From efc91ed908899dd0f8dd0ac2842f70f9412be8b3 Mon Sep 17 00:00:00 2001
From: Ville Vesilehto <ville@vesilehto.fi>
Date: Sun, 30 Nov 2025 22:22:56 +0200
Subject: [PATCH] fix(vm): show func for safe calls in disassembly

Previously, safe builtin functions (OpCallSafe) were pushed to the stack
as constants (OpPush), causing the disassembler/debugger to display
their memory address (e.g., 0x140000...) instead of their name (e.g.,
concat).

This change updates the compiler to store the function name in debugInfo
when emitting OpCallSafe. The VM's disassembler now checks debugInfo for
OpPush arguments and displays the stored name if available.

Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>
---
 compiler/compiler.go          |  4 +++-
 test/issues/567/issue_test.go | 25 +++++++++++++++++++++++++
 vm/program.go                 |  3 +++
 3 files changed, 31 insertions(+), 1 deletion(-)
 create mode 100644 test/issues/567/issue_test.go

diff --git a/compiler/compiler.go b/compiler/compiler.go
index 83b19a885..fe1c00c4d 100644
--- a/compiler/compiler.go
+++ b/compiler/compiler.go
@@ -1103,7 +1103,9 @@ func (c *compiler) BuiltinNode(node *ast.BuiltinNode) {
 		if f.Fast != nil {
 			c.emit(OpCallBuiltin1, id)
 		} else if f.Safe != nil {
-			c.emit(OpPush, c.addConstant(f.Safe))
+			id := c.addConstant(f.Safe)
+			c.emit(OpPush, id)
+			c.debugInfo[fmt.Sprintf("const_%d", id)] = node.Name
 			c.emit(OpCallSafe, len(node.Arguments))
 		} else if f.Func != nil {
 			c.emitFunction(f, len(node.Arguments))
diff --git a/test/issues/567/issue_test.go b/test/issues/567/issue_test.go
new file mode 100644
index 000000000..b5c76d83e
--- /dev/null
+++ b/test/issues/567/issue_test.go
@@ -0,0 +1,25 @@
+package expr_test
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+
+	"github.com/expr-lang/expr"
+	"github.com/expr-lang/expr/internal/testify/require"
+)
+
+func TestIssue567(t *testing.T) {
+	program, err := expr.Compile("concat(1..2, 3..4)")
+	require.NoError(t, err)
+
+	var buf bytes.Buffer
+	program.DisassembleWriter(&buf)
+	output := buf.String()
+
+	// Check if "concat" is mentioned in the output
+	require.True(t, strings.Contains(output, "concat"), "expected 'concat' in disassembly output")
+
+	// It should appear as a pushed constant
+	require.True(t, strings.Contains(output, "OpPush\t<4>\tconcat"), "expected 'OpPush <4> concat' in disassembly output")
+}
diff --git a/vm/program.go b/vm/program.go
index 15ce26f5b..d146cc139 100644
--- a/vm/program.go
+++ b/vm/program.go
@@ -112,6 +112,9 @@ func (program *Program) DisassembleWriter(w io.Writer) {
 			} else {
 				c = "out of range"
 			}
+			if name, ok := program.debugInfo[fmt.Sprintf("const_%d", arg)]; ok {
+				c = name
+			}
 			if r, ok := c.(*regexp.Regexp); ok {
 				c = r.String()
 			}