Add experimental way to set a target platform when building

Add an --experimental-platform flag to the do command to allow
overriding the default auto-detected build platform until we find the
time to think about the definitive multi-platform builds UX

Signed-off-by: Marcos Lilljedahl <marcosnils@gmail.com>

client/client.go

@@ -44,6 +44,8 @@ type Config struct {
 
 	CacheExports []bk.CacheOptionsEntry
 	CacheImports []bk.CacheOptionsEntry
+
+	TargetPlatform *specs.Platform
 }
 
 func New(ctx context.Context, host string, cfg Config) (*Client, error) {
@@ -81,8 +83,9 @@ func (c *Client) Do(ctx context.Context, pctx *plancontext.Context, fn DoFunc) e
 	lg := log.Ctx(ctx)
 	eg, gctx := errgroup.WithContext(ctx)
 
-	// if platform is set through plan config, skip detection.
-	if !pctx.Platform.IsSet() {
+	if c.cfg.TargetPlatform != nil {
+		pctx.Platform.Set(*c.cfg.TargetPlatform)
+	} else {
 		p, err := c.detectPlatform(ctx)
 		if err != nil {
 			return err

cmd/dagger/cmd/common/common.go

@@ -6,7 +6,9 @@ import (
 	"strings"
 
 	"cuelang.org/go/cue"
+	"github.com/containerd/containerd/platforms"
 	"github.com/docker/buildx/util/buildflags"
+	specs "github.com/opencontainers/image-spec/specs-go/v1"
 	"github.com/rs/zerolog/log"
 	"github.com/spf13/viper"
 	"go.dagger.io/dagger/client"
@@ -95,10 +97,21 @@ func NewClient(ctx context.Context) *client.Client {
 		lg.Fatal().Err(err).Msg("unable to parse --cache-from options")
 	}
 
+	ep := viper.GetString("experimental-platform")
+	var p *specs.Platform
+	if len(ep) > 0 {
+		pp, err := platforms.Parse(ep)
+		if err != nil {
+			lg.Fatal().Err(err).Msg("invalid value for --experimental-platform")
+		}
+		p = &pp
+	}
+
 	cl, err := client.New(ctx, "", client.Config{
-		CacheExports: cacheExports,
-		CacheImports: cacheImports,
-		NoCache:      viper.GetBool("no-cache"),
+		CacheExports:   cacheExports,
+		CacheImports:   cacheImports,
+		NoCache:        viper.GetBool("no-cache"),
+		TargetPlatform: p,
 	})
 	if err != nil {
 		lg.Fatal().Err(err).Msg("unable to create client")

cmd/dagger/cmd/do.go

@@ -157,6 +157,7 @@ func init() {
 	doCmd.Flags().StringArrayP("with", "w", []string{}, "")
 	doCmd.Flags().StringP("plan", "p", ".", "Path to plan (defaults to current directory)")
 	doCmd.Flags().Bool("no-cache", false, "Disable caching")
+	doCmd.Flags().String("experimental-platform", "", "Set target build platform (experimental)")
 	doCmd.Flags().StringArray("cache-to", []string{},
 		"Cache export destinations (eg. user/app:cache, type=local,dest=path/to/dir)")
 	doCmd.Flags().StringArray("cache-from", []string{},

plancontext/platform.go

@@ -25,7 +25,3 @@ func (c *platformContext) SetString(platform string) error {
 func (c *platformContext) Set(p specs.Platform) {
 	c.platform = &p
 }
-
-func (c *platformContext) IsSet() bool {
-	return c.platform != nil
-}

tests/plan.bats

@@ -228,15 +228,17 @@ setup() {
 }
 
 @test "plan/platform" {
+
    cd "$TESTDIR"
 
-   # Run with amd64 platform
-   run "$DAGGER" "do" -p./plan/platform/config_platform_linux_amd64.cue verify
-
-   # Run with arm64 platform
-   run "$DAGGER" "do" -p./plan/platform/config_platform_linux_arm64.cue verify
-
-   # Run with invalid platform
-   run "$DAGGER" "do" -p./plan/platform/config_platform_failure_invalid_platform.cue verify
+   # Run with invalid platform format
+   run "$DAGGER" "do" --experimental-platform invalid -p./plan/platform/platform.cue test
    assert_failure
+   assert_output --partial "unknown operating system or architecture: invalid argument"
+
+
+   # Run with non-existing platform
+   run "$DAGGER" "do" --experimental-platform invalid/invalid -p./plan/platform/platform.cue test
+   assert_failure
+   assert_output --partial "no match for platform in manifest"
 }

tests/plan/platform/config_platform_failure_invalid_platform.cue

@@ -1,33 +0,0 @@
-package main
-
-import (
-	"dagger.io/dagger"
-	"dagger.io/dagger/core"
-)
-
-dagger.#Plan & {
-	platform: "linux/unknown"
-
-	actions: {
-		image: core.#Pull & {
-			source: "alpine:3.15.0"
-		}
-
-		writeArch: core.#Exec & {
-			input:  image.output
-			always: true
-			args: [
-				"sh", "-c", #"""
-					echo -n $(uname -m) >> /arch.txt
-					"""#,
-			]
-		}
-
-		verify: core.#ReadFile & {
-			input: writeArch.output
-			path:  "/arch.txt"
-		} & {
-			contents: "s390x"
-		}
-	}
-}

tests/plan/platform/config_platform_linux_amd64.cue

@@ -1,33 +0,0 @@
-package main
-
-import (
-	"dagger.io/dagger"
-	"dagger.io/dagger/core"
-)
-
-dagger.#Plan & {
-	platform: "linux/amd64"
-
-	actions: {
-		image: core.#Pull & {
-			source: "alpine:3.15.0"
-		}
-
-		writeArch: core.#Exec & {
-			input:  image.output
-			always: true
-			args: [
-				"sh", "-c", #"""
-					echo -n $(uname -m) >> /arch.txt
-					"""#,
-			]
-		}
-
-		verify: core.#ReadFile & {
-			input: writeArch.output
-			path:  "/arch.txt"
-		} & {
-			contents: "x86_64"
-		}
-	}
-}

tests/plan/platform/config_platform_linux_arm64.cue

@@ -1,33 +0,0 @@
-package main
-
-import (
-	"dagger.io/dagger"
-	"dagger.io/dagger/core"
-)
-
-dagger.#Plan & {
-	platform: "linux/arm64"
-
-	actions: {
-		image: core.#Pull & {
-			source: "alpine:3.15.0"
-		}
-
-		writeArch: core.#Exec & {
-			input:  image.output
-			always: true
-			args: [
-				"sh", "-c", #"""
-					echo -n $(uname -m) >> /arch.txt
-					"""#,
-			]
-		}
-
-		verify: core.#ReadFile & {
-			input: writeArch.output
-			path:  "/arch.txt"
-		} & {
-			contents: "aarch64"
-		}
-	}
-}

tests/plan/platform/platform.cue

@@ -0,0 +1,12 @@
+package main
+
+import (
+	"dagger.io/dagger"
+	"dagger.io/dagger/core"
+)
+
+dagger.#Plan & {
+	actions: test: image: core.#Pull & {
+		source: "alpine:3.15.0"
+	}
+}