fix: Return an error instead of generating duplicate Go names (#2962)

* fix: Return an error instead of generating duplicate Go names

Resolves #588

* Improve error messages

---------

Co-authored-by: Kyle Conroy <kyle@sqlc.dev>

Author: andrewmbenton

internal/codegen/golang/gen.go

@@ -124,9 +124,40 @@ func Generate(ctx context.Context, req *plugin.GenerateRequest) (*plugin.Generat
 		enums, structs = filterUnusedStructs(enums, structs, queries)
 	}
 
+	if err := validate(options, enums, structs, queries); err != nil {
+		return nil, err
+	}
+
 	return generate(req, options, enums, structs, queries)
 }
 
+func validate(options *opts.Options, enums []Enum, structs []Struct, queries []Query) error {
+	enumNames := make(map[string]struct{})
+	for _, enum := range enums {
+		enumNames[enum.Name] = struct{}{}
+		enumNames["Null"+enum.Name] = struct{}{}
+	}
+	structNames := make(map[string]struct{})
+	for _, struckt := range structs {
+		if _, ok := enumNames[struckt.Name]; ok {
+			return fmt.Errorf("struct name conflicts with enum name: %s", struckt.Name)
+		}
+		structNames[struckt.Name] = struct{}{}
+	}
+	if !options.EmitExportedQueries {
+		return nil
+	}
+	for _, query := range queries {
+		if _, ok := enumNames[query.ConstantName]; ok {
+			return fmt.Errorf("query constant name conflicts with enum name: %s", query.ConstantName)
+		}
+		if _, ok := structNames[query.ConstantName]; ok {
+			return fmt.Errorf("query constant name conflicts with struct name: %s", query.ConstantName)
+		}
+	}
+	return nil
+}
+
 func generate(req *plugin.GenerateRequest, options *opts.Options, enums []Enum, structs []Struct, queries []Query) (*plugin.GenerateResponse, error) {
 	i := &importer{
 		Options: options,

internal/endtoend/testdata/duplicate_go_names/enum/query.sql

@@ -0,0 +1,2 @@
+-- name: GetFoos :many
+SELECT * FROM foos;

internal/endtoend/testdata/duplicate_go_names/enum/schema.sql

@@ -0,0 +1,3 @@
+CREATE TYPE foo AS ENUM ();
+
+CREATE TABLE foos ();

internal/endtoend/testdata/duplicate_go_names/enum/sqlc.yaml

@@ -0,0 +1,8 @@
+version: "2"
+sql:
+- schema: "schema.sql"
+  queries: "query.sql"
+  engine: "postgresql"
+  gen:
+    go:
+      out: "db"

internal/endtoend/testdata/duplicate_go_names/enum/stderr.txt

@@ -0,0 +1,2 @@
+# package 
+error generating code: struct name conflicts with enum name: Foo

internal/endtoend/testdata/duplicate_go_names/null_enum/query.sql

@@ -0,0 +1,2 @@
+-- name: GetFoos :many
+SELECT * FROM null_foos;

internal/endtoend/testdata/duplicate_go_names/null_enum/schema.sql

@@ -0,0 +1,3 @@
+CREATE TYPE foo AS ENUM ();
+
+CREATE TABLE null_foos ();

internal/endtoend/testdata/duplicate_go_names/null_enum/sqlc.yaml

@@ -0,0 +1,8 @@
+version: "2"
+sql:
+- schema: "schema.sql"
+  queries: "query.sql"
+  engine: "postgresql"
+  gen:
+    go:
+      out: "db"

internal/endtoend/testdata/duplicate_go_names/null_enum/stderr.txt

@@ -0,0 +1,2 @@
+# package 
+error generating code: struct name conflicts with enum name: NullFoo

internal/endtoend/testdata/duplicate_go_names/query_constant/query.sql

@@ -0,0 +1,2 @@
+-- name: Foo :one
+SELECT 1;