conf.rs

//! Read configurations files.

#![allow(clippy::module_name_repetitions)]

use serde::de::{Deserializer, IgnoredAny, IntoDeserializer, MapAccess, Visitor};
use serde::Deserialize;
use std::error::Error;
use std::path::{Path, PathBuf};
use std::str::FromStr;
use std::{cmp, env, fmt, fs, io, iter};

#[rustfmt::skip]
const DEFAULT_DOC_VALID_IDENTS: &[&str] = &[
    "KiB", "MiB", "GiB", "TiB", "PiB", "EiB",
    "DirectX",
    "ECMAScript",
    "GPLv2", "GPLv3",
    "GitHub", "GitLab",
    "IPv4", "IPv6",
    "ClojureScript", "CoffeeScript", "JavaScript", "PureScript", "TypeScript",
    "NaN", "NaNs",
    "OAuth", "GraphQL",
    "OCaml",
    "OpenGL", "OpenMP", "OpenSSH", "OpenSSL", "OpenStreetMap", "OpenDNS",
    "WebGL",
    "TensorFlow",
    "TrueType",
    "iOS", "macOS", "FreeBSD",
    "TeX", "LaTeX", "BibTeX", "BibLaTeX",
    "MinGW",
    "CamelCase",
];
const DEFAULT_DISALLOWED_NAMES: &[&str] = &["foo", "baz", "quux"];

/// Holds information used by `MISSING_ENFORCED_IMPORT_RENAMES` lint.
#[derive(Clone, Debug, Deserialize)]
pub struct Rename {
    pub path: String,
    pub rename: String,
}

#[derive(Clone, Debug, Deserialize)]
#[serde(untagged)]
pub enum DisallowedPath {
    Simple(String),
    WithReason { path: String, reason: Option<String> },
}

impl DisallowedPath {
    pub fn path(&self) -> &str {
        let (Self::Simple(path) | Self::WithReason { path, .. }) = self;

        path
    }

    pub fn reason(&self) -> Option<String> {
        match self {
            Self::WithReason {
                reason: Some(reason), ..
            } => Some(format!("{reason} (from clippy.toml)")),
            _ => None,
        }
    }
}

/// Conf with parse errors
#[derive(Default)]
pub struct TryConf {
    pub conf: Conf,
    pub errors: Vec<Box<dyn Error>>,
    pub warnings: Vec<Box<dyn Error>>,
}

impl TryConf {
    fn from_error(error: impl Error + 'static) -> Self {
        Self {
            conf: Conf::default(),
            errors: vec![Box::new(error)],
            warnings: vec![],
        }
    }
}

#[derive(Debug)]
struct ConfError(String);

impl fmt::Display for ConfError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        <String as fmt::Display>::fmt(&self.0, f)
    }
}

impl Error for ConfError {}

fn conf_error(s: impl Into<String>) -> Box<dyn Error> {
    Box::new(ConfError(s.into()))
}

macro_rules! define_Conf {
    ($(
        $(#[doc = $doc:literal])+
        $(#[conf_deprecated($dep:literal, $new_conf:ident)])?
        ($name:ident: $ty:ty = $default:expr),
    )*) => {
        /// Clippy lint configuration
        pub struct Conf {
            $($(#[doc = $doc])+ pub $name: $ty,)*
        }

        mod defaults {
            $(pub fn $name() -> $ty { $default })*
        }

        impl Default for Conf {
            fn default() -> Self {
                Self { $($name: defaults::$name(),)* }
            }
        }

        impl<'de> Deserialize<'de> for TryConf {
            fn deserialize<D>(deserializer: D) -> Result<Self, D::Error> where D: Deserializer<'de> {
                deserializer.deserialize_map(ConfVisitor)
            }
        }

        #[derive(Deserialize)]
        #[serde(field_identifier, rename_all = "kebab-case")]
        #[allow(non_camel_case_types)]
        enum Field { $($name,)* third_party, }

        struct ConfVisitor;

        impl<'de> Visitor<'de> for ConfVisitor {
            type Value = TryConf;

            fn expecting(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
                formatter.write_str("Conf")
            }

            fn visit_map<V>(self, mut map: V) -> Result<Self::Value, V::Error> where V: MapAccess<'de> {
                let mut errors = Vec::new();
                let mut warnings = Vec::new();
                $(let mut $name = None;)*
                // could get `Field` here directly, but get `str` first for diagnostics
                while let Some(name) = map.next_key::<&str>()? {
                    match Field::deserialize(name.into_deserializer())? {
                        $(Field::$name => {
                            $(warnings.push(conf_error(format!("deprecated field `{}`. {}", name, $dep)));)?
                            match map.next_value() {
                                Err(e) => errors.push(conf_error(e.to_string())),
                                Ok(value) => match $name {
                                    Some(_) => errors.push(conf_error(format!("duplicate field `{}`", name))),
                                    None => {
                                        $name = Some(value);
                                        // $new_conf is the same as one of the defined `$name`s, so
                                        // this variable is defined in line 2 of this function.
                                        $(match $new_conf {
                                            Some(_) => errors.push(conf_error(concat!(
                                                "duplicate field `", stringify!($new_conf),
                                                "` (provided as `", stringify!($name), "`)"
                                            ))),
                                            None => $new_conf = $name.clone(),
                                        })?
                                    },
                                }
                            }
                        })*
                        // white-listed; ignore
                        Field::third_party => drop(map.next_value::<IgnoredAny>())
                    }
                }
                let conf = Conf { $($name: $name.unwrap_or_else(defaults::$name),)* };
                Ok(TryConf { conf, errors, warnings })
            }
        }

        #[cfg(feature = "internal")]
        pub mod metadata {
            use crate::utils::internal_lints::metadata_collector::ClippyConfiguration;

            macro_rules! wrap_option {
                () => (None);
                ($x:literal) => (Some($x));
            }

            pub(crate) fn get_configuration_metadata() -> Vec<ClippyConfiguration> {
                vec![
                    $(
                        {
                            let deprecation_reason = wrap_option!($($dep)?);

                            ClippyConfiguration::new(
                                stringify!($name),
                                stringify!($ty),
                                format!("{:?}", super::defaults::$name()),
                                concat!($($doc, '\n',)*),
                                deprecation_reason,
                            )
                        },
                    )+
                ]
            }
        }
    };
}

define_Conf! {
    /// Lint: ARITHMETIC_SIDE_EFFECTS.
    ///
    /// Suppress checking of the passed type names in all types of operations.
    ///
    /// If a specific operation is desired, consider using `arithmetic_side_effects_allowed_binary` or `arithmetic_side_effects_allowed_unary` instead.
    ///
    /// #### Example
    ///
    /// ```toml
    /// arithmetic-side-effects-allowed = ["SomeType", "AnotherType"]
    /// ```
    ///
    /// #### Noteworthy
    ///
    /// A type, say `SomeType`, listed in this configuration has the same behavior of
    /// `["SomeType" , "*"], ["*", "SomeType"]` in `arithmetic_side_effects_allowed_binary`.
    (arithmetic_side_effects_allowed: rustc_data_structures::fx::FxHashSet<String> = <_>::default()),
    /// Lint: ARITHMETIC_SIDE_EFFECTS.
    ///
    /// Suppress checking of the passed type pair names in binary operations like addition or
    /// multiplication.
    ///
    /// Supports the "*" wildcard to indicate that a certain type won't trigger the lint regardless
    /// of the involved counterpart. For example, `["SomeType", "*"]` or `["*", "AnotherType"]`.
    ///
    /// Pairs are asymmetric, which means that `["SomeType", "AnotherType"]` is not the same as
    /// `["AnotherType", "SomeType"]`.
    ///
    /// #### Example
    ///
    /// ```toml
    /// arithmetic-side-effects-allowed-binary = [["SomeType" , "f32"], ["AnotherType", "*"]]
    /// ```
    (arithmetic_side_effects_allowed_binary: Vec<[String; 2]> = <_>::default()),
    /// Lint: ARITHMETIC_SIDE_EFFECTS.
    ///
    /// Suppress checking of the passed type names in unary operations like "negation" (`-`).
    ///
    /// #### Example
    ///
    /// ```toml
    /// arithmetic-side-effects-allowed-unary = ["SomeType", "AnotherType"]
    /// ```
    (arithmetic_side_effects_allowed_unary: rustc_data_structures::fx::FxHashSet<String> = <_>::default()),
    /// Lint: ENUM_VARIANT_NAMES, LARGE_TYPES_PASSED_BY_VALUE, TRIVIALLY_COPY_PASS_BY_REF, UNNECESSARY_WRAPS, UNUSED_SELF, UPPER_CASE_ACRONYMS, WRONG_SELF_CONVENTION, BOX_COLLECTION, REDUNDANT_ALLOCATION, RC_BUFFER, VEC_BOX, OPTION_OPTION, LINKEDLIST, RC_MUTEX, UNNECESSARY_BOX_RETURNS.
    ///
    /// Suppress lints whenever the suggested change would cause breakage for other crates.
    (avoid_breaking_exported_api: bool = true),
    /// Lint: MANUAL_SPLIT_ONCE, MANUAL_STR_REPEAT, CLONED_INSTEAD_OF_COPIED, REDUNDANT_FIELD_NAMES, REDUNDANT_STATIC_LIFETIMES, FILTER_MAP_NEXT, CHECKED_CONVERSIONS, MANUAL_RANGE_CONTAINS, USE_SELF, MEM_REPLACE_WITH_DEFAULT, MANUAL_NON_EXHAUSTIVE, OPTION_AS_REF_DEREF, MAP_UNWRAP_OR, MATCH_LIKE_MATCHES_MACRO, MANUAL_STRIP, MISSING_CONST_FOR_FN, UNNESTED_OR_PATTERNS, FROM_OVER_INTO, PTR_AS_PTR, IF_THEN_SOME_ELSE_NONE, APPROX_CONSTANT, DEPRECATED_CFG_ATTR, INDEX_REFUTABLE_SLICE, MAP_CLONE, BORROW_AS_PTR, MANUAL_BITS, ERR_EXPECT, CAST_ABS_TO_UNSIGNED, UNINLINED_FORMAT_ARGS, MANUAL_CLAMP, MANUAL_LET_ELSE, UNCHECKED_DURATION_SUBTRACTION, COLLAPSIBLE_STR_REPLACE, SEEK_FROM_CURRENT, SEEK_REWIND, UNNECESSARY_LAZY_EVALUATIONS, TRANSMUTE_PTR_TO_REF, ALMOST_COMPLETE_RANGE, NEEDLESS_BORROW, DERIVABLE_IMPLS, MANUAL_IS_ASCII_CHECK, MANUAL_REM_EUCLID, MANUAL_RETAIN.
    ///
    /// The minimum rust version that the project supports
    (msrv: Option<String> = None),
    /// DEPRECATED LINT: BLACKLISTED_NAME.
    ///
    /// Use the Disallowed Names lint instead
    #[conf_deprecated("Please use `disallowed-names` instead", disallowed_names)]
    (blacklisted_names: Vec<String> = Vec::new()),
    /// Lint: COGNITIVE_COMPLEXITY.
    ///
    /// The maximum cognitive complexity a function can have
    (cognitive_complexity_threshold: u64 = 25),
    /// DEPRECATED LINT: CYCLOMATIC_COMPLEXITY.
    ///
    /// Use the Cognitive Complexity lint instead.
    #[conf_deprecated("Please use `cognitive-complexity-threshold` instead", cognitive_complexity_threshold)]
    (cyclomatic_complexity_threshold: u64 = 25),
    /// Lint: DISALLOWED_NAMES.
    ///
    /// The list of disallowed names to lint about. NB: `bar` is not here since it has legitimate uses. The value
    /// `".."` can be used as part of the list to indicate, that the configured values should be appended to the
    /// default configuration of Clippy. By default any configuration will replace the default value.
    (disallowed_names: Vec<String> = super::DEFAULT_DISALLOWED_NAMES.iter().map(ToString::to_string).collect()),
    /// Lint: DOC_MARKDOWN.
    ///
    /// The list of words this lint should not consider as identifiers needing ticks. The value
    /// `".."` can be used as part of the list to indicate, that the configured values should be appended to the
    /// default configuration of Clippy. By default any configuraction will replace the default value. For example:
    /// * `doc-valid-idents = ["ClipPy"]` would replace the default list with `["ClipPy"]`.
    /// * `doc-valid-idents = ["ClipPy", ".."]` would append `ClipPy` to the default list.
    ///
    /// Default list:
    (doc_valid_idents: Vec<String> = super::DEFAULT_DOC_VALID_IDENTS.iter().map(ToString::to_string).collect()),
    /// Lint: TOO_MANY_ARGUMENTS.
    ///
    /// The maximum number of argument a function or method can have
    (too_many_arguments_threshold: u64 = 7),
    /// Lint: TYPE_COMPLEXITY.
    ///
    /// The maximum complexity a type can have
    (type_complexity_threshold: u64 = 250),
    /// Lint: MANY_SINGLE_CHAR_NAMES.
    ///
    /// The maximum number of single char bindings a scope may have
    (single_char_binding_names_threshold: u64 = 4),
    /// Lint: BOXED_LOCAL, USELESS_VEC.
    ///
    /// The maximum size of objects (in bytes) that will be linted. Larger objects are ok on the heap
    (too_large_for_stack: u64 = 200),
    /// Lint: ENUM_VARIANT_NAMES.
    ///
    /// The minimum number of enum variants for the lints about variant names to trigger
    (enum_variant_name_threshold: u64 = 3),
    /// Lint: LARGE_ENUM_VARIANT.
    ///
    /// The maximum size of an enum's variant to avoid box suggestion
    (enum_variant_size_threshold: u64 = 200),
    /// Lint: VERBOSE_BIT_MASK.
    ///
    /// The maximum allowed size of a bit mask before suggesting to use 'trailing_zeros'
    (verbose_bit_mask_threshold: u64 = 1),
    /// Lint: DECIMAL_LITERAL_REPRESENTATION.
    ///
    /// The lower bound for linting decimal literals
    (literal_representation_threshold: u64 = 16384),
    /// Lint: TRIVIALLY_COPY_PASS_BY_REF.
    ///
    /// The maximum size (in bytes) to consider a `Copy` type for passing by value instead of by reference.
    (trivial_copy_size_limit: Option<u64> = None),
    /// Lint: LARGE_TYPES_PASSED_BY_VALUE.
    ///
    /// The minimum size (in bytes) to consider a type for passing by reference instead of by value.
    (pass_by_value_size_limit: u64 = 256),
    /// Lint: TOO_MANY_LINES.
    ///
    /// The maximum number of lines a function or method can have
    (too_many_lines_threshold: u64 = 100),
    /// Lint: LARGE_STACK_ARRAYS, LARGE_CONST_ARRAYS.
    ///
    /// The maximum allowed size for arrays on the stack
    (array_size_threshold: u64 = 512_000),
    /// Lint: VEC_BOX.
    ///
    /// The size of the boxed type in bytes, where boxing in a `Vec` is allowed
    (vec_box_size_threshold: u64 = 4096),
    /// Lint: TYPE_REPETITION_IN_BOUNDS.
    ///
    /// The maximum number of bounds a trait can have to be linted
    (max_trait_bounds: u64 = 3),
    /// Lint: STRUCT_EXCESSIVE_BOOLS.
    ///
    /// The maximum number of bool fields a struct can have
    (max_struct_bools: u64 = 3),
    /// Lint: FN_PARAMS_EXCESSIVE_BOOLS.
    ///
    /// The maximum number of bool parameters a function can have
    (max_fn_params_bools: u64 = 3),
    /// Lint: WILDCARD_IMPORTS.
    ///
    /// Whether to allow certain wildcard imports (prelude, super in tests).
    (warn_on_all_wildcard_imports: bool = false),
    /// Lint: DISALLOWED_MACROS.
    ///
    /// The list of disallowed macros, written as fully qualified paths.
    (disallowed_macros: Vec<crate::utils::conf::DisallowedPath> = Vec::new()),
    /// Lint: DISALLOWED_METHODS.
    ///
    /// The list of disallowed methods, written as fully qualified paths.
    (disallowed_methods: Vec<crate::utils::conf::DisallowedPath> = Vec::new()),
    /// Lint: DISALLOWED_TYPES.
    ///
    /// The list of disallowed types, written as fully qualified paths.
    (disallowed_types: Vec<crate::utils::conf::DisallowedPath> = Vec::new()),
    /// Lint: UNREADABLE_LITERAL.
    ///
    /// Should the fraction of a decimal be linted to include separators.
    (unreadable_literal_lint_fractions: bool = true),
    /// Lint: UPPER_CASE_ACRONYMS.
    ///
    /// Enables verbose mode. Triggers if there is more than one uppercase char next to each other
    (upper_case_acronyms_aggressive: bool = false),
    /// Lint: MANUAL_LET_ELSE.
    ///
    /// Whether the matches should be considered by the lint, and whether there should
    /// be filtering for common types.
    (matches_for_let_else: crate::manual_let_else::MatchLintBehaviour =
        crate::manual_let_else::MatchLintBehaviour::WellKnownTypes),
    /// Lint: _CARGO_COMMON_METADATA.
    ///
    /// For internal testing only, ignores the current `publish` settings in the Cargo manifest.
    (cargo_ignore_publish: bool = false),
    /// Lint: NONSTANDARD_MACRO_BRACES.
    ///
    /// Enforce the named macros always use the braces specified.
    ///
    /// A `MacroMatcher` can be added like so `{ name = "macro_name", brace = "(" }`. If the macro
    /// is could be used with a full path two `MacroMatcher`s have to be added one with the full path
    /// `crate_name::macro_name` and one with just the macro name.
    (standard_macro_braces: Vec<crate::nonstandard_macro_braces::MacroMatcher> = Vec::new()),
    /// Lint: MISSING_ENFORCED_IMPORT_RENAMES.
    ///
    /// The list of imports to always rename, a fully qualified path followed by the rename.
    (enforced_import_renames: Vec<crate::utils::conf::Rename> = Vec::new()),
    /// Lint: DISALLOWED_SCRIPT_IDENTS.
    ///
    /// The list of unicode scripts allowed to be used in the scope.
    (allowed_scripts: Vec<String> = vec!["Latin".to_string()]),
    /// Lint: NON_SEND_FIELDS_IN_SEND_TY.
    ///
    /// Whether to apply the raw pointer heuristic to determine if a type is `Send`.
    (enable_raw_pointer_heuristic_for_send: bool = true),
    /// Lint: INDEX_REFUTABLE_SLICE.
    ///
    /// When Clippy suggests using a slice pattern, this is the maximum number of elements allowed in
    /// the slice pattern that is suggested. If more elements would be necessary, the lint is suppressed.
    /// For example, `[_, _, _, e, ..]` is a slice pattern with 4 elements.
    (max_suggested_slice_pattern_length: u64 = 3),
    /// Lint: AWAIT_HOLDING_INVALID_TYPE.
    (await_holding_invalid_types: Vec<crate::utils::conf::DisallowedPath> = Vec::new()),
    /// Lint: LARGE_INCLUDE_FILE.
    ///
    /// The maximum size of a file included via `include_bytes!()` or `include_str!()`, in bytes
    (max_include_file_size: u64 = 1_000_000),
    /// Lint: EXPECT_USED.
    ///
    /// Whether `expect` should be allowed in test functions or `#[cfg(test)]`
    (allow_expect_in_tests: bool = false),
    /// Lint: UNWRAP_USED.
    ///
    /// Whether `unwrap` should be allowed in test functions or `#[cfg(test)]`
    (allow_unwrap_in_tests: bool = false),
    /// Lint: DBG_MACRO.
    ///
    /// Whether `dbg!` should be allowed in test functions or `#[cfg(test)]`
    (allow_dbg_in_tests: bool = false),
    /// Lint: PRINT_STDOUT, PRINT_STDERR.
    ///
    /// Whether print macros (ex. `println!`) should be allowed in test functions or `#[cfg(test)]`
    (allow_print_in_tests: bool = false),
    /// Lint: RESULT_LARGE_ERR.
    ///
    /// The maximum size of the `Err`-variant in a `Result` returned from a function
    (large_error_threshold: u64 = 128),
    /// Lint: MUTABLE_KEY_TYPE, IFS_SAME_COND.
    ///
    /// A list of paths to types that should be treated like `Arc`, i.e. ignored but
    /// for the generic parameters for determining interior mutability
    (ignore_interior_mutability: Vec<String> = Vec::from(["bytes::Bytes".into()])),
    /// Lint: UNINLINED_FORMAT_ARGS.
    ///
    /// Whether to allow mixed uninlined format args, e.g. `format!("{} {}", a, foo.bar)`
    (allow_mixed_uninlined_format_args: bool = true),
    /// Lint: INDEXING_SLICING.
    ///
    /// Whether to suppress a restriction lint in constant code. In same
    /// cases the restructured operation might not be unavoidable, as the
    /// suggested counterparts are unavailable in constant code. This
    /// configuration will cause restriction lints to trigger even
    /// if no suggestion can be made.
    (suppress_restriction_lint_in_const: bool = false),
    /// Lint: MISSING_DOCS_IN_PRIVATE_ITEMS.
    ///
    /// Whether to **only** check for missing documentation in items visible within the current
    /// crate. For example, `pub(crate)` items.
    (missing_docs_in_crate_items: bool = false),
    /// Lint: LARGE_FUTURES.
    ///
    /// The maximum byte size a `Future` can have, before it triggers the `clippy::large_futures` lint
    (future_size_threshold: u64 = 16 * 1024),
}

/// Search for the configuration file.
///
/// # Errors
///
/// Returns any unexpected filesystem error encountered when searching for the config file
pub fn lookup_conf_file() -> io::Result<Option<PathBuf>> {
    /// Possible filename to search for.
    const CONFIG_FILE_NAMES: [&str; 2] = [".clippy.toml", "clippy.toml"];

    // Start looking for a config file in CLIPPY_CONF_DIR, or failing that, CARGO_MANIFEST_DIR.
    // If neither of those exist, use ".".
    let mut current = env::var_os("CLIPPY_CONF_DIR")
        .or_else(|| env::var_os("CARGO_MANIFEST_DIR"))
        .map_or_else(|| PathBuf::from("."), PathBuf::from);

    let mut found_config: Option<PathBuf> = None;

    loop {
        for config_file_name in &CONFIG_FILE_NAMES {
            if let Ok(config_file) = current.join(config_file_name).canonicalize() {
                match fs::metadata(&config_file) {
                    Err(e) if e.kind() == io::ErrorKind::NotFound => {},
                    Err(e) => return Err(e),
                    Ok(md) if md.is_dir() => {},
                    Ok(_) => {
                        // warn if we happen to find two config files #8323
                        if let Some(ref found_config_) = found_config {
                            eprintln!(
                                "Using config file `{}`\nWarning: `{}` will be ignored.",
                                found_config_.display(),
                                config_file.display(),
                            );
                        } else {
                            found_config = Some(config_file);
                        }
                    },
                }
            }
        }

        if found_config.is_some() {
            return Ok(found_config);
        }

        // If the current directory has no parent, we're done searching.
        if !current.pop() {
            return Ok(None);
        }
    }
}

/// Read the `toml` configuration file.
///
/// In case of error, the function tries to continue as much as possible.
pub fn read(path: &Path) -> TryConf {
    let content = match fs::read_to_string(path) {
        Err(e) => return TryConf::from_error(e),
        Ok(content) => content,
    };
    match toml::from_str::<TryConf>(&content) {
        Ok(mut conf) => {
            extend_vec_if_indicator_present(&mut conf.conf.doc_valid_idents, DEFAULT_DOC_VALID_IDENTS);
            extend_vec_if_indicator_present(&mut conf.conf.disallowed_names, DEFAULT_DISALLOWED_NAMES);

            conf
        },
        Err(e) => TryConf::from_error(e),
    }
}

fn extend_vec_if_indicator_present(vec: &mut Vec<String>, default: &[&str]) {
    if vec.contains(&"..".to_string()) {
        vec.extend(default.iter().map(ToString::to_string));
    }
}

const SEPARATOR_WIDTH: usize = 4;

// Check whether the error is "unknown field" and, if so, list the available fields sorted and at
// least one per line, more if `CLIPPY_TERMINAL_WIDTH` is set and allows it.
pub fn format_error(error: Box<dyn Error>) -> String {
    let s = error.to_string();

    if_chain! {
        if error.downcast::<toml::de::Error>().is_ok();
        if let Some((prefix, mut fields, suffix)) = parse_unknown_field_message(&s);
        then {
            use fmt::Write;

            fields.sort_unstable();

            let (rows, column_widths) = calculate_dimensions(&fields);

            let mut msg = String::from(prefix);
            for row in 0..rows {
                writeln!(msg).unwrap();
                for (column, column_width) in column_widths.iter().copied().enumerate() {
                    let index = column * rows + row;
                    let field = fields.get(index).copied().unwrap_or_default();
                    write!(
                        msg,
                        "{:SEPARATOR_WIDTH$}{field:column_width$}",
                        " "
                    )
                    .unwrap();
                }
            }
            write!(msg, "\n{suffix}").unwrap();
            msg
        } else {
            s
        }
    }
}

// `parse_unknown_field_message` will become unnecessary if
// https://github.com/alexcrichton/toml-rs/pull/364 is merged.
fn parse_unknown_field_message(s: &str) -> Option<(&str, Vec<&str>, &str)> {
    // An "unknown field" message has the following form:
    //   unknown field `UNKNOWN`, expected one of `FIELD0`, `FIELD1`, ..., `FIELDN` at line X column Y
    //                                           ^^      ^^^^                     ^^
    if_chain! {
        if s.starts_with("unknown field");
        let slices = s.split("`, `").collect::<Vec<_>>();
        let n = slices.len();
        if n >= 2;
        if let Some((prefix, first_field)) = slices[0].rsplit_once(" `");
        if let Some((last_field, suffix)) = slices[n - 1].split_once("` ");
        then {
            let fields = iter::once(first_field)
                .chain(slices[1..n - 1].iter().copied())
                .chain(iter::once(last_field))
                .collect::<Vec<_>>();
            Some((prefix, fields, suffix))
        } else {
            None
        }
    }
}

fn calculate_dimensions(fields: &[&str]) -> (usize, Vec<usize>) {
    let columns = env::var("CLIPPY_TERMINAL_WIDTH")
        .ok()
        .and_then(|s| <usize as FromStr>::from_str(&s).ok())
        .map_or(1, |terminal_width| {
            let max_field_width = fields.iter().map(|field| field.len()).max().unwrap();
            cmp::max(1, terminal_width / (SEPARATOR_WIDTH + max_field_width))
        });

    let rows = (fields.len() + (columns - 1)) / columns;

    let column_widths = (0..columns)
        .map(|column| {
            if column < columns - 1 {
                (0..rows)
                    .map(|row| {
                        let index = column * rows + row;
                        let field = fields.get(index).copied().unwrap_or_default();
                        field.len()
                    })
                    .max()
                    .unwrap()
            } else {
                // Avoid adding extra space to the last column.
                0
            }
        })
        .collect::<Vec<_>>();

    (rows, column_widths)
}