internal/encoding/gotypes: support go import aliasing

cmd/cue/cmd/testdata/script/cmd_exp_gengo_alias.txtar

@@ -0,0 +1,46 @@
+# reproduction for https://github.com/cue-lang/cue/issues/3974
+exec cue exp gengotypes
+cmp cue_types_main_gen.go expect-gengo
+
+-- cue.mod/module.cue --
+module: "mod.test"
+language: version: "v0.13.0"
+
+-- pkg/k8s.io/apimachinery/pkg/apis/meta/v1/types_go_gen.cue --
+package v1
+
+#ObjectMeta: {}
+
+-- pkg/k8s.io/api/core/v1/types_go_gen.cue --
+package v1
+
+#PodSpec: {}
+
+-- main.cue --
+package main
+
+import (
+	metav1 "mod.test/pkg/k8s.io/apimachinery/pkg/apis/meta/v1"
+	"mod.test/pkg/k8s.io/api/core/v1"
+)
+
+#Spec: {
+	meta: metav1.#ObjectMeta
+	spec: v1.#PodSpec
+}
+
+-- expect-gengo --
+// Code generated by "cue exp gengotypes"; DO NOT EDIT.
+
+package main
+
+import (
+	"mod.test/pkg/k8s.io/api/core/v1"
+	metav1 "mod.test/pkg/k8s.io/apimachinery/pkg/apis/meta/v1"
+)
+
+type Spec struct {
+	Meta metav1.ObjectMeta `json:"meta"`
+
+	Spec v1.PodSpec `json:"spec"`
+}

cmd/cue/cmd/testdata/script/cmd_exp_gengo_alias_conflict.txtar

@@ -0,0 +1,57 @@
+# reproduction for https://github.com/cue-lang/cue/issues/3974
+exec cue exp gengotypes
+cmp cue_types_main_gen.go expect-gengo
+
+-- cue.mod/module.cue --
+module: "mod.test"
+language: version: "v0.13.0"
+
+-- pkg/foo/p1/p1.cue --
+package p1
+
+#Foo: int
+
+-- pkg/bar/p2/p2.cue --
+package p2
+
+#Bar: string
+
+-- f1.cue --
+package main
+
+import (
+	same "mod.test/pkg/foo/p1"
+)
+
+#A: {
+	foo: same.#Foo
+}
+
+-- f2.cue --
+package main
+
+import (
+	same "mod.test/pkg/bar/p2"
+)
+
+#B: {
+	bar: same.#Bar
+}
+
+-- expect-gengo --
+// Code generated by "cue exp gengotypes"; DO NOT EDIT.
+
+package main
+
+import (
+	same1 "mod.test/pkg/bar/p2"
+	same "mod.test/pkg/foo/p1"
+)
+
+type A struct {
+	Foo same.Foo `json:"foo"`
+}
+
+type B struct {
+	Bar same1.Bar `json:"bar"`
+}

cmd/cue/cmd/testdata/script/cmd_exp_gengo_alias_duplicate.txtar

@@ -0,0 +1,57 @@
+# reproduction for https://github.com/cue-lang/cue/issues/3974
+exec cue exp gengotypes
+cmp cue_types_main_gen.go expect-gengo
+
+-- cue.mod/module.cue --
+module: "mod.test"
+language: version: "v0.13.0"
+
+-- pkg/same/same.cue --
+package same
+
+#Same: int
+
+-- pkg/foo/foo.cue --
+package foo
+
+#Bar: string
+
+-- f1.cue --
+package main
+
+import (
+	"mod.test/pkg/same"
+)
+
+#A: {
+	value: same.#Same
+}
+
+-- f2.cue --
+package main
+
+import (
+	same "mod.test/pkg/foo"
+)
+
+#B: {
+	bar: same.#Bar
+}
+
+-- expect-gengo --
+// Code generated by "cue exp gengotypes"; DO NOT EDIT.
+
+package main
+
+import (
+	same1 "mod.test/pkg/foo"
+	"mod.test/pkg/same"
+)
+
+type A struct {
+	Value same.Same `json:"value"`
+}
+
+type B struct {
+	Bar same1.Bar `json:"bar"`
+}

internal/encoding/gotypes/generate.go

@@ -70,6 +70,15 @@ func Generate(ctx *cue.Context, insts ...*build.Instance) error {
 		g.pkgRoot = instVal
 		g.importCuePkgAsGoPkg = make(map[string]string)
 
+		// gather the import aliases for the instance.
+		// NOTE: this implementation means that if an import alias is employed in one file
+		// it will be used anywhere that package is referenced
+		importAliases, err := gatherImportAliases(inst)
+		if err != nil {
+			return err
+		}
+		g.importAliases = importAliases
+
 		iter, err := instVal.Fields(cue.Definitions(true))
 		if err != nil {
 			return err
@@ -100,7 +109,7 @@ func Generate(ctx *cue.Context, insts ...*build.Instance) error {
 			buf = fmt.Appendf(buf, format, args...)
 		}
 		printf("// Code generated by \"cue exp gengotypes\"; DO NOT EDIT.\n\n")
-		goPkgName := goPkgNameForInstance(inst, instVal)
+		goPkgName := goPkgNameForInstance(inst, instVal, nil)
 		if prev, ok := goPkgNamesDoneByDir[inst.Dir]; ok && prev != goPkgName {
 			return fmt.Errorf("cannot generate two Go packages in one directory; %s and %s", prev, goPkgName)
 		} else {
@@ -112,7 +121,11 @@ func Generate(ctx *cue.Context, insts ...*build.Instance) error {
 		if len(importedGo) > 0 {
 			printf("import (\n")
 			for _, path := range importedGo {
-				printf("\t%q\n", path)
+				if alias, ok := g.importAliases[path]; ok {
+					printf("\t%s %q\n", alias, path)
+				} else {
+					printf("\t%q\n", path)
+				}
 			}
 			printf(")\n")
 		}
@@ -217,6 +230,11 @@ type generator struct {
 
 	// def tracks the generation state for a single CUE definition.
 	def *generatedDef
+
+	// importAliases maps package names to a given alias. In the case that there are multiple aliases present for
+	// same package then we will use the first alias encountered. When the same alias is used for multiple packages
+	// across different files, then a number will be added to the end of the alias to avoid conflicts.
+	importAliases map[string]string
 }
 
 type qualifiedPath = string // [build.Instance.ImportPath] + " " + [cue.Path.String]
@@ -679,11 +697,16 @@ func goValueAttr(val cue.Value) cue.Attribute {
 
 // goPkgNameForInstance determines what to name a Go package generated from a CUE instance.
 // By default this is the CUE package name, but it can be overriden by a @go() package attribute.
-func goPkgNameForInstance(inst *build.Instance, instVal cue.Value) string {
+// When supplying importAliases, and if no package attribute is found, the returned package name
+// reflects the alias name that the package is being imported as.
+func goPkgNameForInstance(inst *build.Instance, instVal cue.Value, importAliases map[string]string) string {
 	attr := goValueAttr(instVal)
 	if s, _ := attr.String(0); s != "" {
 		return s
 	}
+	if alias, ok := importAliases[inst.ImportPath]; ok {
+		return alias
+	}
 	return inst.PkgName
 }
 
@@ -751,7 +774,7 @@ func (g *generator) emitTypeReference(val cue.Value) (bool, typeFacts, error) {
 		facts.isNillable = true // pointers can be nil
 	}
 	if root != g.pkgRoot {
-		g.def.printf("%s.", goPkgNameForInstance(inst, root))
+		g.def.printf("%s.", goPkgNameForInstance(inst, root, g.importAliases))
 	}
 	g.def.printf("%s", name)
 	return true, facts, nil
@@ -772,3 +795,45 @@ func emitDocs(printf func(string, ...any), name string, groups []*ast.CommentGro
 		}
 	}
 }
+
+// gatherImportAliases collects the aliases from imports across the instance.
+func gatherImportAliases(inst *build.Instance) (map[string]string, error) {
+	fileAliases := make(map[string]string)
+	tracked := make(map[string]int)
+
+	type pair struct{ path, alias string }
+	var explicit []pair
+
+	for _, f := range inst.Files {
+		for _, s := range f.Imports {
+			if s.Path == nil {
+				continue
+			}
+			pkgPath, err := strconv.Unquote(s.Path.Value)
+			if err != nil {
+				return nil, err
+			}
+			// Unaliased import: reserve its base name
+			if s.Name == nil {
+				base := filepath.Base(pkgPath)
+				tracked[base]++
+				continue
+			}
+			// Explicit alias: queue for resolution
+			alias := s.Name.Name
+			explicit = append(explicit, pair{path: pkgPath, alias: alias})
+		}
+	}
+
+	// Resolve explicit aliases with conflict suffixing.
+	for _, e := range explicit {
+		alias := e.alias
+		if count, ok := tracked[alias]; ok {
+			alias = fmt.Sprintf("%s%d", alias, count)
+		}
+		fileAliases[e.path] = alias
+		tracked[e.alias]++ // track the alias name (unsuffixed) for future conflicts
+	}
+
+	return fileAliases, nil
+}