From a9c0aeaa59021f3de35a90393fa8c98362ba1768 Mon Sep 17 00:00:00 2001
From: Carlos Cobo <carlos@remotely.works>
Date: Tue, 29 Jul 2025 13:29:26 +0200
Subject: [PATCH 1/2] feat: avoid generating repeated type constraints

---
 bindings/declarations.go | 43 ++++++++++++++++++++++++++--------------
 testdata/union/union.go  |  1 -
 testdata/union/union.ts  |  2 +-
 3 files changed, 29 insertions(+), 17 deletions(-)

diff --git a/bindings/declarations.go b/bindings/declarations.go
index 19dacc1..7b866e9 100644
--- a/bindings/declarations.go
+++ b/bindings/declarations.go
@@ -1,10 +1,5 @@
 package bindings
 
-import (
-	"fmt"
-	"reflect"
-)
-
 // DeclarationType is any type that can exist at the top level of a AST.
 // Meaning it can be serialized into valid Typescript.
 type DeclarationType interface {
@@ -69,23 +64,41 @@ func (p *TypeParameter) isNode() {}
 
 // Simplify removes duplicate type parameters
 func Simplify(p []*TypeParameter) ([]*TypeParameter, error) {
-	params := make([]*TypeParameter, 0, len(p))
-	exists := make(map[string]*TypeParameter)
+	params := []*TypeParameter{}
+	set := make(map[string]bool)
 	for _, tp := range p {
-		if found, ok := exists[tp.Name.Ref()]; ok {
-			// Compare types, make sure they are the same
-			equal := reflect.DeepEqual(found, tp)
-			if !equal {
-				return nil, fmt.Errorf("type parameter %q already exists with different type", tp.Name)
+		ref := tp.Name.Ref()
+		if _, ok := set[ref]; !ok {
+			params = append(params, tp)
+			set[ref] = true
+
+			if union, ok := tp.Type.(*UnionType); ok {
+				simplifyUnion(union)
 			}
-			continue
 		}
-		params = append(params, tp)
-		exists[tp.Name.Ref()] = tp
 	}
 	return params, nil
 }
 
+func simplifyUnion(union *UnionType) *UnionType {
+	types := []ExpressionType{}
+	set := map[string]bool{}
+	for _, arg := range union.Types {
+		switch v := arg.(type) {
+		case *LiteralKeyword:
+			key := v.String()
+			if _, ok := set[key]; !ok {
+				set[key] = true
+				types = append(types, arg)
+			}
+		default:
+			types = append(types, arg)
+		}
+	}
+	union.Types = types
+	return union
+}
+
 // VariableStatement is a top level declaration of a variable
 // var foo: string = "bar"
 // const foo: string = "bar"
diff --git a/testdata/union/union.go b/testdata/union/union.go
index bd228f3..9171f14 100644
--- a/testdata/union/union.go
+++ b/testdata/union/union.go
@@ -5,7 +5,6 @@ type UnionConstraint[T string | int64] struct {
 }
 
 // Repeated constraints are redundant
-// TODO: Write a mutation to remove redundant constraints
 type Repeated[T string | string | int64 | uint64] struct {
 	Value T
 }
diff --git a/testdata/union/union.ts b/testdata/union/union.ts
index e0282cc..15f2eb1 100644
--- a/testdata/union/union.ts
+++ b/testdata/union/union.ts
@@ -1,7 +1,7 @@
 // Code generated by 'guts'. DO NOT EDIT.
 
 // From union/union.go
-export interface Repeated<T extends string | string | number | number> {
+export interface Repeated<T extends string | number> {
     readonly Value: T;
 }
 

From 8992995219acbdfc977bc6d9b1ce5053b7e074a3 Mon Sep 17 00:00:00 2001
From: Carlos Cobo <carlos@remotely.works>
Date: Tue, 29 Jul 2025 17:01:32 +0200
Subject: [PATCH 2/2] emphasize this only works with literals

---
 bindings/declarations.go | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/bindings/declarations.go b/bindings/declarations.go
index 7b866e9..4fb74eb 100644
--- a/bindings/declarations.go
+++ b/bindings/declarations.go
@@ -73,22 +73,22 @@ func Simplify(p []*TypeParameter) ([]*TypeParameter, error) {
 			set[ref] = true
 
 			if union, ok := tp.Type.(*UnionType); ok {
-				simplifyUnion(union)
+				simplifyUnionLiterals(union)
 			}
 		}
 	}
 	return params, nil
 }
 
-func simplifyUnion(union *UnionType) *UnionType {
+func simplifyUnionLiterals(union *UnionType) *UnionType {
 	types := []ExpressionType{}
-	set := map[string]bool{}
+	literalSet := map[string]bool{}
 	for _, arg := range union.Types {
 		switch v := arg.(type) {
 		case *LiteralKeyword:
 			key := v.String()
-			if _, ok := set[key]; !ok {
-				set[key] = true
+			if _, ok := literalSet[key]; !ok {
+				literalSet[key] = true
 				types = append(types, arg)
 			}
 		default: