Handle context cancellation during builds (#539)

`buildx.Build` doesn't terminate if context is canceled, so this PR
rearranges things such that we can wait for the build or context to
finish.

Fixes #533.

provider/internal/mockclient_test.go

@@ -3,7 +3,7 @@
 //
 // Generated by this command:
 //
-//	mockgen -typed -package internal -source client.go -destination mockclient_test.go --self_package github.com/pulumi/pulumi-docker-build/provider/internal
+//	mockgen -typed -package internal -source client.go -destination mockclient_test.go --self_package github.com/pulumi/pulumi-docker-build/provider/internal -imports buildx=github.com/docker/buildx/build
 //
 
 // Package internal is a generated GoMock package.
@@ -13,7 +13,12 @@ import (
 	context "context"
 	reflect "reflect"
 
+	buildx "github.com/docker/buildx/build"
+	builder "github.com/docker/buildx/builder"
 	pb "github.com/docker/buildx/controller/pb"
+	confutil "github.com/docker/buildx/util/confutil"
+	dockerutil "github.com/docker/buildx/util/dockerutil"
+	progress "github.com/docker/buildx/util/progress"
 	client "github.com/moby/buildkit/client"
 	session "github.com/moby/buildkit/session"
 	descriptor "github.com/regclient/regclient/types/descriptor"
@@ -532,3 +537,66 @@ func (c *MockBuildShouldExecCall) DoAndReturn(f func() bool) *MockBuildShouldExe
 	c.Call = c.Call.DoAndReturn(f)
 	return c
 }
+
+// MockBuilder is a mock of Builder interface.
+type MockBuilder struct {
+	ctrl     *gomock.Controller
+	recorder *MockBuilderMockRecorder
+	isgomock struct{}
+}
+
+// MockBuilderMockRecorder is the mock recorder for MockBuilder.
+type MockBuilderMockRecorder struct {
+	mock *MockBuilder
+}
+
+// NewMockBuilder creates a new mock instance.
+func NewMockBuilder(ctrl *gomock.Controller) *MockBuilder {
+	mock := &MockBuilder{ctrl: ctrl}
+	mock.recorder = &MockBuilderMockRecorder{mock}
+	return mock
+}
+
+// EXPECT returns an object that allows the caller to indicate expected use.
+func (m *MockBuilder) EXPECT() *MockBuilderMockRecorder {
+	return m.recorder
+}
+
+// Build mocks base method.
+func (m *MockBuilder) Build(ctx context.Context, nodes []builder.Node, opts map[string]buildx.Options, docker *dockerutil.Client, cfg *confutil.Config, w progress.Writer) (map[string]*client.SolveResponse, error) {
+	m.ctrl.T.Helper()
+	ret := m.ctrl.Call(m, "Build", ctx, nodes, opts, docker, cfg, w)
+	ret0, _ := ret[0].(map[string]*client.SolveResponse)
+	ret1, _ := ret[1].(error)
+	return ret0, ret1
+}
+
+// Build indicates an expected call of Build.
+func (mr *MockBuilderMockRecorder) Build(ctx, nodes, opts, docker, cfg, w any) *MockBuilderBuildCall {
+	mr.mock.ctrl.T.Helper()
+	call := mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Build", reflect.TypeOf((*MockBuilder)(nil).Build), ctx, nodes, opts, docker, cfg, w)
+	return &MockBuilderBuildCall{Call: call}
+}
+
+// MockBuilderBuildCall wrap *gomock.Call
+type MockBuilderBuildCall struct {
+	*gomock.Call
+}
+
+// Return rewrite *gomock.Call.Return
+func (c *MockBuilderBuildCall) Return(resp map[string]*client.SolveResponse, err error) *MockBuilderBuildCall {
+	c.Call = c.Call.Return(resp, err)
+	return c
+}
+
+// Do rewrite *gomock.Call.Do
+func (c *MockBuilderBuildCall) Do(f func(context.Context, []builder.Node, map[string]buildx.Options, *dockerutil.Client, *confutil.Config, progress.Writer) (map[string]*client.SolveResponse, error)) *MockBuilderBuildCall {
+	c.Call = c.Call.Do(f)
+	return c
+}
+
+// DoAndReturn rewrite *gomock.Call.DoAndReturn
+func (c *MockBuilderBuildCall) DoAndReturn(f func(context.Context, []builder.Node, map[string]buildx.Options, *dockerutil.Client, *confutil.Config, progress.Writer) (map[string]*client.SolveResponse, error)) *MockBuilderBuildCall {
+	c.Call = c.Call.DoAndReturn(f)
+	return c
+}