From c53757848195bf0852a5651c2531b2a359bb2810 Mon Sep 17 00:00:00 2001
From: Nick Treleaven <n@trelsoft.com>
Date: Mon, 1 Feb 2021 14:18:03 +0000
Subject: [PATCH] checker: ensure `expr` is an lvalue with `Struct{...expr`
 (#8489)

---
 vlib/v/checker/checker.v                      | 13 +++++---
 .../tests/struct_init_update_type_err.out     | 31 ++++++++++++++++---
 .../tests/struct_init_update_type_err.vv      | 17 ++++++++--
 3 files changed, 49 insertions(+), 12 deletions(-)

diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index c5429fe32a..fd74e50ab1 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -680,12 +680,17 @@ pub fn (mut c Checker) struct_init(mut struct_init ast.StructInit) table.Type {
 	if struct_init.has_update_expr {
 		update_type := c.expr(struct_init.update_expr)
 		struct_init.update_expr_type = update_type
-		update_sym := c.table.get_type_symbol(update_type)
-		sym := c.table.get_type_symbol(struct_init.typ)
-		if update_sym.kind != .struct_ {
-			c.error('expected struct `$sym.name`, found `$update_sym.name`', struct_init.update_expr.position())
+		if c.table.type_kind(update_type) != .struct_ {
+			s := c.table.type_to_str(update_type)
+			c.error('expected struct, found `$s`', struct_init.update_expr.position())
 		} else if update_type != struct_init.typ {
+			sym := c.table.get_type_symbol(struct_init.typ)
+			update_sym := c.table.get_type_symbol(update_type)
 			c.error('expected struct `$sym.name`, found struct `$update_sym.name`', struct_init.update_expr.position())
+		} else if !struct_init.update_expr.is_lvalue() {
+			// cgen will repeat `update_expr` for each field
+			// so enforce an lvalue for efficiency
+			c.error('expression is not an lvalue', struct_init.update_expr.position())
 		}
 	}
 	return struct_init.typ
diff --git a/vlib/v/checker/tests/struct_init_update_type_err.out b/vlib/v/checker/tests/struct_init_update_type_err.out
index c75fb0abdb..b8749f9e78 100644
--- a/vlib/v/checker/tests/struct_init_update_type_err.out
+++ b/vlib/v/checker/tests/struct_init_update_type_err.out
@@ -1,7 +1,28 @@
-vlib/v/checker/tests/struct_init_update_type_err.vv:11:6: error: expected struct `Foo`, found `int`
-    9 |     f3 := 2
+vlib/v/checker/tests/struct_init_update_type_err.vv:11:6: error: expected struct, found `int`
+    9 |     i := 2
    10 |     _ := Foo{
-   11 |         ...f3
-      |            ~~
+   11 |         ...i
+      |            ^
    12 |         name: 'f2'
-   13 |     }
\ No newline at end of file
+   13 |     }
+vlib/v/checker/tests/struct_init_update_type_err.vv:16:6: error: expected struct, found `&int`
+   14 |     p := &i
+   15 |     _ = Foo{
+   16 |         ...p
+      |            ^
+   17 |     }
+   18 |     f2 := Foo2{}
+vlib/v/checker/tests/struct_init_update_type_err.vv:20:6: error: expected struct `Foo`, found struct `Foo2`
+   18 |     f2 := Foo2{}
+   19 |     _ = Foo{
+   20 |         ...f2
+      |            ~~
+   21 |     }
+   22 |     _ = Foo{
+vlib/v/checker/tests/struct_init_update_type_err.vv:23:6: error: expression is not an lvalue
+   21 |     }
+   22 |     _ = Foo{
+   23 |         ...Foo{}
+      |            ~~~~~
+   24 |     }
+   25 | }
diff --git a/vlib/v/checker/tests/struct_init_update_type_err.vv b/vlib/v/checker/tests/struct_init_update_type_err.vv
index a7988d9da7..2bd876c786 100644
--- a/vlib/v/checker/tests/struct_init_update_type_err.vv
+++ b/vlib/v/checker/tests/struct_init_update_type_err.vv
@@ -3,13 +3,24 @@ struct Foo {
 	age int
 }
 
-struct Foo2 {}
+struct Foo2 {b bool}
 
 fn main() {
-	f3 := 2
+	i := 2
 	_ := Foo{
-		...f3
+		...i
 		name: 'f2'
 	}
+	p := &i
+	_ = Foo{
+		...p
+	}
+	f2 := Foo2{}
+	_ = Foo{
+		...f2
+	}
+	_ = Foo{
+		...Foo{}
+	}
 }