bake: fix file-relative target references

Signed-off-by: CrazyMax <1951866+crazy-max@users.noreply.github.com>

bake/bake.go

@@ -437,7 +437,22 @@ func fileRelativePaths(opts []ParseOpt) bool {
 }
 
 func rebaseContextPaths(c *Config) {
+	targets := make(map[string]*Target, len(c.Targets))
 	for _, t := range c.Targets {
+		targets[t.Name] = t
+	}
+
+	for _, t := range c.Targets {
+		if ref := targets[t.contextBaseRef]; ref != nil {
+			switch {
+			case ref.hasContextBase:
+				t.contextBase = ref.contextBase
+				t.hasContextBase = true
+			case ref.hasDefaultContextBase:
+				t.contextBase = ref.defaultContextBase
+				t.hasContextBase = true
+			}
+		}
 		t.rebaseContextPaths()
 	}
 }
@@ -854,6 +869,7 @@ type Target struct {
 	useDefaultContextBase bool
 	contextBase           string
 	hasContextBase        bool
+	contextBaseRef        string
 	contextsBase          map[string]string
 }
 
@@ -922,9 +938,10 @@ func (t *Target) SetBlockSource(block *hcl.Block) {
 	if diags.HasErrors() {
 		return
 	}
-	if _, ok := content.Attributes["context"]; ok {
+	if attr, ok := content.Attributes["context"]; ok {
 		t.contextBase = base
 		t.hasContextBase = true
+		t.contextBaseRef = targetContextRef(attr.Expr)
 	}
 	if _, ok := content.Attributes["contexts"]; ok {
 		t.setContextsBase(base)
@@ -943,6 +960,41 @@ func (t *Target) setContextsBase(base string) {
 	}
 }
 
+func targetContextRef(expr hcl.Expression) string {
+	traversal, diags := hcl.AbsTraversalForExpr(expr)
+	if diags.HasErrors() || len(traversal) != 3 {
+		return ""
+	}
+	root, ok := traversal[0].(hcl.TraverseRoot)
+	if !ok || root.Name != "target" {
+		return ""
+	}
+	target, ok := traversalStepName(traversal[1])
+	if !ok {
+		return ""
+	}
+	field, ok := traversal[2].(hcl.TraverseAttr)
+	if !ok || field.Name != "context" {
+		return ""
+	}
+	return target
+}
+
+func traversalStepName(step hcl.Traverser) (string, bool) {
+	switch step := step.(type) {
+	case hcl.TraverseAttr:
+		return step.Name, true
+	case hcl.TraverseIndex:
+		key, err := convert.Convert(step.Key, cty.String)
+		if err != nil || key.IsNull() || !key.IsKnown() {
+			return "", false
+		}
+		return key.AsString(), true
+	default:
+		return "", false
+	}
+}
+
 func (t *Target) normalize() {
 	t.Annotations = removeDupesStr(t.Annotations)
 	t.Attest = t.Attest.Normalize()
@@ -982,6 +1034,7 @@ func (t *Target) Merge(t2 *Target) {
 		t.Context = t2.Context
 		t.contextBase = t2.contextBase
 		t.hasContextBase = t2.hasContextBase
+		t.contextBaseRef = t2.contextBaseRef
 	}
 	if t2.Dockerfile != nil {
 		t.Dockerfile = t2.Dockerfile

bake/bake_test.go

@@ -918,6 +918,30 @@ target "app" {
 	})
 }
 
+func TestTargetReferenceContextRebase(t *testing.T) {
+	fp1 := File{
+		Name: filepath.Join("one", "docker-bake.hcl"),
+		Data: []byte(`
+target "base" {
+  context = "basectx"
+}`),
+	}
+	fp2 := File{
+		Name: filepath.Join("two", "docker-bake.hcl"),
+		Data: []byte(`
+target "app" {
+  context = target.base.context
+}`),
+	}
+
+	m, _, err := ReadTargets(context.TODO(), []File{fp1, fp2}, []string{"app"}, nil, nil, nil, &EntitlementConf{}, ParseOpt{
+		FileRelativePaths: true,
+	})
+	require.NoError(t, err)
+
+	require.Equal(t, filepath.ToSlash(filepath.Clean("one/basectx")), *m["app"].Context)
+}
+
 func TestOverridesNotRebased(t *testing.T) {
 	fp := File{
 		Name: filepath.Join("subdir", "docker-bake.hcl"),

tests/bake.go

@@ -786,6 +786,48 @@ EOT
 		require.FileExists(t, filepath.Join(dirDest, "marker"))
 	})
 
+	t.Run("hcl target reference", func(t *testing.T) {
+		baseBakefile := []byte(`
+target "base" {
+  context = "basectx"
+}
+`)
+		appBakefile := []byte(`
+target "app" {
+  context = target.base.context
+  dockerfile-inline = <<EOT
+FROM scratch
+COPY marker /marker
+EOT
+}
+`)
+
+		dir := tmpdir(
+			t,
+			fstest.CreateDir("one", 0700),
+			fstest.CreateDir("one/basectx", 0700),
+			fstest.CreateDir("two", 0700),
+			fstest.CreateDir("two/basectx", 0700),
+			fstest.CreateFile("one/docker-bake.hcl", baseBakefile, 0600),
+			fstest.CreateFile("one/basectx/marker", []byte("source-file"), 0600),
+			fstest.CreateFile("two/docker-bake.hcl", appBakefile, 0600),
+			fstest.CreateFile("two/basectx/marker", []byte("consumer-file"), 0600),
+		)
+		dirDest := t.TempDir()
+
+		out, err := bakeCmd(
+			sb,
+			withDir(dir),
+			withArgs("--file", "one/docker-bake.hcl", "--file", "two/docker-bake.hcl", "--set", "app.output=type=local,dest="+dirDest, "app"),
+			withEnv("BUILDX_BAKE_FILE_RELATIVE_PATHS=1"),
+		)
+		require.NoError(t, err, out)
+
+		dt, err := os.ReadFile(filepath.Join(dirDest, "marker"))
+		require.NoError(t, err)
+		require.Equal(t, "source-file", string(dt))
+	})
+
 	t.Run("cwd prefix", func(t *testing.T) {
 		bakefile := []byte(`
 target "default" {