rust/clippy_lints/src/replace_consts.rs

use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
use rustc::{declare_lint, lint_array};
use if_chain::if_chain;
use rustc::hir;
use rustc::hir::def::Def;
use crate::utils::{match_def_path, span_lint_and_sugg};

/// **What it does:** Checks for usage of `ATOMIC_X_INIT`, `ONCE_INIT`, and
/// `uX/iX::MIN/MAX`.
///
/// **Why is this bad?** `const fn`s exist
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// static FOO: AtomicIsize = ATOMIC_ISIZE_INIT;
/// ```
///
/// Could be written:
///
/// ```rust
/// static FOO: AtomicIsize = AtomicIsize::new(0);
/// ```
declare_clippy_lint! {
    pub REPLACE_CONSTS,
    pedantic,
    "Lint usages of standard library `const`s that could be replaced by `const fn`s"
}

pub struct ReplaceConsts;

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

impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ReplaceConsts {
    fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr) {
        if_chain! {
            if let hir::ExprKind::Path(ref qp) = expr.node;
            if let Def::Const(def_id) = cx.tables.qpath_def(qp, expr.hir_id);
            then {
                for &(const_path, repl_snip) in REPLACEMENTS {
                    if match_def_path(cx.tcx, def_id, const_path) {
                        span_lint_and_sugg(
                            cx,
                            REPLACE_CONSTS,
                            expr.span,
                            &format!("using `{}`", const_path.last().expect("empty path")),
                            "try this",
                            repl_snip.to_string(),
                        );
                        return;
                    }
                }
            }
        }
    }
}

const REPLACEMENTS: &[(&[&str], &str)] = &[
    // Once
    (&["core", "sync",  "ONCE_INIT"], "Once::new()"),
    // Atomic
    (&["core", "sync", "atomic", "ATOMIC_BOOL_INIT"],  "AtomicBool::new(false)"),
    (&["core", "sync", "atomic", "ATOMIC_ISIZE_INIT"], "AtomicIsize::new(0)"),
    (&["core", "sync", "atomic", "ATOMIC_I8_INIT"],    "AtomicI8::new(0)"),
    (&["core", "sync", "atomic", "ATOMIC_I16_INIT"],   "AtomicI16::new(0)"),
    (&["core", "sync", "atomic", "ATOMIC_I32_INIT"],   "AtomicI32::new(0)"),
    (&["core", "sync", "atomic", "ATOMIC_I64_INIT"],   "AtomicI64::new(0)"),
    (&["core", "sync", "atomic", "ATOMIC_USIZE_INIT"], "AtomicUsize::new(0)"),
    (&["core", "sync", "atomic", "ATOMIC_U8_INIT"],    "AtomicU8::new(0)"),
    (&["core", "sync", "atomic", "ATOMIC_U16_INIT"],   "AtomicU16::new(0)"),
    (&["core", "sync", "atomic", "ATOMIC_U32_INIT"],   "AtomicU32::new(0)"),
    (&["core", "sync", "atomic", "ATOMIC_U64_INIT"],   "AtomicU64::new(0)"),
    // Min
    (&["core", "isize", "MIN"], "isize::min_value()"),
    (&["core", "i8",    "MIN"], "i8::min_value()"),
    (&["core", "i16",   "MIN"], "i16::min_value()"),
    (&["core", "i32",   "MIN"], "i32::min_value()"),
    (&["core", "i64",   "MIN"], "i64::min_value()"),
    (&["core", "i128",  "MIN"], "i128::min_value()"),
    (&["core", "usize", "MIN"], "usize::min_value()"),
    (&["core", "u8",    "MIN"], "u8::min_value()"),
    (&["core", "u16",   "MIN"], "u16::min_value()"),
    (&["core", "u32",   "MIN"], "u32::min_value()"),
    (&["core", "u64",   "MIN"], "u64::min_value()"),
    (&["core", "u128",  "MIN"], "u128::min_value()"),
    // Max
    (&["core", "isize", "MAX"], "isize::max_value()"),
    (&["core", "i8",    "MAX"], "i8::max_value()"),
    (&["core", "i16",   "MAX"], "i16::max_value()"),
    (&["core", "i32",   "MAX"], "i32::max_value()"),
    (&["core", "i64",   "MAX"], "i64::max_value()"),
    (&["core", "i128",  "MAX"], "i128::max_value()"),
    (&["core", "usize", "MAX"], "usize::max_value()"),
    (&["core", "u8",    "MAX"], "u8::max_value()"),
    (&["core", "u16",   "MAX"], "u16::max_value()"),
    (&["core", "u32",   "MAX"], "u32::max_value()"),
    (&["core", "u64",   "MAX"], "u64::max_value()"),
    (&["core", "u128",  "MAX"], "u128::max_value()"),
];