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/*
Portions Copyright 2019-2021 ZomboDB, LLC.
Portions Copyright 2021-2022 Technology Concepts & Design, Inc. <support@tcdi.com>

All rights reserved.

Use of this source code is governed by the MIT license that can be found in the LICENSE file.
*/
/*!

`#[pgrx]` attribute for Rust to SQL mapping support.

> Like all of the [`sql_entity_graph`][crate::pgrx_sql_entity_graph] APIs, this is considered **internal**
to the `pgrx` framework and very subject to change between versions. While you may use this, please do it with caution.

*/
use syn::parse::{Parse, ParseStream};
use syn::punctuated::Punctuated;
use syn::{parenthesized, token, Token};

/// This struct is intended to represent the contents of the `#[pgrx]` attribute when parsed.
///
/// The intended usage is to parse an `Attribute`, then use `attr.parse_args::<PgrxAttribute>()?` to
/// parse the contents of the attribute into this struct.
///
/// We use this rather than `Attribute::parse_meta` because it is not supported to parse bare paths
/// as values of a `NameValueMeta`, and we want to support that to avoid conflating SQL strings with
/// paths-as-strings. We re-use as much of the standard `parse_meta` structure types as possible though.
pub struct PgrxAttribute {
    pub args: Vec<PgrxArg>,
}

impl Parse for PgrxAttribute {
    fn parse(input: ParseStream<'_>) -> syn::Result<Self> {
        let parser = Punctuated::<PgrxArg, Token![,]>::parse_terminated;
        let punctuated = input.call(parser)?;
        let args = punctuated.into_pairs().map(|p| p.into_value()).collect::<Vec<_>>();
        Ok(Self { args })
    }
}

/// This enum is akin to `syn::Meta`, but supports a custom `NameValue` variant which allows
/// for bare paths in the value position.
pub enum PgrxArg {
    Path(syn::Path),
    List(syn::MetaList),
    NameValue(NameValueArg),
}

impl Parse for PgrxArg {
    fn parse(input: ParseStream<'_>) -> syn::Result<Self> {
        let path = input.parse::<syn::Path>()?;
        if input.peek(token::Paren) {
            let content;
            Ok(Self::List(syn::MetaList {
                path,
                paren_token: parenthesized!(content in input),
                nested: content.parse_terminated(syn::NestedMeta::parse)?,
            }))
        } else if input.peek(Token![=]) {
            Ok(Self::NameValue(NameValueArg {
                path,
                eq_token: input.parse()?,
                value: input.parse()?,
            }))
        } else {
            Ok(Self::Path(path))
        }
    }
}

/// This struct is akin to `syn::NameValueMeta`, but allows for more than just `syn::Lit` as a value.
pub struct NameValueArg {
    pub path: syn::Path,
    pub eq_token: syn::token::Eq,
    pub value: ArgValue,
}

/// This is the type of a value that can be used in the value position of a `name = value` attribute argument.
pub enum ArgValue {
    Path(syn::Path),
    Lit(syn::Lit),
}

impl Parse for ArgValue {
    fn parse(input: ParseStream<'_>) -> syn::Result<Self> {
        if input.peek(syn::Lit) {
            return Ok(Self::Lit(input.parse()?));
        }

        Ok(Self::Path(input.parse()?))
    }
}