[lib]
name = "displaydoc"
path = "src/lib.rs"
proc-macro = true

build = false

        let literals = attrs
            .iter()
            .filter(|attr| attr.path().is_ident("doc"))
            .map(|attr| match &attr.meta {
                Meta::NameValue(syn::MetaNameValue {
                    value:
                        syn::Expr::Lit(syn::ExprLit {
                            lit: syn::Lit::Str(lit),
                            ..
                        }),
                    ..
                }) => lit,
                _ => unimplemented!(),
            });

        }.unwrap_or_else(|| {
            panic!("Paragraph breaks in multi-line doc comments are disabled by default by displaydoc. Please consider using block doc comments (/** */) or adding the #[ignore_extra_doc_attributes] attribute to your type next to the derive");
        }).join(" ");

#[cfg(feature = "std")]
fn specialization() -> TokenStream {
    quote! {
        trait DisplayToDisplayDoc {
            fn __displaydoc_display(&self) -> Self;
        }

        impl<T: ::core::fmt::Display> DisplayToDisplayDoc for &T {
            fn __displaydoc_display(&self) -> Self {
                self
            }
        }

        // If the `std` feature gets enabled we want to ensure that any crate
        // using displaydoc can still reference the std crate, which is already
        // being compiled in by whoever enabled the `std` feature in
        // `displaydoc`, even if the crates using displaydoc are no_std.
        extern crate std;

        trait PathToDisplayDoc {
            fn __displaydoc_display(&self) -> std::path::Display<'_>;
        }

        impl PathToDisplayDoc for std::path::Path {
            fn __displaydoc_display(&self) -> std::path::Display<'_> {
                self.display()
            }
        }

        impl PathToDisplayDoc for std::path::PathBuf {
            fn __displaydoc_display(&self) -> std::path::Display<'_> {
                self.display()
            }
        }
    }
}

#[cfg(not(feature = "std"))]
fn specialization() -> TokenStream {
    quote! {}
}

/// Hygienically add `where _: Display` to the set of [TypeParamBound]s for `ident`, creating such
/// a set if necessary.
fn ensure_display_in_where_clause_for_type(where_clause: &mut WhereClause, ident: Ident) {
    for pred_ty in where_clause
        .predicates
        .iter_mut()
        // Find the `where` predicate constraining the current type param, if it exists.
        .flat_map(|predicate| match predicate {
            WherePredicate::Type(pred_ty) => Some(pred_ty),
            // We're looking through type constraints, not lifetime constraints.
            _ => None,
        })
    {
        // Do a complicated destructuring in order to check if the type being constrained in this
        // `where` clause is the type we're looking for, so we can use the mutable reference to
        // `pred_ty` if so.
        let matches_desired_type = matches!(
            &pred_ty.bounded_ty,
            Type::Path(TypePath { path, .. }) if Some(&ident) == path.get_ident());
        if matches_desired_type {
            add_display_constraint_to_type_predicate(pred_ty);
            return;
        }
    }

    // If there is no `where` predicate for the current type param, we will construct one.
    let mut new_type_predicate = new_empty_where_type_predicate(ident);
    add_display_constraint_to_type_predicate(&mut new_type_predicate);
    append_where_clause_type_predicate(where_clause, new_type_predicate);
}

/// For all declared type parameters, add a [core::fmt::Display] constraint, unless the type
/// parameter already has any type constraint.
fn ensure_where_clause_has_display_for_all_unconstrained_members(
    where_clause: &mut WhereClause,
    type_params: &[&TypeParam],
) {
    let param_constraint_mapping = extract_trait_constraints_from_source(where_clause, type_params);

    for (ident, known_bounds) in param_constraint_mapping.into_iter() {
        // If the type parameter has any constraints already, we don't want to touch it, to avoid
        // breaking use cases where a type parameter only needs to impl `Debug`, for example.
        if known_bounds.is_empty() {
            ensure_display_in_where_clause_for_type(where_clause, ident);
        }
    }
}

/// Generate a `where` clause that ensures all generic type parameters `impl`
/// [core::fmt::Display] unless already constrained.
///
/// This approach allows struct/enum definitions deriving [crate::Display] to avoid hardcoding
/// a [core::fmt::Display] constraint into every type parameter.
///
/// If the type parameter isn't already constrained, we add a `where _: Display` clause to our
/// display implementation to expect to be able to format every enum case or struct member.
///
/// In fact, we would preferably only require `where _: Display` or `where _: Debug` where the
/// format string actually requires it. However, while [`std::fmt` defines a formal syntax for
/// `format!()`][format syntax], it *doesn't* expose the actual logic to parse the format string,
/// which appears to live in [`rustc_parse_format`]. While we use the [`syn`] crate to parse rust
/// syntax, it also doesn't currently provide any method to introspect a `format!()` string. It
/// would be nice to contribute this upstream in [`syn`].
///
/// [format syntax]: std::fmt#syntax
/// [`rustc_parse_format`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse_format/index.html
fn generate_where_clause(generics: &Generics, where_clause: Option<&WhereClause>) -> WhereClause {
    let mut where_clause = where_clause.cloned().unwrap_or_else(new_empty_where_clause);
    let type_params: Vec<&TypeParam> = generics.type_params().collect();
    ensure_where_clause_has_display_for_all_unconstrained_members(&mut where_clause, &type_params);
    where_clause
}

    pub(crate) fn expand_shorthand(&mut self) {
        let span = self.fmt.span();
        let fmt = self.fmt.value();
        let mut read = fmt.as_str();
        let mut out = String::new();
        let mut args = TokenStream::new();

        while let Some(brace) = read.find('{') {
            out += &read[..=brace];
            read = &read[brace + 1..];

            // skip cases where we find a {{
            if read.starts_with('{') {
                out.push('{');
                read = &read[1..];
                continue;
            }

            let next = peek_next!(read);

            let var = match next {
                '0'..='9' => take_int(&mut read),
                'a'..='z' | 'A'..='Z' | '_' => take_ident(&mut read),
                _ => return,
            };

            let ident = Ident::new(&var, span);

            let next = peek_next!(read);

            let arg = if cfg!(feature = "std") && next == '}' {
                quote_spanned!(span=> , #ident.__displaydoc_display())
            } else {
                quote_spanned!(span=> , #ident)
            };

            args.extend(arg);
        }

        out += read;
        self.fmt = LitStr::new(&out, self.fmt.span());
        self.args = args;
    }

#[proc_macro_derive(
    Display,
    attributes(ignore_extra_doc_attributes, prefix_enum_doc_attributes, displaydoc)
)]
pub fn derive_error(input: TokenStream) -> TokenStream {
    let input = parse_macro_input!(input as DeriveInput);
    expand::derive(&input)
        .unwrap_or_else(|err| err.to_compile_error())
        .into()
}