stat(ef); err != nil {
+		return currentEnv
+	}
+
+	file, err := os.Open(ef)
+	if err != nil {
+		return currentEnv
+	}
+	defer file.Close()
+
+	envs, err := dotenv.Parse(file)
+	if err != nil {
+		return currentEnv
+	}
+
+	for k, v := range envs {
+		if _, set := currentEnv[k]; set {
+			continue
+		}
+		currentEnv[k] = v
+	}
+
+	return currentEnv
+}
+
 func flatten(in compose.MappingWithEquals) compose.Mapping {
 	if len(in) == 0 {
 		return nil

bake/compose_test.go

@@ -2,6 +2,7 @@ package bake
 
 import (
 	"os"
+	"path/filepath"
 	"sort"
 	"testing"
 
@@ -380,6 +381,27 @@ services:
 	require.Equal(t, map[string]string{"CT_ECR": "foo", "FOO": "bsdf -csdf", "NODE_ENV": "test"}, c.Targets[0].Args)
 }
 
+func TestDotEnv(t *testing.T) {
+	tmpdir := t.TempDir()
+
+	err := os.WriteFile(filepath.Join(tmpdir, ".env"), []byte("FOO=bar"), 0644)
+	require.NoError(t, err)
+
+	var dt = []byte(`
+services:
+  scratch:
+    build:
+     context: .
+     args:
+        FOO:
+`)
+
+	chdir(t, tmpdir)
+	c, err := ParseCompose(dt, nil)
+	require.NoError(t, err)
+	require.Equal(t, map[string]string{"FOO": "bar"}, c.Targets[0].Args)
+}
+
 func TestPorts(t *testing.T) {
 	var dt = []byte(`
 services:
@@ -523,3 +545,21 @@ services:
 		})
 	}
 }
+
+// chdir changes the current working directory to the named directory,
+// and then restore the original working directory at the end of the test.
+func chdir(t *testing.T, dir string) {
+	olddir, err := os.Getwd()
+	if err != nil {
+		t.Fatalf("chdir: %v", err)
+	}
+	if err := os.Chdir(dir); err != nil {
+		t.Fatalf("chdir %s: %v", dir, err)
+	}
+	t.Cleanup(func() {
+		if err := os.Chdir(olddir); err != nil {
+			t.Errorf("chdir to original working directory %s: %v", olddir, err)
+			os.Exit(1)
+		}
+	})
+}

docs/guides/bake/configuring-build.md

@@ -190,6 +190,55 @@ $ TAG=v1.2.0 docker buildx bake -f docker-bake.hcl -f prod.env --print
 }
 ```
 
+### `.env` file 
+
+You can declare default environment variables in an environment file named
+`.env`. This file will be loaded from the current working directory,
+where the command is executed and applied to [compose definitions](compose-file.md).
+
+```yaml
+# docker-compose.yml
+services:
+  webapp:
+    image: docker.io/username/webapp:${TAG:-v1.0.0}
+    build:
+      dockerfile: Dockerfile
+```
+
+```
+# .env
+TAG=v1.1.0
+```
+
+```console
+$ docker buildx bake --print
+```
+```json
+{
+  "group": {
+    "default": {
+      "targets": [
+        "webapp"
+      ]
+    }
+  },
+  "target": {
+    "webapp": {
+      "context": ".",
+      "dockerfile": "Dockerfile",
+      "tags": [
+        "docker.io/username/webapp:v1.1.0"
+      ]
+    }
+  }
+}
+```
+
+> **Note**
+>
+> System environment variables and environment variables defined in `-f` take
+> precedence over environment variables in `.env`.
+
 ## From command line
 
 You can also override target configurations from the command line with the