From f34b921a8cb5728b1a8e1b7bcfcec6870971c869 Mon Sep 17 00:00:00 2001
From: Sebastian Spaink <3441183+sspaink@users.noreply.github.com>
Date: Wed, 19 Nov 2025 09:59:49 -0600
Subject: [PATCH] fix: support custom builtins in CompileModulesWithOpt (#8061)

Signed-off-by: Sebastian Spaink <sebastianspaink@gmail.com>
---
 v1/ast/compile_test.go  | 78 +++++++++++++++++++++++++++++++++++++++++
 v1/ast/compilehelper.go |  3 +-
 2 files changed, 80 insertions(+), 1 deletion(-)

diff --git a/v1/ast/compile_test.go b/v1/ast/compile_test.go
index 675acaf7bf..a8c593afd0 100644
--- a/v1/ast/compile_test.go
+++ b/v1/ast/compile_test.go
@@ -10662,6 +10662,84 @@ func TestCompilerCapabilitiesFeatures(t *testing.T) {
 	}
 }
 
+func TestCustomBuiltinWithCompileModulesWithOpt(t *testing.T) {
+	tests := []struct {
+		name              string
+		module            string
+		expectedErrorCode string
+		skipCapabilities  bool
+	}{
+		{
+			name: "custom builtin",
+			module: `package test
+
+			p if { bar(2) }`,
+		},
+		{
+			name: "missing custom builtin",
+			module: `package test
+	
+			p if { foo(1,2,x) }`,
+			expectedErrorCode: "rego_type_error",
+		},
+		{
+			name: "no capabilities, using custom builtin",
+			module: `package test
+
+			p if { bar(2) }`,
+			skipCapabilities:  true,
+			expectedErrorCode: "rego_type_error",
+		},
+		{
+			name: "no capabilities",
+			module: `package test
+				import rego.v1
+				p if { true }`,
+			skipCapabilities: true,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			customBuiltin := &Builtin{
+				Name: "bar",
+				Decl: types.NewFunction([]types.Type{types.N}, types.B),
+			}
+
+			capabilities := CapabilitiesForThisVersion()
+			capabilities.Builtins = append(capabilities.Builtins, customBuiltin)
+
+			var err error
+			if tc.skipCapabilities {
+				_, err = CompileModulesWithOpt(map[string]string{"x": tc.module}, CompileOpts{})
+			} else {
+				_, err = CompileModulesWithOpt(map[string]string{"x": tc.module}, CompileOpts{
+					ParserOptions: ParserOptions{
+						Capabilities: capabilities,
+					},
+				})
+			}
+
+			if tc.expectedErrorCode == "" && err != nil {
+				t.Fatal(err)
+			}
+			if tc.expectedErrorCode != "" {
+				if err == nil {
+					t.Fatalf("expected error code %s but got success", tc.expectedErrorCode)
+				}
+				var astError Errors
+				if errors.As(err, &astError) {
+					if astError[0].Code != tc.expectedErrorCode {
+						t.Fatalf("expected error code %s but got %s", tc.expectedErrorCode, astError[0].Code)
+					}
+				} else {
+					t.Fatal(err)
+				}
+			}
+		})
+	}
+}
+
 func TestCompilerCapabilitiesExtendedWithCustomBuiltins(t *testing.T) {
 
 	compiler := NewCompiler().WithCapabilities(&Capabilities{
diff --git a/v1/ast/compilehelper.go b/v1/ast/compilehelper.go
index 7d81d45e6d..4ea122f3cb 100644
--- a/v1/ast/compilehelper.go
+++ b/v1/ast/compilehelper.go
@@ -33,7 +33,8 @@ func CompileModulesWithOpt(modules map[string]string, opts CompileOpts) (*Compil
 
 	compiler := NewCompiler().
 		WithDefaultRegoVersion(opts.ParserOptions.RegoVersion).
-		WithEnablePrintStatements(opts.EnablePrintStatements)
+		WithEnablePrintStatements(opts.EnablePrintStatements).
+		WithCapabilities(opts.ParserOptions.Capabilities)
 	compiler.Compile(parsed)
 
 	if compiler.Failed() {