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Supress excessive_precision when constants are overly precise
Added const associated items matching and static Added configurable threshold Addressed comments Renamed lint config field
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‎CHANGELOG.md‎

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@@ -6712,6 +6712,7 @@ Released 2018-09-13
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[`check-inconsistent-struct-field-initializers`]: https://doc.rust-lang.org/clippy/lint_configuration.html#check-inconsistent-struct-field-initializers
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[`check-private-items`]: https://doc.rust-lang.org/clippy/lint_configuration.html#check-private-items
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[`cognitive-complexity-threshold`]: https://doc.rust-lang.org/clippy/lint_configuration.html#cognitive-complexity-threshold
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[`const-literal-digits-threshold`]: https://doc.rust-lang.org/clippy/lint_configuration.html#const-literal-digits-threshold
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[`disallowed-macros`]: https://doc.rust-lang.org/clippy/lint_configuration.html#disallowed-macros
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[`disallowed-methods`]: https://doc.rust-lang.org/clippy/lint_configuration.html#disallowed-methods
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[`disallowed-names`]: https://doc.rust-lang.org/clippy/lint_configuration.html#disallowed-names

‎book/src/lint_configuration.md‎

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@@ -485,6 +485,16 @@ The maximum cognitive complexity a function can have
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* [`cognitive_complexity`](https://rust-lang.github.io/rust-clippy/master/index.html#cognitive_complexity)
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## `const-literal-digits-threshold`
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The minimum digits a const float literal must have to supress the `excessive_precicion` lint
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**Default Value:** `30`
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---
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**Affected lints:**
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* [`excessive_precision`](https://rust-lang.github.io/rust-clippy/master/index.html#excessive_precision)
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## `disallowed-macros`
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The list of disallowed macros, written as fully qualified paths.
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‎clippy_config/src/conf.rs‎

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@@ -570,6 +570,9 @@ define_Conf! {
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/// The maximum cognitive complexity a function can have
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#[lints(cognitive_complexity)]
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cognitive_complexity_threshold: u64 = 25,
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/// The minimum digits a const float literal must have to supress the `excessive_precicion` lint
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#[lints(excessive_precision)]
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const_literal_digits_threshold: usize = 30,
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/// DEPRECATED LINT: CYCLOMATIC_COMPLEXITY.
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///
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/// Use the Cognitive Complexity lint instead.

‎clippy_lints/src/float_literal.rs‎

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@@ -1,18 +1,21 @@
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use clippy_config::Conf;
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use clippy_utils::diagnostics::span_lint_and_then;
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use clippy_utils::numeric_literal;
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use clippy_utils::{ExprUseNode, expr_use_ctxt, numeric_literal};
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use rustc_ast::ast::{LitFloatType, LitKind};
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use rustc_errors::Applicability;
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use rustc_hir as hir;
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::ty::{self, FloatTy};
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use rustc_session::declare_lint_pass;
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use rustc_session::impl_lint_pass;
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use std::fmt;
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for float literals with a precision greater
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/// than that supported by the underlying type.
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///
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/// The lint is suppressed for literals with over `const_literal_digits_threshold` digits.
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///
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/// ### Why is this bad?
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/// Rust will truncate the literal silently.
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///
@@ -58,7 +61,21 @@ declare_clippy_lint! {
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"lossy whole number float literals"
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}
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declare_lint_pass!(FloatLiteral => [EXCESSIVE_PRECISION, LOSSY_FLOAT_LITERAL]);
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pub struct FloatLiteral {
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const_literal_digits_threshold: usize,
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}
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impl_lint_pass!(FloatLiteral => [
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EXCESSIVE_PRECISION, LOSSY_FLOAT_LITERAL
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]);
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impl FloatLiteral {
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pub fn new(conf: &'static Conf) -> Self {
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Self {
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const_literal_digits_threshold: conf.const_literal_digits_threshold,
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}
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}
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}
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impl<'tcx> LateLintPass<'tcx> for FloatLiteral {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
@@ -126,13 +143,25 @@ impl<'tcx> LateLintPass<'tcx> for FloatLiteral {
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},
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);
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}
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} else if digits > max as usize && count_digits(&float_str) < count_digits(sym_str) {
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} else if digits > max as usize && count_digits(&float_str) < digits {
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if digits >= self.const_literal_digits_threshold
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&& matches!(expr_use_ctxt(cx, expr).use_node(cx), ExprUseNode::ConstStatic(_))
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{
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// If a big enough number of digits is specified and it's a constant
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// we assume the user is definining a constant, and excessive precision is ok
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return;
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}
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span_lint_and_then(
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cx,
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EXCESSIVE_PRECISION,
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expr.span,
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"float has excessive precision",
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|diag| {
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if digits >= self.const_literal_digits_threshold
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&& let Some(let_stmt) = maybe_let_stmt(cx, expr)
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{
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diag.span_note(let_stmt.span, "consider making it a `const` item");
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}
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diag.span_suggestion_verbose(
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expr.span,
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"consider changing the type or truncating it to",
@@ -196,3 +225,11 @@ impl FloatFormat {
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}
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}
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}
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fn maybe_let_stmt<'a>(cx: &LateContext<'a>, expr: &hir::Expr<'_>) -> Option<&'a hir::LetStmt<'a>> {
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let parent = cx.tcx.parent_hir_node(expr.hir_id);
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match parent {
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hir::Node::LetStmt(let_stmt) => Some(let_stmt),
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_ => None,
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}
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}

‎clippy_lints/src/lib.rs‎

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@@ -475,7 +475,7 @@ pub fn register_lint_passes(store: &mut rustc_lint::LintStore, conf: &'static Co
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store.register_late_pass(move |_| Box::new(types::Types::new(conf)));
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store.register_late_pass(move |_| Box::new(booleans::NonminimalBool::new(conf)));
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store.register_late_pass(|_| Box::new(enum_clike::UnportableVariant));
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store.register_late_pass(|_| Box::new(float_literal::FloatLiteral));
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store.register_late_pass(move |_| Box::new(float_literal::FloatLiteral::new(conf)));
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store.register_late_pass(|_| Box::new(ptr::Ptr));
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store.register_late_pass(|_| Box::new(needless_bool::NeedlessBool));
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store.register_late_pass(|_| Box::new(bool_comparison::BoolComparison));

‎tests/ui-toml/excessive_precision/clippy.toml‎

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const-literal-digits-threshold = 20

‎tests/ui-toml/excessive_precision/excessive_precision.fixed‎

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#![warn(clippy::excessive_precision)]
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#![allow(
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dead_code,
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overflowing_literals,
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unused_variables,
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clippy::print_literal,
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clippy::useless_vec
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)]
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fn main() {
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// Overly specified constants
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let _: f32 = 1.012_345_7;
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//~^ excessive_precision
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let _: f64 = 1.012_345_678_901_234_6;
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//~^ excessive_precision
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const _: f32 = 1.012345678901234567890;
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const _: f64 = 1.012345678901234567890;
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static STATIC1: f32 = 1.012345678901234567890;
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static STATIC2: f64 = 1.012345678901234567890;
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static mut STATIC_MUT1: f32 = 1.012345678901234567890;
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static mut STATIC_MUT2: f64 = 1.012345678901234567890;
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}
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trait ExcessivelyPreciseTrait {
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// Overly specified constants
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const GOOD1: f32 = 1.012345678901234567890;
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const GOOD2: f64 = 1.012345678901234567890;
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}
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struct ExcessivelyPreciseStruct;
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impl ExcessivelyPreciseStruct {
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// Overly specified constants
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const GOOD1: f32 = 1.012345678901234567890;
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const GOOD2: f64 = 1.012345678901234567890;
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}

‎tests/ui-toml/excessive_precision/excessive_precision.rs‎

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#![warn(clippy::excessive_precision)]
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#![allow(
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dead_code,
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overflowing_literals,
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unused_variables,
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clippy::print_literal,
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clippy::useless_vec
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)]
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fn main() {
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// Overly specified constants
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let _: f32 = 1.012345678901234567890;
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//~^ excessive_precision
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let _: f64 = 1.012345678901234567890;
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//~^ excessive_precision
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const _: f32 = 1.012345678901234567890;
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const _: f64 = 1.012345678901234567890;
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static STATIC1: f32 = 1.012345678901234567890;
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static STATIC2: f64 = 1.012345678901234567890;
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static mut STATIC_MUT1: f32 = 1.012345678901234567890;
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static mut STATIC_MUT2: f64 = 1.012345678901234567890;
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}
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trait ExcessivelyPreciseTrait {
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// Overly specified constants
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const GOOD1: f32 = 1.012345678901234567890;
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const GOOD2: f64 = 1.012345678901234567890;
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}
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struct ExcessivelyPreciseStruct;
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impl ExcessivelyPreciseStruct {
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// Overly specified constants
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const GOOD1: f32 = 1.012345678901234567890;
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const GOOD2: f64 = 1.012345678901234567890;
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}

‎tests/ui-toml/excessive_precision/excessive_precision.stderr‎

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error: float has excessive precision
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--> tests/ui-toml/excessive_precision/excessive_precision.rs:12:18
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|
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LL | let _: f32 = 1.012345678901234567890;
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| ^^^^^^^^^^^^^^^^^^^^^^^
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|
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note: consider making it a `const` item
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--> tests/ui-toml/excessive_precision/excessive_precision.rs:12:5
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|
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LL | let _: f32 = 1.012345678901234567890;
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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= note: `-D clippy::excessive-precision` implied by `-D warnings`
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= help: to override `-D warnings` add `#[allow(clippy::excessive_precision)]`
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help: consider changing the type or truncating it to
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|
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LL - let _: f32 = 1.012345678901234567890;
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LL + let _: f32 = 1.012_345_7;
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|
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error: float has excessive precision
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--> tests/ui-toml/excessive_precision/excessive_precision.rs:14:18
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|
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LL | let _: f64 = 1.012345678901234567890;
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| ^^^^^^^^^^^^^^^^^^^^^^^
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|
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note: consider making it a `const` item
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--> tests/ui-toml/excessive_precision/excessive_precision.rs:14:5
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|
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LL | let _: f64 = 1.012345678901234567890;
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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help: consider changing the type or truncating it to
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|
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LL - let _: f64 = 1.012345678901234567890;
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LL + let _: f64 = 1.012_345_678_901_234_6;
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|
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error: aborting due to 2 previous errors
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‎tests/ui-toml/toml_unknown_key/conf_unknown_key.stderr‎

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@@ -35,6 +35,7 @@ error: error reading Clippy's configuration file: unknown field `foobar`, expect
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check-inconsistent-struct-field-initializers
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check-private-items
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cognitive-complexity-threshold
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const-literal-digits-threshold
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disallowed-macros
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disallowed-methods
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disallowed-names
@@ -129,6 +130,7 @@ error: error reading Clippy's configuration file: unknown field `barfoo`, expect
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check-inconsistent-struct-field-initializers
130131
check-private-items
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cognitive-complexity-threshold
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const-literal-digits-threshold
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disallowed-macros
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disallowed-methods
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disallowed-names
@@ -223,6 +225,7 @@ error: error reading Clippy's configuration file: unknown field `allow_mixed_uni
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check-inconsistent-struct-field-initializers
224226
check-private-items
225227
cognitive-complexity-threshold
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const-literal-digits-threshold
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disallowed-macros
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disallowed-methods
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disallowed-names

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