1// Copyright (c) 2024 Jonas Schäfer <jonas@zombofant.net>
  2//
  3// This Source Code Form is subject to the terms of the Mozilla Public
  4// License, v. 2.0. If a copy of the MPL was not distributed with this
  5// file, You can obtain one at http://mozilla.org/MPL/2.0/.
  6
  7//! Infrastructure for contextual error messages
  8
  9use std::fmt;
 10
 11use syn::*;
 12
 13/// Reference to a compound field's parent
 14///
 15/// This reference can be converted to a hopefully-useful human-readable
 16/// string via [`std::fmt::Display`].
 17#[derive(Clone, Debug)]
 18pub(super) enum ParentRef {
 19    /// The parent is addressable by a path, e.g. a struct type or enum
 20    /// variant.
 21    Named(Path),
 22}
 23
 24impl From<Path> for ParentRef {
 25    fn from(other: Path) -> Self {
 26        Self::Named(other)
 27    }
 28}
 29
 30impl From<&Path> for ParentRef {
 31    fn from(other: &Path) -> Self {
 32        Self::Named(other.clone())
 33    }
 34}
 35
 36impl fmt::Display for ParentRef {
 37    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 38        match self {
 39            Self::Named(name) => {
 40                let mut first = true;
 41                for segment in name.segments.iter() {
 42                    if !first || name.leading_colon.is_some() {
 43                        write!(f, "::")?;
 44                    }
 45                    first = false;
 46                    write!(f, "{}", segment.ident)?;
 47                }
 48                write!(f, " element")
 49            }
 50        }
 51    }
 52}
 53
 54/// Ephemeral struct to create a nice human-readable representation of
 55/// [`syn::Member`].
 56///
 57/// It implements [`std::fmt::Display`] for that purpose and is otherwise of
 58/// little use.
 59#[repr(transparent)]
 60struct FieldName<'x>(&'x Member);
 61
 62impl fmt::Display for FieldName<'_> {
 63    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 64        match self.0 {
 65            Member::Named(v) => write!(f, "field '{}'", v),
 66            Member::Unnamed(v) => write!(f, "unnamed field {}", v.index),
 67        }
 68    }
 69}
 70
 71/// Create a string error message for a missing attribute.
 72///
 73/// `parent_name` should point at the compound which is being parsed and
 74/// `field` should be the field to which the attribute belongs.
 75pub(super) fn on_missing_attribute(parent_name: &ParentRef, field: &Member) -> String {
 76    format!(
 77        "Required attribute {} on {} missing.",
 78        FieldName(field),
 79        parent_name
 80    )
 81}
 82
 83/// Create a string error message for a missing child element.
 84///
 85/// `parent_name` should point at the compound which is being parsed and
 86/// `field` should be the field to which the child belongs.
 87pub(super) fn on_missing_child(parent_name: &ParentRef, field: &Member) -> String {
 88    format!("Missing child {} in {}.", FieldName(&field), parent_name)
 89}
 90
 91/// Create a string error message for a duplicate child element.
 92///
 93/// `parent_name` should point at the compound which is being parsed and
 94/// `field` should be the field to which the child belongs.
 95pub(super) fn on_duplicate_child(parent_name: &ParentRef, field: &Member) -> String {
 96    format!(
 97        "{} must not have more than one child in {}.",
 98        parent_name,
 99        FieldName(&field)
100    )
101}