From 69f31d8d5c4accf766e41b46cd7a2758a377add7 Mon Sep 17 00:00:00 2001
From: Florian Blasius <flovanpt@posteo.de>
Date: Mon, 2 Aug 2021 06:12:29 +0200
Subject: [PATCH] checker: check int literal to enum cast (fix #10125) (#10348)

---
 vlib/v/ast/table.v                 |  6 +++++
 vlib/v/checker/checker.v           | 35 ++++++++++++++++++++++++++++++
 vlib/v/checker/tests/enum_cast.out |  6 +++++
 vlib/v/checker/tests/enum_cast.vv  |  7 ++++++
 vlib/v/parser/parser.v             |  7 +++++-
 5 files changed, 60 insertions(+), 1 deletion(-)
 create mode 100644 vlib/v/checker/tests/enum_cast.out
 create mode 100644 vlib/v/checker/tests/enum_cast.vv

diff --git a/vlib/v/ast/table.v b/vlib/v/ast/table.v
index 4b19dcf7fc..f97238a941 100644
--- a/vlib/v/ast/table.v
+++ b/vlib/v/ast/table.v
@@ -35,6 +35,7 @@ pub mut:
 	cur_fn             &FnDecl = 0 // previously stored in Checker.cur_fn and Gen.cur_fn
 	cur_concrete_types []Type  // current concrete types, e.g. <int, string>
 	gostmts            int     // how many `go` statements there were in the parsed files.
+	enum_decls         map[string]EnumDecl
 	// When table.gostmts > 0, __VTHREADS__ is defined, which can be checked with `$if threads {`
 }
 
@@ -657,6 +658,11 @@ pub fn (mut t Table) register_type_symbol(typ TypeSymbol) int {
 	return typ_idx
 }
 
+[inline]
+pub fn (mut t Table) register_enum_decl(enum_decl EnumDecl) {
+	t.enum_decls[enum_decl.name] = enum_decl
+}
+
 pub fn (t &Table) known_type(name string) bool {
 	return t.find_type_idx(name) != 0
 }
diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 6b6b6be6ad..dd179c99c2 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -5607,6 +5607,41 @@ pub fn (mut c Checker) cast_expr(mut node ast.CastExpr) ast.Type {
 	if node.has_arg {
 		c.expr(node.arg)
 	}
+
+	// checks on int literal to enum cast if the value represents a value on the enum
+	if to_type_sym.kind == .enum_ {
+		if node.expr is ast.IntegerLiteral {
+			enum_typ_name := c.table.get_type_name(node.typ)
+			node_val := (node.expr as ast.IntegerLiteral).val.int()
+
+			if enum_decl := c.table.enum_decls[to_type_sym.name] {
+				mut in_range := false
+				mut enum_val := 0
+
+				for enum_field in enum_decl.fields {
+					// check if the field of the enum value is an integer literal
+					if enum_field.expr is ast.IntegerLiteral {
+						enum_val = enum_field.expr.val.int()
+					}
+
+					if node_val == enum_val {
+						in_range = true
+						break
+					}
+
+					enum_val += 1
+				}
+
+				if !in_range {
+					c.warn('$node_val does not represents a value of enum $enum_typ_name',
+						node.pos)
+				}
+			}
+		}
+	}
+
+	node.typname = c.table.get_type_symbol(node.typ).name
+
 	return node.typ
 }
 
diff --git a/vlib/v/checker/tests/enum_cast.out b/vlib/v/checker/tests/enum_cast.out
new file mode 100644
index 0000000000..053fe1b470
--- /dev/null
+++ b/vlib/v/checker/tests/enum_cast.out
@@ -0,0 +1,6 @@
+vlib/v/checker/tests/enum_cast.vv:6:13: error: 12 does not represents a value of enum Color
+    4 |     println(Color(0))
+    5 |     println(Color(10))
+    6 |     println(Color(12))
+      |             ~~~~~~~~~
+    7 | }
diff --git a/vlib/v/checker/tests/enum_cast.vv b/vlib/v/checker/tests/enum_cast.vv
new file mode 100644
index 0000000000..40e9ec7e84
--- /dev/null
+++ b/vlib/v/checker/tests/enum_cast.vv
@@ -0,0 +1,7 @@
+enum Color { red green = 10 blue }
+
+fn main() {
+    println(Color(0))
+    println(Color(10))
+    println(Color(12))
+}
\ No newline at end of file
diff --git a/vlib/v/parser/parser.v b/vlib/v/parser/parser.v
index f4575e8986..e17295e67c 100644
--- a/vlib/v/parser/parser.v
+++ b/vlib/v/parser/parser.v
@@ -3097,7 +3097,8 @@ fn (mut p Parser) enum_decl() ast.EnumDecl {
 		p.error_with_pos('cannot register enum `$name`, another type with this name exists',
 			end_pos)
 	}
-	return ast.EnumDecl{
+
+	enum_decl := ast.EnumDecl{
 		name: name
 		is_pub: is_pub
 		is_flag: is_flag
@@ -3107,6 +3108,10 @@ fn (mut p Parser) enum_decl() ast.EnumDecl {
 		attrs: p.attrs
 		comments: enum_decl_comments
 	}
+
+	p.table.register_enum_decl(enum_decl)
+
+	return enum_decl
 }
 
 fn (mut p Parser) type_decl() ast.TypeDecl {