build: take advantage of --platform lists

The builder can take a list of platforms in the Platforms field of its
BuildOptions argument, and we should definitely take advantage of that.

The `bud-multiple-platform-values` test from buildah exercises support
for this, so
[NO TESTS NEEDED]

Signed-off-by: Nalin Dahyabhai <nalin@redhat.com>

cmd/podman/images/build.go

@@ -476,7 +476,7 @@ func buildFlagsWrapperToOptions(c *cobra.Command, contextDir string, flags *buil
 		runtimeFlags = append(runtimeFlags, "--systemd-cgroup")
 	}
 
-	imageOS, arch, err := parse.PlatformFromOptions(c)
+	platforms, err := parse.PlatformsFromOptions(c)
 	if err != nil {
 		return nil, err
 	}
@@ -490,7 +490,6 @@ func buildFlagsWrapperToOptions(c *cobra.Command, contextDir string, flags *buil
 		AddCapabilities:         flags.CapAdd,
 		AdditionalTags:          tags,
 		Annotations:             flags.Annotation,
-		Architecture:            arch,
 		Args:                    args,
 		BlobDirectory:           flags.BlobCache,
 		CNIConfigDir:            flags.CNIConfigDir,
@@ -516,11 +515,11 @@ func buildFlagsWrapperToOptions(c *cobra.Command, contextDir string, flags *buil
 		MaxPullPushRetries:      3,
 		NamespaceOptions:        nsValues,
 		NoCache:                 flags.NoCache,
-		OS:                      imageOS,
 		OciDecryptConfig:        decConfig,
 		Out:                     stdout,
 		Output:                  output,
 		OutputFormat:            format,
+		Platforms:               platforms,
 		PullPolicy:              pullPolicy,
 		PullPushRetryDelay:      2 * time.Second,
 		Quiet:                   flags.Quiet,

pkg/api/handlers/compat/images_build.go

@@ -106,7 +106,7 @@ func BuildImage(w http.ResponseWriter, r *http.Request) {
 		NamespaceOptions       string   `schema:"nsoptions"`
 		NoCache                bool     `schema:"nocache"`
 		OutputFormat           string   `schema:"outputformat"`
-		Platform               string   `schema:"platform"`
+		Platform               []string `schema:"platform"`
 		Pull                   bool     `schema:"pull"`
 		PullPolicy             string   `schema:"pullpolicy"`
 		Quiet                  bool     `schema:"q"`
@@ -126,7 +126,6 @@ func BuildImage(w http.ResponseWriter, r *http.Request) {
 		Registry:   "docker.io",
 		Rm:         true,
 		ShmSize:    64 * 1024 * 1024,
-		Tag:        []string{},
 	}
 
 	decoder := r.Context().Value(api.DecoderKey).(*schema.Decoder)
@@ -481,16 +480,17 @@ func BuildImage(w http.ResponseWriter, r *http.Request) {
 		},
 	}
 
-	if len(query.Platform) > 0 {
-		variant := ""
-		buildOptions.OS, buildOptions.Architecture, variant, err = parse.Platform(query.Platform)
+	for _, platformSpec := range query.Platform {
+		os, arch, variant, err := parse.Platform(platformSpec)
 		if err != nil {
-			utils.BadRequest(w, "platform", query.Platform, err)
+			utils.BadRequest(w, "platform", platformSpec, err)
 			return
 		}
-		buildOptions.SystemContext.OSChoice = buildOptions.OS
-		buildOptions.SystemContext.ArchitectureChoice = buildOptions.Architecture
-		buildOptions.SystemContext.VariantChoice = variant
+		buildOptions.Platforms = append(buildOptions.Platforms, struct{ OS, Arch, Variant string }{
+			OS:      os,
+			Arch:    arch,
+			Variant: variant,
+		})
 	}
 	if _, found := r.URL.Query()["timestamp"]; found {
 		ts := time.Unix(query.Timestamp, 0)

pkg/bindings/images/build.go

@@ -220,6 +220,16 @@ func Build(ctx context.Context, containerFiles []string, options entities.BuildO
 	if len(platform) > 0 {
 		params.Set("platform", platform)
 	}
+	if len(options.Platforms) > 0 {
+		params.Del("platform")
+		for _, platformSpec := range options.Platforms {
+			platform = platformSpec.OS + "/" + platformSpec.Arch
+			if platformSpec.Variant != "" {
+				platform += "/" + platformSpec.Variant
+			}
+			params.Add("platform", platform)
+		}
+	}
 
 	params.Set("pullpolicy", options.PullPolicy.String())