fix: deduplicate enum constant names that collapse to the same identifier

buildEnums deduplicated on EnumReplace(v), but the final constant name is
StructName(enumName+"_"+value), which collapses characters further (e.g. a
trailing underscore). So enum values like "A+" and "A-" reduced to distinct
EnumReplace outputs ("A" and "A_") that both mapped to the same constant
name, producing duplicate Go constants that fail to compile. Dedup on the final
constant name instead, falling back to value_<i> on collision.

Fixes #4515

Author: alliasgher

internal/codegen/golang/result.go

@@ -41,15 +41,24 @@ func buildEnums(req *plugin.GenerateRequest, options *opts.Options) []Enum {
 			seen := make(map[string]struct{}, len(enum.Vals))
 			for i, v := range enum.Vals {
 				value := EnumReplace(v)
-				if _, found := seen[value]; found || value == "" {
+				if value == "" {
 					value = fmt.Sprintf("value_%d", i)
 				}
+				// Dedup on the final constant name, not on EnumReplace(v):
+				// StructName further collapses characters (e.g. a trailing "_"),
+				// so distinct EnumReplace outputs like "A" and "A_" (from "A+"
+				// and "A-") can still map to the same constant name.
+				name := StructName(enumName+"_"+value, options)
+				if _, found := seen[name]; found {
+					value = fmt.Sprintf("value_%d", i)
+					name = StructName(enumName+"_"+value, options)
+				}
 				e.Constants = append(e.Constants, Constant{
-					Name:  StructName(enumName+"_"+value, options),
+					Name:  name,
 					Value: v,
 					Type:  e.Name,
 				})
-				seen[value] = struct{}{}
+				seen[name] = struct{}{}
 			}
 			enums = append(enums, e)
 		}

internal/codegen/golang/result_test.go

@@ -3,6 +3,7 @@ package golang
 import (
 	"testing"
 
+	"github.com/sqlc-dev/sqlc/internal/codegen/golang/opts"
 	"github.com/sqlc-dev/sqlc/internal/metadata"
 	"github.com/sqlc-dev/sqlc/internal/plugin"
 )
@@ -76,3 +77,42 @@ func TestPutOutColumns_AlwaysTrueWhenQueryHasColumns(t *testing.T) {
 		t.Error("should be true when we have columns")
 	}
 }
+
+// TestBuildEnums_DeduplicatesConstantNames covers enum values that differ only
+// by characters that get stripped or collapsed when building a Go identifier
+// (e.g. "A+" and "A-"), which previously produced duplicate constant names and
+// uncompilable output.
+func TestBuildEnums_DeduplicatesConstantNames(t *testing.T) {
+	req := &plugin.GenerateRequest{
+		Catalog: &plugin.Catalog{
+			DefaultSchema: "public",
+			Schemas: []*plugin.Schema{
+				{
+					Name: "public",
+					Enums: []*plugin.Enum{
+						{
+							Name: "blood_group_type",
+							Vals: []string{"A+", "A-", "B+", "B-", "AB+", "AB-", "O+", "O-"},
+						},
+					},
+				},
+			},
+		},
+	}
+
+	enums := buildEnums(req, &opts.Options{})
+	if len(enums) != 1 {
+		t.Fatalf("expected 1 enum, got %d", len(enums))
+	}
+	if got := len(enums[0].Constants); got != 8 {
+		t.Fatalf("expected 8 constants, got %d", got)
+	}
+
+	seen := make(map[string]string, 8)
+	for _, c := range enums[0].Constants {
+		if prev, dup := seen[c.Name]; dup {
+			t.Errorf("duplicate constant name %q for values %q and %q", c.Name, prev, c.Value)
+		}
+		seen[c.Name] = c.Value
+	}
+}