Escaping doesn't work as expected

[joshuataylor]

Description

When using {{ '\'' }}, the following error is thrown:

called `Result::unwrap()` on an `Err` value: Error { kind: BadEscape, detail: None, name: Some("concat.txt"), lineno: 2, source: None }

(Ignore the test file, I initially thought it might be a concat issue, it's not.

Reproduction steps

    let mut env = Environment::new();
    env.add_template("escape", "{{ '\'' }}").unwrap();

Additional helpful information:

• Version of minijinja: Latest git (310a12b)
• Version of rustc: rustc 1.65.0-nightly (bc4b39c27 2022-08-29)
• Operating system and version: ArchLinux btw 5.19

What did you expect

It escaped.

It's handy to do things like this:

{% set result = run_query('select add_months(\''~ start_month ~ '-01\'::date, 11)::date') %}

Though you should use " ;).

{% set result = run_query("select add_months('"~ start_month ~ "'-01'::date, 11)::date") %}

I'm looking into this, just thought I should raise it 👍