From f4251dded07e2fafc5a609241173504071e1d9e0 Mon Sep 17 00:00:00 2001
From: spaceface777 <spaceface7777@gmail.com>
Date: Tue, 21 Jul 2020 18:49:53 +0200
Subject: [PATCH] checker: suggest using `:=` when assigning to undefined
 variable (#5911)

---
 vlib/v/checker/checker.v                    | 7 ++++++-
 vlib/v/checker/tests/unknown_var_assign.out | 5 +++++
 vlib/v/checker/tests/unknown_var_assign.vv  | 3 +++
 vlib/v/parser/parser.v                      | 2 ++
 4 files changed, 16 insertions(+), 1 deletion(-)
 create mode 100644 vlib/v/checker/tests/unknown_var_assign.out
 create mode 100644 vlib/v/checker/tests/unknown_var_assign.vv

diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 1e0307c252..72816185a5 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -2524,7 +2524,12 @@ pub fn (mut c Checker) ident(mut ident ast.Ident) table.Type {
 			}
 			ident.mod = saved_mod
 		}
-		c.error('undefined ident: `$ident.name`', ident.pos)
+		if ident.tok_kind == .assign {
+			c.error('undefined ident: `$ident.name` (use `:=` to assign a variable)',
+				ident.pos)
+		} else {
+			c.error('undefined ident: `$ident.name`', ident.pos)
+		}
 	}
 	if c.table.known_type(ident.name) {
 		// e.g. `User`  in `json.decode(User, '...')`
diff --git a/vlib/v/checker/tests/unknown_var_assign.out b/vlib/v/checker/tests/unknown_var_assign.out
new file mode 100644
index 0000000000..c129fa4780
--- /dev/null
+++ b/vlib/v/checker/tests/unknown_var_assign.out
@@ -0,0 +1,5 @@
+vlib/v/checker/tests/unknown_var_assign.v:2:5: error: undefined ident: `x` (use `:=` to assign a variable)
+    1 | fn main() {
+    2 |     x = 'hello v'
+      |     ^
+    3 | }
diff --git a/vlib/v/checker/tests/unknown_var_assign.vv b/vlib/v/checker/tests/unknown_var_assign.vv
new file mode 100644
index 0000000000..d7ed5306d5
--- /dev/null
+++ b/vlib/v/checker/tests/unknown_var_assign.vv
@@ -0,0 +1,3 @@
+fn main() {
+    x = 'hello v'
+}
diff --git a/vlib/v/parser/parser.v b/vlib/v/parser/parser.v
index 10b2af49f3..a13bb93c32 100644
--- a/vlib/v/parser/parser.v
+++ b/vlib/v/parser/parser.v
@@ -850,6 +850,7 @@ pub fn (mut p Parser) parse_ident(language table.Language) ast.Ident {
 		mut name := p.check_name()
 		if name == '_' {
 			return ast.Ident{
+				tok_kind: p.tok.kind
 				name: '_'
 				kind: .blank_ident
 				pos: pos
@@ -866,6 +867,7 @@ pub fn (mut p Parser) parse_ident(language table.Language) ast.Ident {
 			name = '${p.expr_mod}.$name'
 		}
 		return ast.Ident{
+			tok_kind: p.tok.kind
 			kind: .unresolved
 			name: name
 			language: language