checker: make sure vweb actions return vweb.Result

vlib/v/checker/fn.v

@@ -410,6 +410,19 @@ fn (mut c Checker) fn_decl(mut node ast.FnDecl) {
 			c.table.fns[node.name].dep_names = dep_names
 		}
 	}
+
+	// vweb checks
+	if node.attrs.len > 0 && c.file.imports.filter(it.mod == 'vweb').len > 0 {
+		// If it's a vweb action (has the ['/url'] attribute), make sure it returns a vweb.Result
+		for attr in node.attrs {
+			if attr.name.starts_with('/') {
+				if c.table.sym(node.return_type).name != 'vweb.Result' {
+					c.error('vweb actions must return `vweb.Result`', node.pos)
+				}
+				break
+			}
+		}
+	}
 }
 
 // check_same_type_ignoring_pointers util function to check if the Types are the same, including all
@@ -2175,6 +2188,7 @@ fn (mut c Checker) method_call(mut node ast.CallExpr) ast.Type {
 			}
 		}
 	}
+
 	return node.return_type
 }
 

vlib/v/checker/tests/vweb_missing_result.out

@@ -0,0 +1,7 @@
+vlib/v/checker/tests/vweb_missing_result.vv:9:1: error: vweb actions must return `vweb.Result`
+    7 | // actions must return results
+    8 | ['/foo/:bar']
+    9 | pub fn (mut app App) foo(a string) {
+      | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+   10 | }
+   11 |

vlib/v/checker/tests/vweb_missing_result.vv

@@ -0,0 +1,15 @@
+import vweb
+
+struct App {
+	vweb.Context
+}
+
+// actions must return results
+['/foo/:bar']
+pub fn (mut app App) foo(a string) {
+}
+
+fn main() {
+	port := 8181
+	vweb.run[App](&App{}, port)
+}