checker: error on ternary if type mismatch

vlib/builtin/map.v

@@ -157,7 +157,7 @@ fn (d mut DenseArray) zeros_to_end() {
 	}
 	d.deletes = 0
 	d.size = count
-	d.cap = if count < 8 { 8 } else { count }
+	d.cap = if count < 8 { u32(8) } else { count }
 	d.data = &KeyValue(C.realloc(d.data, sizeof(KeyValue) * d.cap))
 }
 

vlib/v/checker/checker.v

@@ -1827,6 +1827,8 @@ pub fn (mut c Checker) if_expr(node mut ast.IfExpr) table.Type {
 		node.is_expr = true
 	}
 	node.typ = table.void_type
+	mut first_typ := 0
+	is_ternary := node.is_expr && node.branches.len >= 2 && node.has_else
 	for i, branch in node.branches {
 		if branch.cond is ast.ParExpr {
 			c.error('unnecessary `()` in an if condition. use `if expr {` instead of `if (expr) {`.',
@@ -1840,6 +1842,13 @@ pub fn (mut c Checker) if_expr(node mut ast.IfExpr) table.Type {
 				c.error('non-bool (`$typ_sym.name`) used as if condition', node.pos)
 			}
 		}
+		if is_ternary && i < node.branches.len - 1 && branch.stmts.len > 0 {
+			last_stmt := branch.stmts[branch.stmts.len - 1]
+			if last_stmt is ast.ExprStmt {
+				last_expr := last_stmt as ast.ExprStmt
+				first_typ = c.expr(last_expr.expr)
+			}
+		}
 		c.stmts(branch.stmts)
 	}
 	if node.has_else && node.is_expr {
@@ -1850,6 +1859,9 @@ pub fn (mut c Checker) if_expr(node mut ast.IfExpr) table.Type {
 					// type_sym := p.table.get_type_symbol(it.typ)
 					// p.warn('if expr ret $type_sym.name')
 					t := c.expr(it.expr)
+					if is_ternary && t != first_typ {
+						c.error('mismatched types `${c.table.type_to_str(first_typ)}` and `${c.table.type_to_str(t)}`', node.pos)
+					}					
 					node.typ = t
 					return t
 				}

vlib/v/checker/tests/ternary_mismatch.out

@@ -0,0 +1,6 @@
+vlib/v/checker/tests/ternary_mismatch.v:2:7: error: mismatched types `string` and `int` 
+    1| fn main() {
+    2|     s := if true { '12' } else { 12 }
+                ~~
+    3|     println(s)
+    4| }

vlib/v/checker/tests/ternary_mismatch.vv

@@ -0,0 +1,4 @@
+fn main() {
+	s := if true { '12' } else { 12 }
+	println(s)
+}