From 49aac93d874419bd12cd224d401ea8e12bc5fd6a Mon Sep 17 00:00:00 2001
From: Swastik Baranwal <swstkbaranwal@gmail.com>
Date: Sat, 8 Oct 2022 21:57:30 +0530
Subject: [PATCH] checker: disallow literals on the left side of assignments
 (#15999)

---
 vlib/v/ast/ast.v                              |  2 +-
 vlib/v/checker/assign.v                       |  4 ++
 .../tests/invalid_literal_assign_err.out      | 62 +++++++++++++++++++
 .../tests/invalid_literal_assign_err.vv       | 13 ++++
 4 files changed, 80 insertions(+), 1 deletion(-)
 create mode 100644 vlib/v/checker/tests/invalid_literal_assign_err.out
 create mode 100644 vlib/v/checker/tests/invalid_literal_assign_err.vv

diff --git a/vlib/v/ast/ast.v b/vlib/v/ast/ast.v
index f7c920f49..ba83aacd3 100644
--- a/vlib/v/ast/ast.v
+++ b/vlib/v/ast/ast.v
@@ -2227,7 +2227,7 @@ fn gen_all_registers(mut t Table, without_numbers []string, with_numbers map[str
 // is `expr` a literal, i.e. it does not depend on any other declarations (C compile time constant)
 pub fn (expr Expr) is_literal() bool {
 	match expr {
-		BoolLiteral, CharLiteral, FloatLiteral, IntegerLiteral {
+		BoolLiteral, CharLiteral, FloatLiteral, IntegerLiteral, StringLiteral, StringInterLiteral {
 			return true
 		}
 		PrefixExpr {
diff --git a/vlib/v/checker/assign.v b/vlib/v/checker/assign.v
index 3245c69d2..ea58ed8f3 100644
--- a/vlib/v/checker/assign.v
+++ b/vlib/v/checker/assign.v
@@ -323,6 +323,10 @@ pub fn (mut c Checker) assign_stmt(mut node ast.AssignStmt) {
 				if is_decl {
 					c.error('non-name `$left` on left side of `:=`', left.pos())
 				}
+
+				if node.op == .assign && (left.is_literal() || left is ast.StructInit) {
+					c.error('non-name literal value `$left` on left side of `=`', left.pos())
+				}
 			}
 		}
 		left_type_unwrapped := c.unwrap_generic(ast.mktyp(left_type))
diff --git a/vlib/v/checker/tests/invalid_literal_assign_err.out b/vlib/v/checker/tests/invalid_literal_assign_err.out
new file mode 100644
index 000000000..9d3075f2a
--- /dev/null
+++ b/vlib/v/checker/tests/invalid_literal_assign_err.out
@@ -0,0 +1,62 @@
+vlib/v/checker/tests/invalid_literal_assign_err.vv:4:2: error: non-name literal value `1` on left side of `=`
+    2 | 
+    3 | fn main() {
+    4 |     1 = 2
+      |     ^
+    5 |     u8(1) = u8(2)
+    6 |     1.0 = 2.0
+vlib/v/checker/tests/invalid_literal_assign_err.vv:5:2: error: non-name literal value `u8(1)` on left side of `=`
+    3 | fn main() {
+    4 |     1 = 2
+    5 |     u8(1) = u8(2)
+      |     ~~~~~
+    6 |     1.0 = 2.0
+    7 |     'str' = 'string'
+vlib/v/checker/tests/invalid_literal_assign_err.vv:6:2: error: non-name literal value `1.0` on left side of `=`
+    4 |     1 = 2
+    5 |     u8(1) = u8(2)
+    6 |     1.0 = 2.0
+      |     ~~~
+    7 |     'str' = 'string'
+    8 |     `a` = `b`
+vlib/v/checker/tests/invalid_literal_assign_err.vv:7:2: error: non-name literal value `'str'` on left side of `=`
+    5 |     u8(1) = u8(2)
+    6 |     1.0 = 2.0
+    7 |     'str' = 'string'
+      |     ~~~~~
+    8 |     `a` = `b`
+    9 |     Foo{} = Foo{}
+vlib/v/checker/tests/invalid_literal_assign_err.vv:8:2: error: non-name literal value ``a`` on left side of `=`
+    6 |     1.0 = 2.0
+    7 |     'str' = 'string'
+    8 |     `a` = `b`
+      |     ~~~
+    9 |     Foo{} = Foo{}
+   10 |     true = false
+vlib/v/checker/tests/invalid_literal_assign_err.vv:9:2: error: non-name literal value `Foo{....}` on left side of `=`
+    7 |     'str' = 'string'
+    8 |     `a` = `b`
+    9 |     Foo{} = Foo{}
+      |     ~~~~~
+   10 |     true = false
+   11 |     3 + 5 = 3 & 4
+vlib/v/checker/tests/invalid_literal_assign_err.vv:10:2: error: non-name literal value `true` on left side of `=`
+    8 |     `a` = `b`
+    9 |     Foo{} = Foo{}
+   10 |     true = false
+      |     ~~~~
+   11 |     3 + 5 = 3 & 4
+   12 |     (3 + 3.5) = 4 + 6.4
+vlib/v/checker/tests/invalid_literal_assign_err.vv:11:2: error: non-name literal value `3 + 5` on left side of `=`
+    9 |     Foo{} = Foo{}
+   10 |     true = false
+   11 |     3 + 5 = 3 & 4
+      |     ~~~~~
+   12 |     (3 + 3.5) = 4 + 6.4
+   13 | }
+vlib/v/checker/tests/invalid_literal_assign_err.vv:12:2: error: non-name literal value `(3 + 3.5)` on left side of `=`
+   10 |     true = false
+   11 |     3 + 5 = 3 & 4
+   12 |     (3 + 3.5) = 4 + 6.4
+      |     ~~~~~~~~~
+   13 | }
diff --git a/vlib/v/checker/tests/invalid_literal_assign_err.vv b/vlib/v/checker/tests/invalid_literal_assign_err.vv
new file mode 100644
index 000000000..78f3238d0
--- /dev/null
+++ b/vlib/v/checker/tests/invalid_literal_assign_err.vv
@@ -0,0 +1,13 @@
+struct Foo {}
+
+fn main() {
+	1 = 2
+	u8(1) = u8(2)
+	1.0 = 2.0
+	'str' = 'string'
+	`a` = `b`
+	Foo{} = Foo{}
+	true = false
+	3 + 5 = 3 & 4
+	(3 + 3.5) = 4 + 6.4
+}
-- 
2.39.5