checker, cgen: fix interface embedding smartcast (fix #13296) (#15127)

examples/js_dom_cube/cube.js.v

@@ -197,7 +197,7 @@ const (
 	amortization = 0.95
 )
 
-fn get_webgl() (&JS.HTMLCanvasElement, JS.WebGLRenderingContext) {
+fn get_webgl() (JS.HTMLCanvasElement, JS.WebGLRenderingContext) {
 	JS.console.log(dom.document)
 	elem := dom.document.getElementById('myCanvas'.str) or { panic('cannot get canvas') }
 	match elem {

examples/js_dom_draw/draw.js.v

@@ -1,6 +1,6 @@
 import js.dom
 
-fn get_canvas(elem JS.HTMLElement) &JS.HTMLCanvasElement {
+fn get_canvas(elem JS.HTMLElement) JS.HTMLCanvasElement {
 	match elem {
 		JS.HTMLCanvasElement {
 			return elem

vlib/gg/gg.js.v

@@ -294,7 +294,7 @@ pub mut:
 	// *before* the current event was different
 }
 
-fn get_canvas(elem JS.HTMLElement) &JS.HTMLCanvasElement {
+fn get_canvas(elem JS.HTMLElement) JS.HTMLCanvasElement {
 	match elem {
 		JS.HTMLCanvasElement {
 			return elem

vlib/v/checker/checker.v

@@ -2903,7 +2903,11 @@ pub fn (mut c Checker) concat_expr(mut node ast.ConcatExpr) ast.Type {
 // smartcast takes the expression with the current type which should be smartcasted to the target type in the given scope
 fn (mut c Checker) smartcast(expr_ ast.Expr, cur_type ast.Type, to_type_ ast.Type, mut scope ast.Scope) {
 	sym := c.table.sym(cur_type)
-	to_type := if sym.kind == .interface_ { to_type_.ref() } else { to_type_ }
+	to_type := if sym.kind == .interface_ && c.table.sym(to_type_).kind != .interface_ {
+		to_type_.ref()
+	} else {
+		to_type_
+	}
 	mut expr := unsafe { expr_ }
 	match mut expr {
 		ast.SelectorExpr {

vlib/v/checker/if.v

@@ -311,8 +311,6 @@ fn (mut c Checker) smartcast_if_conds(node ast.Expr, mut scope ast.Scope) {
 				if left_sym.kind == .interface_ {
 					if right_sym.kind != .interface_ {
 						c.type_implements(right_type, expr_type, node.pos)
-					} else {
-						return
 					}
 				} else if !c.check_types(right_type, expr_type) && left_sym.kind != .sum_type {
 					expect_str := c.table.type_to_str(right_type)

vlib/v/gen/c/cgen.v

@@ -3331,6 +3331,12 @@ fn (mut g Gen) selector_expr(node ast.SelectorExpr) {
 							g.write('*')
 						}
 						cast_sym := g.table.sym(g.unwrap_generic(typ))
+						if field_sym.kind == .interface_ && cast_sym.kind == .interface_ {
+							ptr := '*'.repeat(field.typ.nr_muls())
+							dot := if node.expr_type.is_ptr() { '->' } else { '.' }
+							g.write('I_${field_sym.cname}_as_I_${cast_sym.cname}($ptr$node.expr$dot$node.field_name))')
+							return
+						} else {
 							if i != 0 {
 								dot := if field.typ.is_ptr() { '->' } else { '.' }
 								sum_type_deref_field += ')$dot'
@@ -3345,6 +3351,7 @@ fn (mut g Gen) selector_expr(node ast.SelectorExpr) {
 					}
 				}
 			}
+		}
 	} else if m := g.table.find_method(sym, node.field_name) {
 		mut has_embeds := false
 		if sym.info in [ast.Struct, ast.Aggregate] {
@@ -3894,6 +3901,10 @@ fn (mut g Gen) ident(node ast.Ident) {
 					}
 					for i, typ in node.obj.smartcasts {
 						cast_sym := g.table.sym(g.unwrap_generic(typ))
+						if obj_sym.kind == .interface_ && cast_sym.kind == .interface_ {
+							ptr := '*'.repeat(node.obj.typ.nr_muls())
+							g.write('I_${obj_sym.cname}_as_I_${cast_sym.cname}($ptr$node.name)')
+						} else {
 							mut is_ptr := false
 							if i == 0 {
 								g.write(name)
@@ -3908,6 +3919,7 @@ fn (mut g Gen) ident(node ast.Ident) {
 							} else {
 								g.write('${dot}_$cast_sym.cname')
 							}
+						}
 						g.write(')')
 					}
 					if is_auto_heap {

vlib/v/tests/interface_embedding_smartcast_test.v

@@ -0,0 +1,47 @@
+// Common interface to all error custom types.
+interface ESpeaker {
+	IError
+	speak() string
+}
+
+// One custom error implementation.
+struct MyError {
+	// Mandatory fields from IError.
+	msg  string
+	code int
+	// Custom field.
+	blah string
+}
+
+// Interface implementation for this example custom type.
+fn (e MyError) speak() string {
+	return e.blah
+}
+
+fn (e MyError) msg() string {
+	return e.msg
+}
+
+fn (e MyError) code() int {
+	return e.code
+}
+
+// An example function that returns a custom error.
+fn foo() ?string {
+	return IError(MyError{
+		msg: 'foo'
+		blah: 'world'
+	})
+}
+
+fn test_interface_embedding_smartcast() {
+	x := foo() or {
+		if err is ESpeaker {
+			err.speak()
+		} else {
+			'undefined'
+		}
+	}
+	println(x)
+	assert x == 'world'
+}

vlib/v/tests/interface_with_multi_nested_embed_1_test.v

@@ -34,8 +34,8 @@ mut:
 
 fn (mut w Window) init() {
 	for wd in w.initables {
-		if mut wd is Container {
-			mut c := wd as Container
+		if wd is Container {
+			mut c := unsafe { wd }
 			c.layout()
 		}
 	}