parser: improve the error message for unexpected keywords

vlib/v/parser/parser.v

@@ -425,7 +425,8 @@ fn (mut p Parser) check(expected token.Kind) {
 		if expected == .name {
 			p.name_error = true
 		}
-		p.error('unexpected `$p.tok.kind.str()`, expecting `$expected.str()`')
+		label := if token.is_key(p.tok.lit) { 'keyword ' } else { '' }
+		p.error('unexpected $label`$p.tok.kind.str()`, expecting `$expected.str()`')
 	}
 }
 

vlib/v/parser/tests/unexpected_keyword.out

@@ -0,0 +1,7 @@
+vlib/v/parser/tests/unexpected_keyword.vv:5:12: error: unexpected keyword `import`, expecting `(`
+    3 | }
+    4 | 
+    5 | fn (s Abc) import(name string) {
+      |            ~~~~~~
+    6 |     println(name)
+    7 | }

vlib/v/parser/tests/unexpected_keyword.vv

@@ -0,0 +1,12 @@
+struct Abc {
+	x int
+}
+
+fn (s Abc) import(name string) {
+	println(name)
+}
+
+fn main() {
+	s := Abc{}
+	s.import('lib')
+}