From 178dfbf872faa8e759f28a764ef448b5f0286ac7 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Wed, 25 Mar 2026 16:42:19 +0300
Subject: [PATCH] checker: fix duplicate case value for match with u8 and int
 (fixes #26627)

---
 vlib/v/checker/match.v                        | 62 +++++++++++++++++--
 ...ch_duplicate_branch_mixed_int_literals.out | 14 +++++
 ...tch_duplicate_branch_mixed_int_literals.vv | 29 +++++++++
 3 files changed, 101 insertions(+), 4 deletions(-)
 create mode 100644 vlib/v/checker/tests/match_duplicate_branch_mixed_int_literals.out
 create mode 100644 vlib/v/checker/tests/match_duplicate_branch_mixed_int_literals.vv

diff --git a/vlib/v/checker/match.v b/vlib/v/checker/match.v
index fd5824105..14cdb3bae 100644
--- a/vlib/v/checker/match.v
+++ b/vlib/v/checker/match.v
@@ -570,15 +570,51 @@ fn (mut c Checker) check_match_branch_last_stmt(last_stmt ast.ExprStmt, ret_type
 	}
 }
 
+fn char_literal_number_value(value string) ?i64 {
+	if value.len == 2 && value[0] == `\\` {
+		return match value[1] {
+			`a` { 7 }
+			`b` { 8 }
+			`t` { 9 }
+			`n` { 10 }
+			`v` { 11 }
+			`f` { 12 }
+			`r` { 13 }
+			`e` { 27 }
+			`$` { 36 }
+			`"` { 34 }
+			`'` { 39 }
+			`?` { 63 }
+			`@` { 64 }
+			`\\` { 92 }
+			`\`` { 96 }
+			`{` { 123 }
+			`}` { 125 }
+			else { none }
+		}
+	}
+	runes := value.runes()
+	if runes.len == 1 {
+		return runes[0]
+	}
+	return none
+}
+
 fn (mut c Checker) get_comptime_number_value(mut expr ast.Expr) ?i64 {
+	if mut expr is ast.ParExpr {
+		return c.get_comptime_number_value(mut expr.expr)
+	}
+	if mut expr is ast.PrefixExpr && expr.op == .minus {
+		return -c.get_comptime_number_value(mut expr.right)?
+	}
 	if mut expr is ast.CharLiteral {
-		return expr.val[0]
+		return char_literal_number_value(expr.val)
 	}
 	if mut expr is ast.IntegerLiteral {
 		return expr.val.i64()
 	}
-	if mut expr is ast.CastExpr && expr.expr is ast.IntegerLiteral {
-		return expr.expr.val.i64()
+	if mut expr is ast.CastExpr {
+		return c.get_comptime_number_value(mut expr.expr)
 	}
 	if mut expr is ast.Ident {
 		if mut obj := c.table.global_scope.find_const(expr.full_name()) {
@@ -591,6 +627,24 @@ fn (mut c Checker) get_comptime_number_value(mut expr ast.Expr) ?i64 {
 	return none
 }
 
+fn (mut c Checker) get_match_case_int_key(mut expr ast.Expr, cond_sym ast.TypeSymbol) ?string {
+	if !cond_sym.is_int() {
+		return none
+	}
+	if value := c.get_comptime_number_value(mut expr) {
+		return value.str()
+	}
+	if value := c.eval_comptime_const_expr(expr, 0) {
+		if signed_value := value.i64() {
+			return signed_value.str()
+		}
+		if unsigned_value := value.u64() {
+			return unsigned_value.str()
+		}
+	}
+	return none
+}
+
 fn (mut c Checker) match_exprs(mut node ast.MatchExpr, cond_type_sym ast.TypeSymbol) {
 	c.expected_type = node.expected_type
 	if node.cond_type.idx() == 0 {
@@ -721,7 +775,7 @@ fn (mut c Checker) match_exprs(mut node ast.MatchExpr, cond_type_sym ast.TypeSym
 					}
 				}
 				else {
-					key = (*expr).str()
+					key = c.get_match_case_int_key(mut expr, cond_sym) or { (*expr).str() }
 				}
 			}
 			val := if key in branch_exprs { branch_exprs[key] } else { 0 }
diff --git a/vlib/v/checker/tests/match_duplicate_branch_mixed_int_literals.out b/vlib/v/checker/tests/match_duplicate_branch_mixed_int_literals.out
new file mode 100644
index 000000000..2e7876ea9
--- /dev/null
+++ b/vlib/v/checker/tests/match_duplicate_branch_mixed_int_literals.out
@@ -0,0 +1,14 @@
+vlib/v/checker/tests/match_duplicate_branch_mixed_int_literals.vv:3:3: error: match case `10` is handled more than once
+    1 | fn parse(ch u8) ! {
+    2 |     match ch {
+    3 |         ` `, `\t`, `\n`, 10 {
+      |         ~~~~~~~~~~~~~~~~~~~
+    4 |             // consume blanks
+    5 |         }
+vlib/v/checker/tests/match_duplicate_branch_mixed_int_literals.vv:17:3: error: match case `10` is handled more than once
+   15 | fn parse_cast(ch u8) ! {
+   16 |     match ch {
+   17 |         `\n`, u8(10) {
+      |         ~~~~~~~~~~~~
+   18 |             println('line feed')
+   19 |         }
diff --git a/vlib/v/checker/tests/match_duplicate_branch_mixed_int_literals.vv b/vlib/v/checker/tests/match_duplicate_branch_mixed_int_literals.vv
new file mode 100644
index 000000000..3090c5be8
--- /dev/null
+++ b/vlib/v/checker/tests/match_duplicate_branch_mixed_int_literals.vv
@@ -0,0 +1,29 @@
+fn parse(ch u8) ! {
+	match ch {
+		` `, `\t`, `\n`, 10 {
+			// consume blanks
+		}
+		`<` {
+			println('open')
+		}
+		else {
+			return error('root invalid char')
+		}
+	}
+}
+
+fn parse_cast(ch u8) ! {
+	match ch {
+		`\n`, u8(10) {
+			println('line feed')
+		}
+		else {
+			return error('root invalid char')
+		}
+	}
+}
+
+fn main() {
+	parse(`<`)!
+	parse_cast(`\n`)!
+}
-- 
2.39.5