Infinite loop in Semantic Analysis step

[paulsmith]

The following code triggers a seemingly infinite Semantic Analysis step that never completes.

const std = @import("std");

const Node = union(enum) {
    leaf: u8,
    node: ?*Node,

    pub fn format(self: Node, comptime fmt: []const u8, options: std.fmt.FormatOptions, writer: anytype) @TypeOf(writer).Error!void {
        switch (self) {
            .leaf => {
                try writer.writeAll("leaf=\"");
                try std.fmt.format(writer, "{}", .{self.leaf});
                try writer.writeAll("\"");
            },
            .node => {
                try writer.writeAll("node=[");
                if (self.node) |n| try n.format("{}", std.fmt.FormatOptions{}, writer);
                try writer.writeAll("]");
            },
        }
    }
};

pub fn main() anyerror!void {
    var leaf = Node{ .leaf = 127 };
    var node = Node{ .node = &leaf };
    var root = Node{ .node = &node };
    std.debug.print("{}\n", .{root});
}

I expect node=[node=[leaf="127"]] to be printed.

If you comment out either the call to std.fmt.format in the .leaf arm or the recursive call to Node.format in the .node arm, the code compiles.

[Vexu]

Duplicate of #4572.