wasm: resolve fixed-array .len instead of aborting with "could not find field len" (#27518)

Author: enghitalo

vlib/v/gen/wasm/gen.v

@@ -1016,7 +1016,13 @@ pub fn (mut g Gen) expr(node ast.Expr, expected ast.Type) {
 			g.get(v)
 		}
 		ast.SelectorExpr {
-			if v := g.get_var_from_expr(node) {
+			final := g.table.final_sym(node.expr_type)
+			if node.field_name == 'len' && final.info is ast.ArrayFixed {
+				// a fixed array's `.len` is a compile-time constant; the checker
+				// types it as `int` but emits no field, so resolve it here rather
+				// than aborting in get_field_offset ("could not find field len").
+				g.func.i32_const(i32(final.info.size))
+			} else if v := g.get_var_from_expr(node) {
 				if g.needs_address {
 					if !v.is_address {
 						g.v_error("cannot take the address of a value that doesn't live on the stack. this is a current limitation.",

vlib/v/gen/wasm/tests/arrays.vv

@@ -62,6 +62,13 @@ fn selector_index_assign() {
 	println(app.frame[app.idx])
 }
 
+fn fixed_array_len() {
+	a := [10, 12, 150]!
+	println(a.len)
+	b := [8]int{}
+	println(b.len)
+}
+
 fn main() {
 	println('--- static_arrays()')
 	a, b, c := static_arrays()
@@ -83,4 +90,7 @@ fn main() {
 
 	println('--- selector_index_assign()')
 	selector_index_assign()
+
+	println('--- fixed_array_len()')
+	fixed_array_len()
 }

vlib/v/gen/wasm/tests/arrays.vv.out

@@ -16,3 +16,6 @@
 0
 123
 123
+--- fixed_array_len()
+3
+8