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Add support for generic type aliases (#211)
1 parent 69014e2 commit c7d2360

5 files changed

Lines changed: 210 additions & 17 deletions

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‎internal/document/document.go‎

Lines changed: 28 additions & 17 deletions
Original file line numberDiff line numberDiff line change
@@ -226,28 +226,18 @@ func formatTypeDeclaration(obj *types.TypeName) string {
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return fmt.Sprintf("type %s %s", obj.Name(), expandTypeExpr(obj.Pkg(), obj.Type().Underlying()))
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}
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// qualifiedName returns the name of original, prefixed with its package name
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// if it differs from obj's package. Handles nil packages (builtins).
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func qualifiedName(obj, original types.Object) string {
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objPkg := obj.Pkg()
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origPkg := original.Pkg()
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if objPkg == nil || origPkg == nil || objPkg.Name() == origPkg.Name() {
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return original.Name()
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}
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return origPkg.Name() + "." + original.Name()
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}
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// formatAliasDeclaration returns the type declaration for alias types.
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func formatAliasDeclaration(obj *types.TypeName) string {
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switch ty := obj.Type().(type) {
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case *types.Alias:
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switch rhs := ty.Rhs().(type) {
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case *types.Alias:
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return fmt.Sprintf("type %s = %s", obj.Name(), qualifiedName(obj, rhs.Obj()))
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case *types.Named:
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return fmt.Sprintf("type %s = %s", obj.Name(), qualifiedName(obj, rhs.Obj()))
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qual := relativeQualifier(obj.Pkg())
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lhs := obj.Name() + formatTypeParamList(ty.TypeParams())
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rhs := ty.Rhs()
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switch rhs.(type) {
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case *types.Alias, *types.Named:
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return fmt.Sprintf("type %s = %s", lhs, types.TypeString(rhs, qual))
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default:
250-
return fmt.Sprintf("type %s = %s", obj.Name(), expandTypeExpr(obj.Pkg(), rhs))
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return fmt.Sprintf("type %s = %s", lhs, expandTypeExpr(obj.Pkg(), rhs))
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}
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default:
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if val := os.Getenv("GODEBUG"); strings.Contains(val, "gotypealias=0") {
@@ -266,6 +256,27 @@ func formatAliasDeclaration(obj *types.TypeName) string {
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return fmt.Sprintf("type %s %s", obj.Name(), expandTypeExpr(obj.Pkg(), obj.Type().Underlying()))
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}
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// formatTypeParamList renders a TypeParamList as "[K C1, V C2]".
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// Returns "" when tparams is nil or empty.
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func formatTypeParamList(tparams *types.TypeParamList) string {
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if tparams == nil || tparams.Len() == 0 {
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return ""
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}
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var buf strings.Builder
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buf.WriteByte('[')
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for i := range tparams.Len() {
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if i > 0 {
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buf.WriteString(", ")
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}
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tp := tparams.At(i)
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buf.WriteString(tp.Obj().Name())
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buf.WriteByte(' ')
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buf.WriteString(tp.Constraint().String())
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}
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buf.WriteByte(']')
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return buf.String()
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}
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269280
// expandTypeExpr renders a type expression, formatting struct and interface
270281
// types with aligned fields using go/format.
271282
func expandTypeExpr(pkg *types.Package, t types.Type) string {

‎internal/testdata/snapshots/input/pr211/README.md‎

Lines changed: 20 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,20 @@
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# pr211 --- Generic type aliases
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This test covers generic type alias support, addressing [#112].
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Go 1.24 introduced generic type aliases ([go#46477]), allowing type aliases to
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carry their own type parameters:
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```go
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type Set[K comparable] = Map[K, bool]
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```
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The indexer must correctly:
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- Emit definitions for the alias and its type parameters.
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- Emit references from the alias's RHS to the aliased type and its type
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arguments.
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- Render hover documentation that includes the type parameter list.
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[#112]: https://github.com/sourcegraph/scip-go/issues/112
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[go#46477]: https://github.com/golang/go/issues/46477

‎internal/testdata/snapshots/input/pr211/generic_alias.go‎

Lines changed: 30 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,30 @@
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package pr211
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// Map is a generic map type.
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type Map[K comparable, V any] struct {
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entries []entry[K, V]
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}
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type entry[K comparable, V any] struct {
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key K
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value V
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}
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// Set is a generic alias that partially instantiates Map.
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type Set[K comparable] = Map[K, bool]
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// Alias with a tighter constraint.
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type OrderedSet[K ~int | ~string] = Set[K]
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// Alias of an alias (chained).
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type StringSet = Set[string]
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// Alias with all params forwarded.
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type PairMap[K comparable, V any] = Map[K, V]
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func UseAliases() {
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_ = Set[int]{}
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_ = OrderedSet[int]{}
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_ = StringSet{}
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_ = PairMap[string, int]{}
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}

‎internal/testdata/snapshots/input/pr211/go.mod‎

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,3 @@
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module sg/pr211
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go 1.24

‎internal/testdata/snapshots/output/pr211/generic_alias.go‎

Lines changed: 129 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,129 @@
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package pr211
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// ^^^^^ definition 0.1.test `sg/pr211`/
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// display_name pr211
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// signature_documentation
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// > package pr211
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// Map is a generic map type.
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type Map[K comparable, V any] struct {
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// ^^^ definition 0.1.test `sg/pr211`/Map#
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// signature_documentation
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// > type Map struct{ entries []entry[K, V] }
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// documentation
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// > Map is a generic map type.
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// ^ definition local 0
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// display_name K
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// signature_documentation
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// > type parameter K comparable
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// ^ definition local 1
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// display_name V
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// signature_documentation
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// > type parameter V any
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entries []entry[K, V]
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// ^^^^^^^ definition 0.1.test `sg/pr211`/Map#entries.
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// signature_documentation
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// > struct field entries []entry[K, V]
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// ^^^^^ reference 0.1.test `sg/pr211`/entry#
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// ^ reference local 0
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// ^ reference local 1
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}
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type entry[K comparable, V any] struct {
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// ^^^^^ definition 0.1.test `sg/pr211`/entry#
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// signature_documentation
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// > type entry struct {
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// > key K
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// > value V
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// > }
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// ^ definition local 2
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// display_name K
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// signature_documentation
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// > type parameter K comparable
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// ^ definition local 3
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// display_name V
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// signature_documentation
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// > type parameter V any
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key K
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// ^^^ definition 0.1.test `sg/pr211`/entry#key.
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// signature_documentation
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// > struct field key K
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// ^ reference local 2
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value V
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// ^^^^^ definition 0.1.test `sg/pr211`/entry#value.
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// signature_documentation
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// > struct field value V
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// ^ reference local 3
56+
}
57+
58+
// Set is a generic alias that partially instantiates Map.
59+
type Set[K comparable] = Map[K, bool]
60+
// ^^^ definition 0.1.test `sg/pr211`/Set#
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// signature_documentation
62+
// > type Set[K comparable] = Map[K, bool]
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// documentation
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// > Set is a generic alias that partially instantiates Map.
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// ^ definition local 4
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// display_name K
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// signature_documentation
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// > type parameter K comparable
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// ^^^ reference 0.1.test `sg/pr211`/Map#
70+
// ^ reference local 4
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72+
// Alias with a tighter constraint.
73+
type OrderedSet[K ~int | ~string] = Set[K]
74+
// ^^^^^^^^^^ definition 0.1.test `sg/pr211`/OrderedSet#
75+
// signature_documentation
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// > type OrderedSet[K ~int | ~string] = Set[K]
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// documentation
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// > Alias with a tighter constraint.
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// ^ definition local 5
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// display_name K
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// signature_documentation
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// > type parameter K ~int | ~string
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// ^^^ reference 0.1.test `sg/pr211`/Set#
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// ^ reference local 5
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86+
// Alias of an alias (chained).
87+
type StringSet = Set[string]
88+
// ^^^^^^^^^ definition 0.1.test `sg/pr211`/StringSet#
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// signature_documentation
90+
// > type StringSet = Set[string]
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// documentation
92+
// > Alias of an alias (chained).
93+
// ^^^ reference 0.1.test `sg/pr211`/Set#
94+
95+
// Alias with all params forwarded.
96+
type PairMap[K comparable, V any] = Map[K, V]
97+
// ^^^^^^^ definition 0.1.test `sg/pr211`/PairMap#
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// signature_documentation
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// > type PairMap[K comparable, V any] = Map[K, V]
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// documentation
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// > Alias with all params forwarded.
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// ^ definition local 6
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// display_name K
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// signature_documentation
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// > type parameter K comparable
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// ^ definition local 7
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// display_name V
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// signature_documentation
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// > type parameter V any
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// ^^^ reference 0.1.test `sg/pr211`/Map#
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// ^ reference local 6
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// ^ reference local 7
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114+
//⌄ enclosing_range_start 0.1.test `sg/pr211`/UseAliases().
115+
func UseAliases() {
116+
// ^^^^^^^^^^ definition 0.1.test `sg/pr211`/UseAliases().
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// signature_documentation
118+
// > func UseAliases()
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_ = Set[int]{}
120+
// ^^^ reference 0.1.test `sg/pr211`/Set#
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_ = OrderedSet[int]{}
122+
// ^^^^^^^^^^ reference 0.1.test `sg/pr211`/OrderedSet#
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_ = StringSet{}
124+
// ^^^^^^^^^ reference 0.1.test `sg/pr211`/StringSet#
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_ = PairMap[string, int]{}
126+
// ^^^^^^^ reference 0.1.test `sg/pr211`/PairMap#
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}
128+
//⌃ enclosing_range_end 0.1.test `sg/pr211`/UseAliases().
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