Auto merge of #5202 - krishna-veerareddy:issue-5201-move-lossy-float-…

…literal-restriction, r=flip1995 Move check for lossy whole-number floats out of `excessive_precision` changelog: Add new lint `lossy_float_literal` to detect lossy whole number float literals and move it out of `excessive_precision` again. Fixes #5201
rust-lang · Feb 21, 2020 · f8ea194 · f8ea194
2 parents 8fbb23f + 219c94d
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -1207,6 +1207,7 @@ Released 2018-09-13
 [`let_unit_value`]: https://rust-lang.github.io/rust-clippy/master/index.html#let_unit_value
 [`linkedlist`]: https://rust-lang.github.io/rust-clippy/master/index.html#linkedlist
 [`logic_bug`]: https://rust-lang.github.io/rust-clippy/master/index.html#logic_bug
+[`lossy_float_literal`]: https://rust-lang.github.io/rust-clippy/master/index.html#lossy_float_literal
 [`main_recursion`]: https://rust-lang.github.io/rust-clippy/master/index.html#main_recursion
 [`manual_memcpy`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_memcpy
 [`manual_mul_add`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_mul_add

diff --git a/README.md b/README.md
@@ -5,7 +5,7 @@
 
 A collection of lints to catch common mistakes and improve your [Rust](https://github.com/rust-lang/rust) code.
 
-[There are 355 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
+[There are 356 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
 
 We have a bunch of lint categories to allow you to choose how much Clippy is supposed to ~~annoy~~ help you:
 

diff --git a/clippy_lints/src/excessive_precision.rs → clippy_lints/src/float_literal.rs b/clippy_lints/src/excessive_precision.rs → clippy_lints/src/float_literal.rs
@@ -13,30 +13,53 @@ declare_clippy_lint! {
     /// **What it does:** Checks for float literals with a precision greater
     /// than that supported by the underlying type.
     ///
-    /// **Why is this bad?** Rust will silently lose precision during conversion
-    /// to a float.
+    /// **Why is this bad?** Rust will truncate the literal silently.
     ///
     /// **Known problems:** None.
     ///
     /// **Example:**
     ///
     /// ```rust
     /// // Bad
-    /// let a: f32 = 0.123_456_789_9; // 0.123_456_789
-    /// let b: f32 = 16_777_217.0; // 16_777_216.0
+    /// let v: f32 = 0.123_456_789_9;
+    /// println!("{}", v); //  0.123_456_789
     ///
     /// // Good
-    /// let a: f64 = 0.123_456_789_9;
-    /// let b: f64 = 16_777_216.0;
+    /// let v: f64 = 0.123_456_789_9;
+    /// println!("{}", v); //  0.123_456_789_9
     /// ```
     pub EXCESSIVE_PRECISION,
-    correctness,
+    style,
     "excessive precision for float literal"
 }
 
-declare_lint_pass!(ExcessivePrecision => [EXCESSIVE_PRECISION]);
+declare_clippy_lint! {
+    /// **What it does:** Checks for whole number float literals that
+    /// cannot be represented as the underlying type without loss.
+    ///
+    /// **Why is this bad?** Rust will silently lose precision during
+    /// conversion to a float.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    ///
+    /// ```rust
+    /// // Bad
+    /// let _: f32 = 16_777_217.0; // 16_777_216.0
+    ///
+    /// // Good
+    /// let _: f32 = 16_777_216.0;
+    /// let _: f64 = 16_777_217.0;
+    /// ```
+    pub LOSSY_FLOAT_LITERAL,
+    restriction,
+    "lossy whole number float literals"
+}
+
+declare_lint_pass!(FloatLiteral => [EXCESSIVE_PRECISION, LOSSY_FLOAT_LITERAL]);
 
-impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ExcessivePrecision {
+impl<'a, 'tcx> LateLintPass<'a, 'tcx> for FloatLiteral {
     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr<'_>) {
         if_chain! {
             let ty = cx.tables.expr_ty(expr);
@@ -52,26 +75,41 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ExcessivePrecision {
                 // since we'll need the truncated string anyway.
                 let digits = count_digits(&sym_str);
                 let max = max_digits(fty);
-                let float_str = match fty {
-                    FloatTy::F32 => sym_str.parse::<f32>().map(|f| formatter.format(f)),
-                    FloatTy::F64 => sym_str.parse::<f64>().map(|f| formatter.format(f)),
-                }.unwrap();
                 let type_suffix = match lit_float_ty {
                     LitFloatType::Suffixed(FloatTy::F32) => Some("f32"),
                     LitFloatType::Suffixed(FloatTy::F64) => Some("f64"),
                     _ => None
                 };
+                let (is_whole, mut float_str) = match fty {
+                    FloatTy::F32 => {
+                        let value = sym_str.parse::<f32>().unwrap();
+
+                        (value.fract() == 0.0, formatter.format(value))
+                    },
+                    FloatTy::F64 => {
+                        let value = sym_str.parse::<f64>().unwrap();
+
+                        (value.fract() == 0.0, formatter.format(value))
+                    },
+                };
 
-                if is_whole_number(&sym_str, fty) {
+                if is_whole && !sym_str.contains(|c| c == 'e' || c == 'E') {
                     // Normalize the literal by stripping the fractional portion
                     if sym_str.split('.').next().unwrap() != float_str {
+                        // If the type suffix is missing the suggestion would be
+                        // incorrectly interpreted as an integer so adding a `.0`
+                        // suffix to prevent that.
+                        if type_suffix.is_none() {
+                            float_str.push_str(".0");
+                        }
+
                         span_lint_and_sugg(
                             cx,
-                            EXCESSIVE_PRECISION,
+                            LOSSY_FLOAT_LITERAL,
                             expr.span,
                             "literal cannot be represented as the underlying type without loss of precision",
                             "consider changing the type or replacing it with",
-                            format_numeric_literal(format!("{}.0", float_str).as_str(), type_suffix, true),
+                            format_numeric_literal(&float_str, type_suffix, true),
                             Applicability::MachineApplicable,
                         );
                     }
@@ -91,15 +129,6 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ExcessivePrecision {
     }
 }
 
-// Checks whether a float literal is a whole number
-#[must_use]
-fn is_whole_number(sym_str: &str, fty: FloatTy) -> bool {
-    match fty {
-        FloatTy::F32 => sym_str.parse::<f32>().unwrap().fract() == 0.0,
-        FloatTy::F64 => sym_str.parse::<f64>().unwrap().fract() == 0.0,
-    }
-}
-
 #[must_use]
 fn max_digits(fty: FloatTy) -> u32 {
     match fty {

diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs
@@ -205,10 +205,10 @@ pub mod escape;
 pub mod eta_reduction;
 pub mod eval_order_dependence;
 pub mod excessive_bools;
-pub mod excessive_precision;
 pub mod exit;
 pub mod explicit_write;
 pub mod fallible_impl_from;
+pub mod float_literal;
 pub mod format;
 pub mod formatting;
 pub mod functions;
@@ -534,10 +534,11 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         &eval_order_dependence::EVAL_ORDER_DEPENDENCE,
         &excessive_bools::FN_PARAMS_EXCESSIVE_BOOLS,
         &excessive_bools::STRUCT_EXCESSIVE_BOOLS,
-        &excessive_precision::EXCESSIVE_PRECISION,
         &exit::EXIT,
         &explicit_write::EXPLICIT_WRITE,
         &fallible_impl_from::FALLIBLE_IMPL_FROM,
+        &float_literal::EXCESSIVE_PRECISION,
+        &float_literal::LOSSY_FLOAT_LITERAL,
         &format::USELESS_FORMAT,
         &formatting::POSSIBLE_MISSING_COMMA,
         &formatting::SUSPICIOUS_ASSIGNMENT_FORMATTING,
@@ -836,7 +837,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     store.register_late_pass(|| box eq_op::EqOp);
     store.register_late_pass(|| box enum_glob_use::EnumGlobUse);
     store.register_late_pass(|| box enum_clike::UnportableVariant);
-    store.register_late_pass(|| box excessive_precision::ExcessivePrecision);
+    store.register_late_pass(|| box float_literal::FloatLiteral);
     let verbose_bit_mask_threshold = conf.verbose_bit_mask_threshold;
     store.register_late_pass(move || box bit_mask::BitMask::new(verbose_bit_mask_threshold));
     store.register_late_pass(|| box ptr::Ptr);
@@ -1016,6 +1017,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&dbg_macro::DBG_MACRO),
         LintId::of(&else_if_without_else::ELSE_IF_WITHOUT_ELSE),
         LintId::of(&exit::EXIT),
+        LintId::of(&float_literal::LOSSY_FLOAT_LITERAL),
         LintId::of(&implicit_return::IMPLICIT_RETURN),
         LintId::of(&indexing_slicing::INDEXING_SLICING),
         LintId::of(&inherent_impl::MULTIPLE_INHERENT_IMPL),
@@ -1160,8 +1162,8 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&eta_reduction::REDUNDANT_CLOSURE),
         LintId::of(&eval_order_dependence::DIVERGING_SUB_EXPRESSION),
         LintId::of(&eval_order_dependence::EVAL_ORDER_DEPENDENCE),
-        LintId::of(&excessive_precision::EXCESSIVE_PRECISION),
         LintId::of(&explicit_write::EXPLICIT_WRITE),
+        LintId::of(&float_literal::EXCESSIVE_PRECISION),
         LintId::of(&format::USELESS_FORMAT),
         LintId::of(&formatting::POSSIBLE_MISSING_COMMA),
         LintId::of(&formatting::SUSPICIOUS_ASSIGNMENT_FORMATTING),
@@ -1386,6 +1388,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&enum_variants::MODULE_INCEPTION),
         LintId::of(&eq_op::OP_REF),
         LintId::of(&eta_reduction::REDUNDANT_CLOSURE),
+        LintId::of(&float_literal::EXCESSIVE_PRECISION),
         LintId::of(&formatting::SUSPICIOUS_ASSIGNMENT_FORMATTING),
         LintId::of(&formatting::SUSPICIOUS_ELSE_FORMATTING),
         LintId::of(&formatting::SUSPICIOUS_UNARY_OP_FORMATTING),
@@ -1565,7 +1568,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&enum_clike::ENUM_CLIKE_UNPORTABLE_VARIANT),
         LintId::of(&eq_op::EQ_OP),
         LintId::of(&erasing_op::ERASING_OP),
-        LintId::of(&excessive_precision::EXCESSIVE_PRECISION),
         LintId::of(&formatting::POSSIBLE_MISSING_COMMA),
         LintId::of(&functions::NOT_UNSAFE_PTR_ARG_DEREF),
         LintId::of(&indexing_slicing::OUT_OF_BOUNDS_INDEXING),

diff --git a/src/lintlist/mod.rs b/src/lintlist/mod.rs
@@ -6,7 +6,7 @@ pub use lint::Lint;
 pub use lint::LINT_LEVELS;
 
 // begin lint list, do not remove this comment, it’s used in `update_lints`
-pub const ALL_LINTS: [Lint; 355] = [
+pub const ALL_LINTS: [Lint; 356] = [
     Lint {
         name: "absurd_extreme_comparisons",
         group: "correctness",
@@ -492,10 +492,10 @@ pub const ALL_LINTS: [Lint; 355] = [
     },
     Lint {
         name: "excessive_precision",
-        group: "correctness",
+        group: "style",
         desc: "excessive precision for float literal",
         deprecation: None,
-        module: "excessive_precision",
+        module: "float_literal",
     },
     Lint {
         name: "exit",
@@ -1001,6 +1001,13 @@ pub const ALL_LINTS: [Lint; 355] = [
         deprecation: None,
         module: "booleans",
     },
+    Lint {
+        name: "lossy_float_literal",
+        group: "restriction",
+        desc: "lossy whole number float literals",
+        deprecation: None,
+        module: "float_literal",
+    },
     Lint {
         name: "main_recursion",
         group: "style",

diff --git a/tests/ui/excessive_precision.fixed b/tests/ui/excessive_precision.fixed
@@ -60,26 +60,4 @@ fn main() {
 
     // issue #2840
     let num = 0.000_000_000_01e-10f64;
-
-    // Lossy whole-number float literals
-    let _: f32 = 16_777_216.0;
-    let _: f32 = 16_777_220.0;
-    let _: f32 = 16_777_220.0;
-    let _: f32 = 16_777_220.0;
-    let _ = 16_777_220.0_f32;
-    let _: f32 = -16_777_220.0;
-    let _: f64 = 9_007_199_254_740_992.0;
-    let _: f64 = 9_007_199_254_740_992.0;
-    let _: f64 = 9_007_199_254_740_992.0;
-    let _ = 9_007_199_254_740_992.0_f64;
-    let _: f64 = -9_007_199_254_740_992.0;
-
-    // Lossless whole number float literals
-    let _: f32 = 16_777_216.0;
-    let _: f32 = 16_777_218.0;
-    let _: f32 = 16_777_220.0;
-    let _: f32 = -16_777_216.0;
-    let _: f32 = -16_777_220.0;
-    let _: f64 = 9_007_199_254_740_992.0;
-    let _: f64 = -9_007_199_254_740_992.0;
 }
diff --git a/tests/ui/excessive_precision.rs b/tests/ui/excessive_precision.rs
@@ -60,26 +60,4 @@ fn main() {
 
     // issue #2840
     let num = 0.000_000_000_01e-10f64;
-
-    // Lossy whole-number float literals
-    let _: f32 = 16_777_217.0;
-    let _: f32 = 16_777_219.0;
-    let _: f32 = 16_777_219.;
-    let _: f32 = 16_777_219.000;
-    let _ = 16_777_219f32;
-    let _: f32 = -16_777_219.0;
-    let _: f64 = 9_007_199_254_740_993.0;
-    let _: f64 = 9_007_199_254_740_993.;
-    let _: f64 = 9_007_199_254_740_993.000;
-    let _ = 9_007_199_254_740_993f64;
-    let _: f64 = -9_007_199_254_740_993.0;
-
-    // Lossless whole number float literals
-    let _: f32 = 16_777_216.0;
-    let _: f32 = 16_777_218.0;
-    let _: f32 = 16_777_220.0;
-    let _: f32 = -16_777_216.0;
-    let _: f32 = -16_777_220.0;
-    let _: f64 = 9_007_199_254_740_992.0;
-    let _: f64 = -9_007_199_254_740_992.0;
 }
diff --git a/tests/ui/excessive_precision.stderr b/tests/ui/excessive_precision.stderr
@@ -108,71 +108,5 @@ error: float has excessive precision
 LL |     let bad_bige32: f32 = 1.123_456_788_888E-10;
    |                           ^^^^^^^^^^^^^^^^^^^^^ help: consider changing the type or truncating it to: `1.123_456_8E-10`
 
-error: literal cannot be represented as the underlying type without loss of precision
-  --> $DIR/excessive_precision.rs:65:18
-   |
-LL |     let _: f32 = 16_777_217.0;
-   |                  ^^^^^^^^^^^^ help: consider changing the type or replacing it with: `16_777_216.0`
-
-error: literal cannot be represented as the underlying type without loss of precision
-  --> $DIR/excessive_precision.rs:66:18
-   |
-LL |     let _: f32 = 16_777_219.0;
-   |                  ^^^^^^^^^^^^ help: consider changing the type or replacing it with: `16_777_220.0`
-
-error: literal cannot be represented as the underlying type without loss of precision
-  --> $DIR/excessive_precision.rs:67:18
-   |
-LL |     let _: f32 = 16_777_219.;
-   |                  ^^^^^^^^^^^ help: consider changing the type or replacing it with: `16_777_220.0`
-
-error: literal cannot be represented as the underlying type without loss of precision
-  --> $DIR/excessive_precision.rs:68:18
-   |
-LL |     let _: f32 = 16_777_219.000;
-   |                  ^^^^^^^^^^^^^^ help: consider changing the type or replacing it with: `16_777_220.0`
-
-error: literal cannot be represented as the underlying type without loss of precision
-  --> $DIR/excessive_precision.rs:69:13
-   |
-LL |     let _ = 16_777_219f32;
-   |             ^^^^^^^^^^^^^ help: consider changing the type or replacing it with: `16_777_220.0_f32`
-
-error: literal cannot be represented as the underlying type without loss of precision
-  --> $DIR/excessive_precision.rs:70:19
-   |
-LL |     let _: f32 = -16_777_219.0;
-   |                   ^^^^^^^^^^^^ help: consider changing the type or replacing it with: `16_777_220.0`
-
-error: literal cannot be represented as the underlying type without loss of precision
-  --> $DIR/excessive_precision.rs:71:18
-   |
-LL |     let _: f64 = 9_007_199_254_740_993.0;
-   |                  ^^^^^^^^^^^^^^^^^^^^^^^ help: consider changing the type or replacing it with: `9_007_199_254_740_992.0`
-
-error: literal cannot be represented as the underlying type without loss of precision
-  --> $DIR/excessive_precision.rs:72:18
-   |
-LL |     let _: f64 = 9_007_199_254_740_993.;
-   |                  ^^^^^^^^^^^^^^^^^^^^^^ help: consider changing the type or replacing it with: `9_007_199_254_740_992.0`
-
-error: literal cannot be represented as the underlying type without loss of precision
-  --> $DIR/excessive_precision.rs:73:18
-   |
-LL |     let _: f64 = 9_007_199_254_740_993.000;
-   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider changing the type or replacing it with: `9_007_199_254_740_992.0`
-
-error: literal cannot be represented as the underlying type without loss of precision
-  --> $DIR/excessive_precision.rs:74:13
-   |
-LL |     let _ = 9_007_199_254_740_993f64;
-   |             ^^^^^^^^^^^^^^^^^^^^^^^^ help: consider changing the type or replacing it with: `9_007_199_254_740_992.0_f64`
-
-error: literal cannot be represented as the underlying type without loss of precision
-  --> $DIR/excessive_precision.rs:75:19
-   |
-LL |     let _: f64 = -9_007_199_254_740_993.0;
-   |                   ^^^^^^^^^^^^^^^^^^^^^^^ help: consider changing the type or replacing it with: `9_007_199_254_740_992.0`
-
-error: aborting due to 29 previous errors
+error: aborting due to 18 previous errors