fmt: proper single line check for ConcatExpr (#9121)

vlib/v/fmt/fmt.v

@@ -1070,6 +1070,13 @@ fn expr_is_single_line(expr ast.Expr) bool {
 				return expr_is_single_line(expr.exprs[0])
 			}
 		}
+		ast.ConcatExpr {
+			for e in expr.vals {
+				if !expr_is_single_line(e) {
+					return false
+				}
+			}
+		}
 		else {}
 	}
 	return true
@@ -1698,6 +1705,13 @@ pub fn (mut f Fmt) wrap_infix(start_pos int, start_len int, ignore_paren bool) {
 	}
 }
 
+fn branch_is_single_line(b ast.IfBranch) bool {
+	if b.stmts.len == 1 && b.comments.len == 0 && stmt_is_single_line(b.stmts[0]) {
+		return true
+	}
+	return false
+}
+
 pub fn (mut f Fmt) if_expr(node ast.IfExpr) {
 	dollar := if node.is_comptime { '$' } else { '' }
 	mut is_ternary := node.branches.len == 2 && node.has_else
@@ -1769,13 +1783,6 @@ pub fn (mut f Fmt) if_expr(node ast.IfExpr) {
 	}
 }
 
-fn branch_is_single_line(b ast.IfBranch) bool {
-	if b.stmts.len == 1 && b.comments.len == 0 && stmt_is_single_line(b.stmts[0]) {
-		return true
-	}
-	return false
-}
-
 pub fn (mut f Fmt) at_expr(node ast.AtExpr) {
 	f.write(node.name)
 }

vlib/v/fmt/tests/expressions_expected.vv

@@ -80,3 +80,24 @@ fn (mut p Parser) name_expr() {
 fn set_nr_muls(t table.Type, nr_muls int) table.Type {
 	return int(t) & 0xff00ffff | (nr_muls << 16)
 }
+
+// Test what exprs are treated as multiline. The ternary if only functions as a wrapper.
+// When one expr in a branch doesn't fit a single line, the whole if will be unwrapped.
+fn multiline_exprs() {
+	// StructInit with at least one field
+	_ := if true {
+		Foo{}
+	} else {
+		Foo{
+			val: 123
+		}
+	}
+	// ConcatExpr with a multiline child expr
+	_, _ := if true {
+		1, Foo{
+			val: 123
+		}
+	} else {
+		2, Foo{}
+	}
+}

vlib/v/fmt/tests/expressions_input.vv

@@ -91,3 +91,12 @@ fn set_nr_muls(t table.Type, nr_muls int) table.Type {
 	return int(t) &
 		0xff00ffff | (nr_muls << 16)
 }
+
+// Test what exprs are treated as multiline. The ternary if only functions as a wrapper.
+// When one expr in a branch doesn't fit a single line, the whole if will be unwrapped.
+fn multiline_exprs() {
+	// StructInit with at least one field
+	_ := if true { Foo{} } else { Foo{ val: 123} }
+	// ConcatExpr with a multiline child expr
+	_, _ := if true { 1, Foo{val: 123} } else { 2, Foo{} }
+}