New upstream version 1.25.0+dfsg1

[rustc.git] / src / tools / clippy / clippy_lints / src / const_static_lifetime.rs

use syntax::ast::*;
use rustc::lint::{EarlyContext, EarlyLintPass, LintArray, LintPass};
use utils::{in_macro, snippet, span_lint_and_then};

/// **What it does:** Checks for constants with an explicit `'static` lifetime.
///
/// **Why is this bad?** Adding `'static` to every reference can create very
/// complicated types.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// const FOO: &'static [(&'static str, &'static str, fn(&Bar) -> bool)] =
/// &[...]
/// ```
/// This code can be rewritten as
/// ```rust
///  const FOO: &[(&str, &str, fn(&Bar) -> bool)] = &[...]
/// ```
declare_lint! {
    pub CONST_STATIC_LIFETIME,
    Warn,
    "Using explicit `'static` lifetime for constants when elision rules would allow omitting them."
}

pub struct StaticConst;

impl LintPass for StaticConst {
    fn get_lints(&self) -> LintArray {
        lint_array!(CONST_STATIC_LIFETIME)
    }
}

impl StaticConst {
    // Recursively visit types
    fn visit_type(&mut self, ty: &Ty, cx: &EarlyContext) {
        match ty.node {
            // Be careful of nested structures (arrays and tuples)
            TyKind::Array(ref ty, _) => {
                self.visit_type(&*ty, cx);
            },
            TyKind::Tup(ref tup) => for tup_ty in tup {
                self.visit_type(&*tup_ty, cx);
            },
            // This is what we are looking for !
            TyKind::Rptr(ref optional_lifetime, ref borrow_type) => {
                // Match the 'static lifetime
                if let Some(lifetime) = *optional_lifetime {
                    match borrow_type.ty.node {
                        TyKind::Path(..) | TyKind::Slice(..) | TyKind::Array(..) |
                        TyKind::Tup(..) => {
                            if lifetime.ident.name == "'static" {
                                let snip = snippet(cx, borrow_type.ty.span, "<type>");
                                let sugg = format!("&{}", snip);
                                span_lint_and_then(
                                    cx,
                                    CONST_STATIC_LIFETIME,
                                    lifetime.span,
                                    "Constants have by default a `'static` lifetime",
                                    |db| {
                                        db.span_suggestion(ty.span, "consider removing `'static`", sugg);
                                    },
                                );
                            }
                        }
                        _ => {}
                    }
                }
                self.visit_type(&*borrow_type.ty, cx);
            },
            TyKind::Slice(ref ty) => {
                self.visit_type(ty, cx);
            },
            _ => {},
        }
    }
}

impl EarlyLintPass for StaticConst {
    fn check_item(&mut self, cx: &EarlyContext, item: &Item) {
        if !in_macro(item.span) {
            // Match only constants...
            if let ItemKind::Const(ref var_type, _) = item.node {
                self.visit_type(var_type, cx);
            }
        }
    }

    fn check_trait_item(&mut self, cx: &EarlyContext, item: &TraitItem) {
        if !in_macro(item.span) {
            // Match only constants...
            if let TraitItemKind::Const(ref var_type, _) = item.node {
                self.visit_type(var_type, cx);
            }
        }
    }

    fn check_impl_item(&mut self, cx: &EarlyContext, item: &ImplItem) {
        if !in_macro(item.span) {
            // Match only constants...
            if let ImplItemKind::Const(ref var_type, _) = item.node {
                self.visit_type(var_type, cx);
            }
        }
    }
}