enum_variants.rs

//! lint on enum variants that are prefixed or suffixed by the same characters

use clippy_utils::diagnostics::{span_lint, span_lint_and_help, span_lint_hir};
use clippy_utils::source::is_present_in_source;
use clippy_utils::str_utils::{camel_case_split, count_match_end, count_match_start};
use rustc_hir::{EnumDef, Item, ItemKind, OwnerId, Variant};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_tool_lint, impl_lint_pass};
use rustc_span::source_map::Span;
use rustc_span::symbol::Symbol;

declare_clippy_lint! {
    /// ### What it does
    /// Detects enumeration variants that are prefixed or suffixed
    /// by the same characters.
    ///
    /// ### Why is this bad?
    /// Enumeration variant names should specify their variant,
    /// not repeat the enumeration name.
    ///
    /// ### Limitations
    /// Characters with no casing will be considered when comparing prefixes/suffixes
    /// This applies to numbers and non-ascii characters without casing
    /// e.g. `Foo1` and `Foo2` is considered to have different prefixes
    /// (the prefixes are `Foo1` and `Foo2` respectively), as also `Bar螃`, `Bar蟹`
    ///
    /// ### Example
    /// ```rust
    /// enum Cake {
    ///     BlackForestCake,
    ///     HummingbirdCake,
    ///     BattenbergCake,
    /// }
    /// ```
    /// Use instead:
    /// ```rust
    /// enum Cake {
    ///     BlackForest,
    ///     Hummingbird,
    ///     Battenberg,
    /// }
    /// ```
    #[clippy::version = "pre 1.29.0"]
    pub ENUM_VARIANT_NAMES,
    style,
    "enums where all variants share a prefix/postfix"
}

declare_clippy_lint! {
    /// ### What it does
    /// Detects type names that are prefixed or suffixed by the
    /// containing module's name.
    ///
    /// ### Why is this bad?
    /// It requires the user to type the module name twice.
    ///
    /// ### Example
    /// ```rust
    /// mod cake {
    ///     struct BlackForestCake;
    /// }
    /// ```
    ///
    /// Use instead:
    /// ```rust
    /// mod cake {
    ///     struct BlackForest;
    /// }
    /// ```
    #[clippy::version = "1.33.0"]
    pub MODULE_NAME_REPETITIONS,
    pedantic,
    "type names prefixed/postfixed with their containing module's name"
}

declare_clippy_lint! {
    /// ### What it does
    /// Checks for modules that have the same name as their
    /// parent module
    ///
    /// ### Why is this bad?
    /// A typical beginner mistake is to have `mod foo;` and
    /// again `mod foo { ..
    /// }` in `foo.rs`.
    /// The expectation is that items inside the inner `mod foo { .. }` are then
    /// available
    /// through `foo::x`, but they are only available through
    /// `foo::foo::x`.
    /// If this is done on purpose, it would be better to choose a more
    /// representative module name.
    ///
    /// ### Example
    /// ```ignore
    /// // lib.rs
    /// mod foo;
    /// // foo.rs
    /// mod foo {
    ///     ...
    /// }
    /// ```
    #[clippy::version = "pre 1.29.0"]
    pub MODULE_INCEPTION,
    style,
    "modules that have the same name as their parent module"
}

pub struct EnumVariantNames {
    modules: Vec<(Symbol, String, OwnerId)>,
    threshold: u64,
    avoid_breaking_exported_api: bool,
    allow_private_module_inception: bool,
}

impl EnumVariantNames {
    #[must_use]
    pub fn new(threshold: u64, avoid_breaking_exported_api: bool, allow_private_module_inception: bool) -> Self {
        Self {
            modules: Vec::new(),
            threshold,
            avoid_breaking_exported_api,
            allow_private_module_inception,
        }
    }
}

impl_lint_pass!(EnumVariantNames => [
    ENUM_VARIANT_NAMES,
    MODULE_NAME_REPETITIONS,
    MODULE_INCEPTION
]);

fn check_enum_start(cx: &LateContext<'_>, item_name: &str, variant: &Variant<'_>) {
    let name = variant.ident.name.as_str();
    let item_name_chars = item_name.chars().count();

    if count_match_start(item_name, name).char_count == item_name_chars
        && name.chars().nth(item_name_chars).map_or(false, |c| !c.is_lowercase())
        && name.chars().nth(item_name_chars + 1).map_or(false, |c| !c.is_numeric())
    {
        span_lint_hir(
            cx,
            ENUM_VARIANT_NAMES,
            variant.hir_id,
            variant.span,
            "variant name starts with the enum's name",
        );
    }
}

fn check_enum_end(cx: &LateContext<'_>, item_name: &str, variant: &Variant<'_>) {
    let name = variant.ident.name.as_str();
    let item_name_chars = item_name.chars().count();

    if count_match_end(item_name, name).char_count == item_name_chars {
        span_lint_hir(
            cx,
            ENUM_VARIANT_NAMES,
            variant.hir_id,
            variant.span,
            "variant name ends with the enum's name",
        );
    }
}

fn check_variant(cx: &LateContext<'_>, threshold: u64, def: &EnumDef<'_>, item_name: &str, span: Span) {
    if (def.variants.len() as u64) < threshold {
        return;
    }

    let first = &def.variants[0].ident.name.as_str();
    let mut pre = camel_case_split(first);
    let mut post = pre.clone();
    post.reverse();
    for var in def.variants {
        check_enum_start(cx, item_name, var);
        check_enum_end(cx, item_name, var);
        let name = var.ident.name.as_str();

        let variant_split = camel_case_split(name);
        if variant_split.len() == 1 {
            return;
        }

        pre = pre
            .iter()
            .zip(variant_split.iter())
            .take_while(|(a, b)| a == b)
            .map(|e| *e.0)
            .collect();
        post = post
            .iter()
            .zip(variant_split.iter().rev())
            .take_while(|(a, b)| a == b)
            .map(|e| *e.0)
            .collect();
    }
    let (what, value) = match (have_no_extra_prefix(&pre), post.is_empty()) {
        (true, true) => return,
        (false, _) => ("pre", pre.join("")),
        (true, false) => {
            post.reverse();
            ("post", post.join(""))
        },
    };
    span_lint_and_help(
        cx,
        ENUM_VARIANT_NAMES,
        span,
        &format!("all variants have the same {what}fix: `{value}`"),
        None,
        &format!(
            "remove the {what}fixes and use full paths to \
             the variants instead of glob imports"
        ),
    );
}

#[must_use]
fn have_no_extra_prefix(prefixes: &[&str]) -> bool {
    prefixes.iter().all(|p| p == &"" || p == &"_")
}

#[must_use]
fn to_camel_case(item_name: &str) -> String {
    let mut s = String::new();
    let mut up = true;
    for c in item_name.chars() {
        if c.is_uppercase() {
            // we only turn snake case text into CamelCase
            return item_name.to_string();
        }
        if c == '_' {
            up = true;
            continue;
        }
        if up {
            up = false;
            s.extend(c.to_uppercase());
        } else {
            s.push(c);
        }
    }
    s
}

impl LateLintPass<'_> for EnumVariantNames {
    fn check_item_post(&mut self, _cx: &LateContext<'_>, _item: &Item<'_>) {
        let last = self.modules.pop();
        assert!(last.is_some());
    }

    #[expect(clippy::similar_names)]
    fn check_item(&mut self, cx: &LateContext<'_>, item: &Item<'_>) {
        let item_name = item.ident.name.as_str();
        let item_camel = to_camel_case(item_name);
        if !item.span.from_expansion() && is_present_in_source(cx, item.span) {
            if let [.., (mod_name, mod_camel, owner_id)] = &*self.modules {
                // constants don't have surrounding modules
                if !mod_camel.is_empty() {
                    if mod_name == &item.ident.name
                        && let ItemKind::Mod(..) = item.kind
                        && (!self.allow_private_module_inception || cx.tcx.visibility(owner_id.def_id).is_public())
                    {
                        span_lint(
                            cx,
                            MODULE_INCEPTION,
                            item.span,
                            "module has the same name as its containing module",
                        );
                    }
                    // The `module_name_repetitions` lint should only trigger if the item has the module in its
                    // name. Having the same name is accepted.
                    if cx.tcx.visibility(item.owner_id).is_public() && item_camel.len() > mod_camel.len() {
                        let matching = count_match_start(mod_camel, &item_camel);
                        let rmatching = count_match_end(mod_camel, &item_camel);
                        let nchars = mod_camel.chars().count();

                        let is_word_beginning = |c: char| c == '_' || c.is_uppercase() || c.is_numeric();

                        if matching.char_count == nchars {
                            match item_camel.chars().nth(nchars) {
                                Some(c) if is_word_beginning(c) => span_lint(
                                    cx,
                                    MODULE_NAME_REPETITIONS,
                                    item.ident.span,
                                    "item name starts with its containing module's name",
                                ),
                                _ => (),
                            }
                        }
                        if rmatching.char_count == nchars {
                            span_lint(
                                cx,
                                MODULE_NAME_REPETITIONS,
                                item.ident.span,
                                "item name ends with its containing module's name",
                            );
                        }
                    }
                }
            }
        }
        if let ItemKind::Enum(ref def, _) = item.kind {
            if !(self.avoid_breaking_exported_api && cx.effective_visibilities.is_exported(item.owner_id.def_id)) {
                check_variant(cx, self.threshold, def, item_name, item.span);
            }
        }
        self.modules.push((item.ident.name, item_camel, item.owner_id));
    }
}