Add lint to replace consts with const fns

clippy_lints/src/lib.rs

@@ -150,6 +150,7 @@ pub mod ptr;
 pub mod ranges;
 pub mod reference;
 pub mod regex;
+pub mod replace_consts;
 pub mod returns;
 pub mod serde_api;
 pub mod shadow;
@@ -361,6 +362,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry) {
     reg.register_late_lint_pass(box types::ImplicitHasher);
     reg.register_early_lint_pass(box const_static_lifetime::StaticConst);
     reg.register_late_lint_pass(box fallible_impl_from::FallibleImplFrom);
+    reg.register_late_lint_pass(box replace_consts::ReplaceConsts);
 
     reg.register_lint_group("clippy_restrictions", vec![
         arithmetic::FLOAT_ARITHMETIC,
@@ -399,6 +401,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry) {
         print::PRINT_STDOUT,
         print::USE_DEBUG,
         ranges::RANGE_PLUS_ONE,
+        replace_consts::REPLACE_CONSTS,
         shadow::SHADOW_REUSE,
         shadow::SHADOW_SAME,
         shadow::SHADOW_UNRELATED,

clippy_lints/src/replace_consts.rs

@@ -0,0 +1,102 @@
+use rustc::lint::*;
+use rustc::hir;
+use rustc::hir::def::Def;
+use 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_lint! {
+    pub REPLACE_CONSTS,
+    Allow,
+    "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::ExprPath(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()"),
+];