feat: scan local go mod cache for licenses of golang packages (#1645)

Signed-off-by: Avi Deitcher <avi@deitcher.net>
Co-authored-by: Keith Zantow <kzantow@gmail.com>

syft/source/deferred_resolver.go

@@ -0,0 +1,108 @@
+package source
+
+import (
+	"io"
+
+	"github.com/anchore/syft/internal/log"
+)
+
+func NewDeferredResolverFromSource(creator func() (Source, error)) *DeferredResolver {
+	return NewDeferredResolver(func() (FileResolver, error) {
+		s, err := creator()
+		if err != nil {
+			return nil, err
+		}
+
+		return s.FileResolver(SquashedScope)
+	})
+}
+
+func NewDeferredResolver(creator func() (FileResolver, error)) *DeferredResolver {
+	return &DeferredResolver{
+		creator: creator,
+	}
+}
+
+type DeferredResolver struct {
+	creator  func() (FileResolver, error)
+	resolver FileResolver
+}
+
+func (d *DeferredResolver) getResolver() (FileResolver, error) {
+	if d.resolver == nil {
+		resolver, err := d.creator()
+		if err != nil {
+			return nil, err
+		}
+		d.resolver = resolver
+	}
+	return d.resolver, nil
+}
+
+func (d *DeferredResolver) FileContentsByLocation(location Location) (io.ReadCloser, error) {
+	r, err := d.getResolver()
+	if err != nil {
+		return nil, err
+	}
+	return r.FileContentsByLocation(location)
+}
+
+func (d *DeferredResolver) HasPath(s string) bool {
+	r, err := d.getResolver()
+	if err != nil {
+		log.Debug("unable to get resolver: %v", err)
+		return false
+	}
+	return r.HasPath(s)
+}
+
+func (d *DeferredResolver) FilesByPath(paths ...string) ([]Location, error) {
+	r, err := d.getResolver()
+	if err != nil {
+		return nil, err
+	}
+	return r.FilesByPath(paths...)
+}
+
+func (d *DeferredResolver) FilesByGlob(patterns ...string) ([]Location, error) {
+	r, err := d.getResolver()
+	if err != nil {
+		return nil, err
+	}
+	return r.FilesByGlob(patterns...)
+}
+
+func (d *DeferredResolver) FilesByMIMEType(types ...string) ([]Location, error) {
+	r, err := d.getResolver()
+	if err != nil {
+		return nil, err
+	}
+	return r.FilesByMIMEType(types...)
+}
+
+func (d *DeferredResolver) RelativeFileByPath(location Location, path string) *Location {
+	r, err := d.getResolver()
+	if err != nil {
+		return nil
+	}
+	return r.RelativeFileByPath(location, path)
+}
+
+func (d *DeferredResolver) AllLocations() <-chan Location {
+	r, err := d.getResolver()
+	if err != nil {
+		log.Debug("unable to get resolver: %v", err)
+		return nil
+	}
+	return r.AllLocations()
+}
+
+func (d *DeferredResolver) FileMetadataByLocation(location Location) (FileMetadata, error) {
+	r, err := d.getResolver()
+	if err != nil {
+		return FileMetadata{}, err
+	}
+	return r.FileMetadataByLocation(location)
+}
+
+var _ FileResolver = (*DeferredResolver)(nil)

syft/source/deferred_resolver_test.go

@@ -0,0 +1,24 @@
+package source
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func Test_NewDeferredResolver(t *testing.T) {
+	creatorCalled := false
+
+	deferredResolver := NewDeferredResolver(func() (FileResolver, error) {
+		creatorCalled = true
+		return NewMockResolverForPaths(), nil
+	})
+
+	require.False(t, creatorCalled)
+	require.Nil(t, deferredResolver.resolver)
+
+	_, _ = deferredResolver.FilesByGlob("**/*")
+
+	require.True(t, creatorCalled)
+	require.NotNil(t, deferredResolver.resolver)
+}