From 9ca89235b544cb153d685d9e493b53cb9da4281d Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Wed, 15 Apr 2026 15:17:45 +0300
Subject: [PATCH] checker: fix checker error for veb handler param type (fixes
 #24870)

---
 vlib/v/checker/fn.v                           | 18 +++++++++++++++++-
 .../tests/veb_handler_param_type_err.out      |  7 +++++++
 .../tests/veb_handler_param_type_err.vv       | 19 +++++++++++++++++++
 vlib/veb/README.md                            |  2 ++
 4 files changed, 45 insertions(+), 1 deletion(-)
 create mode 100644 vlib/v/checker/tests/veb_handler_param_type_err.out
 create mode 100644 vlib/v/checker/tests/veb_handler_param_type_err.vv

diff --git a/vlib/v/checker/fn.v b/vlib/v/checker/fn.v
index 1a2e790ef..87b588068 100644
--- a/vlib/v/checker/fn.v
+++ b/vlib/v/checker/fn.v
@@ -839,8 +839,9 @@ fn (mut c Checker) fn_decl(mut node ast.FnDecl) {
 	// Register implicit context var
 	typ_veb_result := c.table.get_veb_result_type_idx() // c.table.find_type('veb.Result')
 	if node.is_method && node.return_type == typ_veb_result {
+		is_veb_app_method := !c.has_veb_context(node.receiver.typ)
 		for param in node.params[1..] {
-			if c.has_veb_context(param.typ) && !param.is_mut {
+			if is_veb_app_method && c.has_veb_context(param.typ) && !param.is_mut {
 				c.error('veb app method `${node.name}` must declare context parameter `${param.name}` as mutable, e.g. `mut ${param.name} ${c.table.type_to_str(param.typ)}`',
 					param.pos)
 				break
@@ -888,6 +889,15 @@ fn (mut c Checker) fn_decl(mut node ast.FnDecl) {
 			is_mut:       true
 			is_stack_obj: false // true
 		})
+		if is_veb_app_method {
+			for param in node.params[1..] {
+				if c.has_veb_context(param.typ) || c.supports_veb_string_bound_param(param.typ) {
+					continue
+				}
+				c.error('veb app method `${node.name}` parameter `${param.name}` has unsupported type `${c.table.type_to_str(param.typ)}`; parameters after the context are populated from strings and must be `string`, integer, or `bool`',
+					param.pos)
+			}
+		}
 	}
 	c.stmts(mut node.stmts)
 	node_has_top_return := has_top_return(node.stmts)
@@ -5117,6 +5127,12 @@ fn (mut c Checker) has_veb_context(typ ast.Type) bool {
 	return false
 }
 
+fn (mut c Checker) supports_veb_string_bound_param(typ ast.Type) bool {
+	unaliased_typ := c.table.unalias_num_type(c.unwrap_generic(typ))
+	return unaliased_typ == ast.string_type || unaliased_typ.is_int()
+		|| unaliased_typ.idx() == ast.bool_type_idx
+}
+
 fn (mut c Checker) check_variadic_arg(arg_expr ast.Expr, typ ast.Type, expected_type ast.Type, param_typ ast.Type,
 	arg_num int, fn_name string, is_method bool, fn_is_variadic bool, is_single_array_arg bool,
 	is_generic_fn bool, call_pos token.Pos, arg_pos token.Pos) {
diff --git a/vlib/v/checker/tests/veb_handler_param_type_err.out b/vlib/v/checker/tests/veb_handler_param_type_err.out
new file mode 100644
index 000000000..05413e7c7
--- /dev/null
+++ b/vlib/v/checker/tests/veb_handler_param_type_err.out
@@ -0,0 +1,7 @@
+vlib/v/checker/tests/veb_handler_param_type_err.vv:17:42: error: veb app method `index` parameter `params` has unsupported type `Params`; parameters after the context are populated from strings and must be `string`, integer, or `bool`
+   15 | fn main() {}
+   16 | 
+   17 | pub fn (app &App) index(mut ctx Context, params Params) veb.Result {
+      |                                          ~~~~~~
+   18 |     return veb.no_result()
+   19 | }
diff --git a/vlib/v/checker/tests/veb_handler_param_type_err.vv b/vlib/v/checker/tests/veb_handler_param_type_err.vv
new file mode 100644
index 000000000..b534efb3d
--- /dev/null
+++ b/vlib/v/checker/tests/veb_handler_param_type_err.vv
@@ -0,0 +1,19 @@
+module main
+
+import veb
+
+struct Params {
+	offset int
+}
+
+pub struct Context {
+	veb.Context
+}
+
+pub struct App {}
+
+fn main() {}
+
+pub fn (app &App) index(mut ctx Context, params Params) veb.Result {
+	return veb.no_result()
+}
diff --git a/vlib/veb/README.md b/vlib/veb/README.md
index 83ed23874..d87263ffc 100644
--- a/vlib/veb/README.md
+++ b/vlib/veb/README.md
@@ -231,6 +231,8 @@ parameters are passed as arguments. V will cast the parameter to any of V's prim
 To pass a parameter to an endpoint, you simply define it inside an attribute, e. g.
 `@['/hello/:user]`.
 After it is defined in the attribute, you have to add it as a function parameter.
+Parameters after `ctx` are populated from strings, so they currently must be `string`,
+integer, or `bool`.
 
 **Example:**
 
-- 
2.39.5