Builder: Check remote when local img platform doesn't match

This fixes an issue where if a build requests an image that already
exists in Docker's image store but does not match the specified build
platform, instead of building using the wrong platform go ahead and
check the remote for the correct platform.

Steps to reproduce issue:

```terminal
$ docker pull --platform=amd64 debian:buster
<output supressed>
$ cat Dockerfile
FROM debian:buster
RUN echo hello
$ docker build --platform=armhf -< Dockerfile
<output supressed>
```

Without this fix, the build invokcation will build using the amd64 image
since it is already tagged locally, but this is clearly not what we
want.

With the fix the local image is not used and instead we pull the correct
image.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

builder/builder-next/adapters/containerimage/pull.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"io"
 	"io/ioutil"
+	"path"
 	"runtime"
 	"sync"
 	"sync/atomic"
@@ -41,6 +42,7 @@ import (
 	"github.com/opencontainers/image-spec/identity"
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
 	"github.com/pkg/errors"
+	"github.com/sirupsen/logrus"
 	"golang.org/x/time/rate"
 )
 
@@ -114,7 +116,7 @@ func (is *imageSource) getCredentialsFromSession(ctx context.Context, sm *sessio
 	}
 }
 
-func (is *imageSource) resolveLocal(refStr string) ([]byte, error) {
+func (is *imageSource) resolveLocal(refStr string) (*image.Image, error) {
 	ref, err := distreference.ParseNormalizedNamed(refStr)
 	if err != nil {
 		return nil, err
@@ -127,7 +129,7 @@ func (is *imageSource) resolveLocal(refStr string) ([]byte, error) {
 	if err != nil {
 		return nil, err
 	}
-	return img.RawJSON(), nil
+	return img, nil
 }
 
 func (is *imageSource) resolveRemote(ctx context.Context, ref string, platform *ocispec.Platform, sm *session.Manager) (digest.Digest, []byte, error) {
@@ -174,9 +176,16 @@ func (is *imageSource) ResolveImageConfig(ctx context.Context, ref string, opt l
 		// default == prefer local, but in the future could be smarter
 		fallthrough
 	case source.ResolveModePreferLocal:
-		dt, err := is.resolveLocal(ref)
+		img, err := is.resolveLocal(ref)
 		if err == nil {
-			return "", dt, err
+			if img.Architecture != opt.Platform.Architecture || img.Variant != opt.Platform.Variant || img.OS != opt.Platform.OS {
+				logrus.WithField("ref", ref).Debugf("Requested build platform %s does not match local image platform %s, checking remote",
+					path.Join(opt.Platform.OS, opt.Platform.Architecture, opt.Platform.Variant),
+					path.Join(img.OS, img.Architecture, img.Variant),
+				)
+			} else {
+				return "", img.RawJSON(), err
+			}
 		}
 		// fallback to remote
 		return is.resolveRemote(ctx, ref, opt.Platform, sm)
@@ -261,9 +270,17 @@ func (p *puller) resolveLocal() {
 		}
 
 		if p.src.ResolveMode == source.ResolveModeDefault || p.src.ResolveMode == source.ResolveModePreferLocal {
-			dt, err := p.is.resolveLocal(p.src.Reference.String())
+			ref := p.src.Reference.String()
+			img, err := p.is.resolveLocal(ref)
 			if err == nil {
-				p.config = dt
+				if img.Architecture != p.platform.Architecture || img.Variant != p.platform.Variant || img.OS != p.platform.OS {
+					logrus.WithField("ref", ref).Debugf("Requested build platform %s does not match local image platform %s, not resolving",
+						path.Join(p.platform.OS, p.platform.Architecture, p.platform.Variant),
+						path.Join(img.OS, img.Architecture, img.Variant),
+					)
+				} else {
+					p.config = img.RawJSON()
+				}
 			}
 		}
 	})