Auto merge of #5429 - faern:use-assoc-int-float-consts, r=flip1995

Use assoc int and float consts instead of module level ones

changelog: Recommend primitive type associated constants instead of module level constants

In Rust 1.43 integer and float primitive types will have a number of new associated constants. For example `MAX`, `MIN` and a number of constants related to the machine representation of floats. rust-lang/rust#68952

These new constants are preferred over the module level constants in `{core,std}::{f*, u*, i*}`. I have in the last few days made sure that the documentation in the main rust repository uses the new constants in every place I could find (rust-lang/rust#69860, rust-lang/rust#70782). So the next step is naturally to make the linter recommend the new constants as well.

This PR only changes two lints. There are more. But I did not want the PR to be too big. And since I have not contributed to clippy before it felt saner to start with a small PR so I see if there are any quirks. More will come later.

Author: bors

clippy_lints/src/checked_conversions.rs

@@ -21,7 +21,7 @@ declare_clippy_lint! {
     /// ```rust
     /// # let foo: u32 = 5;
     /// # let _ =
-    /// foo <= i32::max_value() as u32
+    /// foo <= i32::MAX as u32
     /// # ;
     /// ```
     ///
@@ -179,7 +179,7 @@ impl ConversionType {
     }
 }
 
-/// Check for `expr <= (to_type::max_value() as from_type)`
+/// Check for `expr <= (to_type::MAX as from_type)`
 fn check_upper_bound<'tcx>(expr: &'tcx Expr<'tcx>) -> Option<Conversion<'tcx>> {
     if_chain! {
          if let ExprKind::Binary(ref op, ref left, ref right) = &expr.kind;
@@ -194,7 +194,7 @@ fn check_upper_bound<'tcx>(expr: &'tcx Expr<'tcx>) -> Option<Conversion<'tcx>> {
     }
 }
 
-/// Check for `expr >= 0|(to_type::min_value() as from_type)`
+/// Check for `expr >= 0|(to_type::MIN as from_type)`
 fn check_lower_bound<'tcx>(expr: &'tcx Expr<'tcx>) -> Option<Conversion<'tcx>> {
     fn check_function<'a>(candidate: &'a Expr<'a>, check: &'a Expr<'a>) -> Option<Conversion<'a>> {
         (check_lower_bound_zero(candidate, check)).or_else(|| (check_lower_bound_min(candidate, check)))
@@ -222,7 +222,7 @@ fn check_lower_bound_zero<'a>(candidate: &'a Expr<'_>, check: &'a Expr<'_>) -> O
     }
 }
 
-/// Check for `expr >= (to_type::min_value() as from_type)`
+/// Check for `expr >= (to_type::MIN as from_type)`
 fn check_lower_bound_min<'a>(candidate: &'a Expr<'_>, check: &'a Expr<'_>) -> Option<Conversion<'a>> {
     if let Some((from, to)) = get_types_from_cast(check, MIN_VALUE, SINTS) {
         Conversion::try_new(candidate, from, to)

clippy_lints/src/float_literal.rs

@@ -6,7 +6,7 @@ use rustc_hir as hir;
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::ty;
 use rustc_session::{declare_lint_pass, declare_tool_lint};
-use std::{f32, f64, fmt};
+use std::fmt;
 
 declare_clippy_lint! {
     /// **What it does:** Checks for float literals with a precision greater

clippy_lints/src/methods/mod.rs

@@ -1138,8 +1138,8 @@ declare_clippy_lint! {
     /// ```rust
     /// # let y: u32 = 0;
     /// # let x: u32 = 100;
-    /// let add = x.checked_add(y).unwrap_or(u32::max_value());
-    /// let sub = x.checked_sub(y).unwrap_or(u32::min_value());
+    /// let add = x.checked_add(y).unwrap_or(u32::MAX);
+    /// let sub = x.checked_sub(y).unwrap_or(u32::MIN);
     /// ```
     ///
     /// can be written using dedicated methods for saturating addition/subtraction as:

clippy_lints/src/misc.rs

@@ -57,10 +57,9 @@ declare_clippy_lint! {
     ///
     /// **Example:**
     /// ```rust
-    /// # use core::f32::NAN;
     /// # let x = 1.0;
     ///
-    /// if x == NAN { }
+    /// if x == f32::NAN { }
     /// ```
     pub CMP_NAN,
     correctness,
@@ -389,7 +388,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MiscLints {
                             ),
                             Applicability::HasPlaceholders, // snippet
                         );
-                        db.span_note(expr.span, "`std::f32::EPSILON` and `std::f64::EPSILON` are available.");
+                        db.span_note(expr.span, "`f32::EPSILON` and `f64::EPSILON` are available.");
                     });
                 } else if op == BinOpKind::Rem && is_integer_const(cx, right, 1) {
                     span_lint(cx, MODULO_ONE, expr.span, "any number modulo 1 will be 0");
@@ -457,7 +456,7 @@ fn check_nan(cx: &LateContext<'_, '_>, expr: &Expr<'_>, cmp_expr: &Expr<'_>) {
                     cx,
                     CMP_NAN,
                     cmp_expr.span,
-                    "doomed comparison with `NAN`, use `std::{f32,f64}::is_nan()` instead",
+                    "doomed comparison with `NAN`, use `{f32,f64}::is_nan()` instead",
                 );
             }
         }

clippy_lints/src/neg_cmp_op_on_partial_ord.rs

@@ -25,13 +25,13 @@ declare_clippy_lint! {
     ///
     /// // Bad
     /// let a = 1.0;
-    /// let b = std::f64::NAN;
+    /// let b = f64::NAN;
     ///
     /// let _not_less_or_equal = !(a <= b);
     ///
     /// // Good
     /// let a = 1.0;
-    /// let b = std::f64::NAN;
+    /// let b = f64::NAN;
     ///
     /// let _not_less_or_equal = match a.partial_cmp(&b) {
     ///     None | Some(Ordering::Greater) => true,

clippy_lints/src/types.rs

@@ -837,7 +837,7 @@ declare_clippy_lint! {
     ///
     /// **Example:**
     /// ```rust
-    /// let x = std::u64::MAX;
+    /// let x = u64::MAX;
     /// x as f64;
     /// ```
     pub CAST_PRECISION_LOSS,
@@ -904,7 +904,7 @@ declare_clippy_lint! {
     ///
     /// **Example:**
     /// ```rust
-    /// std::u32::MAX as i32; // will yield a value of `-1`
+    /// u32::MAX as i32; // will yield a value of `-1`
     /// ```
     pub CAST_POSSIBLE_WRAP,
     pedantic,
@@ -1752,7 +1752,7 @@ declare_clippy_lint! {
     /// ```rust
     /// let vec: Vec<isize> = Vec::new();
     /// if vec.len() <= 0 {}
-    /// if 100 > std::i32::MAX {}
+    /// if 100 > i32::MAX {}
     /// ```
     pub ABSURD_EXTREME_COMPARISONS,
     correctness,
@@ -1973,8 +1973,6 @@ impl Ord for FullInt {
 }
 
 fn numeric_cast_precast_bounds<'a>(cx: &LateContext<'_, '_>, expr: &'a Expr<'_>) -> Option<(FullInt, FullInt)> {
-    use std::{i128, i16, i32, i64, i8, isize, u128, u16, u32, u64, u8, usize};
-
     if let ExprKind::Cast(ref cast_exp, _) = expr.kind {
         let pre_cast_ty = cx.tables.expr_ty(cast_exp);
         let cast_ty = cx.tables.expr_ty(expr);

clippy_lints/src/utils/diagnostics.rs

@@ -60,7 +60,7 @@ pub fn span_lint<T: LintContext>(cx: &T, lint: &'static Lint, sp: impl Into<Mult
 /// 6  |     let other_f64_nan = 0.0f64 / 0.0;
 ///    |                         ^^^^^^^^^^^^
 ///    |
-///    = help: Consider using `std::f64::NAN` if you would like a constant representing NaN
+///    = help: Consider using `f64::NAN` if you would like a constant representing NaN
 /// ```
 pub fn span_lint_and_help<'a, T: LintContext>(cx: &'a T, lint: &'static Lint, span: Span, msg: &str, help: &str) {
     cx.struct_span_lint(lint, span, |ldb| {

clippy_lints/src/zero_div_zero.rs

@@ -8,8 +8,7 @@ use rustc_session::{declare_lint_pass, declare_tool_lint};
 declare_clippy_lint! {
     /// **What it does:** Checks for `0.0 / 0.0`.
     ///
-    /// **Why is this bad?** It's less readable than `std::f32::NAN` or
-    /// `std::f64::NAN`.
+    /// **Why is this bad?** It's less readable than `f32::NAN` or `f64::NAN`.
     ///
     /// **Known problems:** None.
     ///
@@ -19,7 +18,7 @@ declare_clippy_lint! {
     /// ```
     pub ZERO_DIVIDED_BY_ZERO,
     complexity,
-    "usage of `0.0 / 0.0` to obtain NaN instead of `std::f32::NAN` or `std::f64::NAN`"
+    "usage of `0.0 / 0.0` to obtain NaN instead of `f32::NAN` or `f64::NAN`"
 }
 
 declare_lint_pass!(ZeroDiv => [ZERO_DIVIDED_BY_ZERO]);
@@ -38,7 +37,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ZeroDiv {
             if Constant::F32(0.0) == lhs_value || Constant::F64(0.0) == lhs_value;
             if Constant::F32(0.0) == rhs_value || Constant::F64(0.0) == rhs_value;
             then {
-                // since we're about to suggest a use of std::f32::NaN or std::f64::NaN,
+                // since we're about to suggest a use of f32::NAN or f64::NAN,
                 // match the precision of the literals that are given.
                 let float_type = match (lhs_value, rhs_value) {
                     (Constant::F64(_), _)
@@ -51,7 +50,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ZeroDiv {
                     expr.span,
                     "constant division of `0.0` with `0.0` will always result in NaN",
                     &format!(
-                        "Consider using `std::{}::NAN` if you would like a constant representing NaN",
+                        "Consider using `{}::NAN` if you would like a constant representing NaN",
                         float_type,
                     ),
                 );

src/lintlist/mod.rs

@@ -2526,7 +2526,7 @@ pub static ref ALL_LINTS: Vec<Lint> = vec![
     Lint {
         name: "zero_divided_by_zero",
         group: "complexity",
-        desc: "usage of `0.0 / 0.0` to obtain NaN instead of `std::f32::NAN` or `std::f64::NAN`",
+        desc: "usage of `0.0 / 0.0` to obtain NaN instead of `f32::NAN` or `f64::NAN`",
         deprecation: None,
         module: "zero_div_zero",
     },

tests/ui/absurd-extreme-comparisons.rs

@@ -16,17 +16,17 @@ fn main() {
     u < Z;
     Z >= u;
     Z > u;
-    u > std::u32::MAX;
-    u >= std::u32::MAX;
-    std::u32::MAX < u;
-    std::u32::MAX <= u;
+    u > u32::MAX;
+    u >= u32::MAX;
+    u32::MAX < u;
+    u32::MAX <= u;
     1-1 > u;
     u >= !0;
     u <= 12 - 2*6;
     let i: i8 = 0;
     i < -127 - 1;
-    std::i8::MAX >= i;
-    3-7 < std::i32::MIN;
+    i8::MAX >= i;
+    3-7 < i32::MIN;
     let b = false;
     b >= true;
     false > b;
@@ -52,10 +52,10 @@ impl PartialOrd<u32> for U {
 }
 
 pub fn foo(val: U) -> bool {
-    val > std::u32::MAX
+    val > u32::MAX
 }
 
 pub fn bar(len: u64) -> bool {
     // This is OK as we are casting from target sized to fixed size
-    len >= std::usize::MAX as u64
+    len >= usize::MAX as u64
 }