Escaping Quotation Marks

[niclo]

I decided to address this in the Q&A forum as I am not sure if this is an issue or an intended design decision.

TL;DR: Escaping quotation marks in defmt::Format implementations is not supported.

Using the implementation impl defmt::Format for Key from esp-nvs as an example:

pub struct Key([u8; 16]);

impl Key {
    // ...

    /// Returns the key as a string slice, excluding null padding.
    pub fn as_str(&self) -> &str {
        let len = self.0.iter().position(|&b| b == 0).unwrap_or(self.0.len());
        unsafe { core::str::from_utf8_unchecked(&self.0[..len]) }
    }
}

impl defmt::Format for Key {
    fn format(&self, f: defmt::Formatter) {
        defmt::write!(f, "{}", self.as_str());
    }
}

The code above works as intended but however the following code

impl defmt::Format for Key {
    fn format(&self, f: defmt::Formatter) {
        defmt::write!(f, "Key(\"{}\")", self.as_str());
    }
}

Produces the error

  × failed to demangle defmt symbol `{"package":"esp-nvs","tag":"defmt_write","data":"Key(b"","disambiguator":"10210432388362800501","crate_name":"esp_nvs"}`: expected `,` or `}` at line 1 column 56
  ╰─▶ Failed to parse defmt data

Based on the error it seems that this behavior is unintended however I could be mistaken. I would appreciate any clarity on this matter, thank you.