Auto merge of rust-lang#7722 - dtolnay-contrib:float, r=giraffate

Stop suggesting a float truncation that is not shorter

Fixes rust-lang#7721.

Previously Clippy would say that a number has excessive precision even if it has the minimum possible precision for the floating point value that it corresponds to.

changelog: Fix [`excessive_precision`] being triggered on floats that are already written in shortest form

Author: bors

clippy_lints/src/float_literal.rs

@@ -111,7 +111,7 @@ impl<'tcx> LateLintPass<'tcx> for FloatLiteral {
                             Applicability::MachineApplicable,
                         );
                     }
-                } else if digits > max as usize && sym_str != float_str {
+                } else if digits > max as usize && float_str.len() < sym_str.len() {
                     span_lint_and_sugg(
                         cx,
                         EXCESSIVE_PRECISION,

tests/ui/excessive_precision.fixed

@@ -17,8 +17,8 @@ fn main() {
     const BAD32_3: f32 = 0.1;
     const BAD32_EDGE: f32 = 1.000_001;
 
-    const BAD64_1: f64 = 0.123_456_789_012_345_66_f64;
-    const BAD64_2: f64 = 0.123_456_789_012_345_66;
+    const BAD64_1: f64 = 0.123_456_789_012_345_67f64;
+    const BAD64_2: f64 = 0.123_456_789_012_345_67;
     const BAD64_3: f64 = 0.1;
 
     // Literal as param
@@ -37,9 +37,9 @@ fn main() {
     let bad32_suf: f32 = 1.123_456_8_f32;
     let bad32_inf = 1.123_456_8_f32;
 
-    let bad64: f64 = 0.123_456_789_012_345_66;
-    let bad64_suf: f64 = 0.123_456_789_012_345_66_f64;
-    let bad64_inf = 0.123_456_789_012_345_66;
+    let bad64: f64 = 0.123_456_789_012_345_67;
+    let bad64_suf: f64 = 0.123_456_789_012_345_67f64;
+    let bad64_inf = 0.123_456_789_012_345_67;
 
     // Vectors
     let good_vec32: Vec<f32> = vec![0.123_456];

tests/ui/excessive_precision.stderr

@@ -24,18 +24,6 @@ error: float has excessive precision
 LL |     const BAD32_EDGE: f32 = 1.000_000_9;
    |                             ^^^^^^^^^^^ help: consider changing the type or truncating it to: `1.000_001`
 
-error: float has excessive precision
-  --> $DIR/excessive_precision.rs:20:26
-   |
-LL |     const BAD64_1: f64 = 0.123_456_789_012_345_67f64;
-   |                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider changing the type or truncating it to: `0.123_456_789_012_345_66_f64`
-
-error: float has excessive precision
-  --> $DIR/excessive_precision.rs:21:26
-   |
-LL |     const BAD64_2: f64 = 0.123_456_789_012_345_67;
-   |                          ^^^^^^^^^^^^^^^^^^^^^^^^ help: consider changing the type or truncating it to: `0.123_456_789_012_345_66`
-
 error: float has excessive precision
   --> $DIR/excessive_precision.rs:22:26
    |
@@ -66,24 +54,6 @@ error: float has excessive precision
 LL |     let bad32_inf = 1.123_456_789_f32;
    |                     ^^^^^^^^^^^^^^^^^ help: consider changing the type or truncating it to: `1.123_456_8_f32`
 
-error: float has excessive precision
-  --> $DIR/excessive_precision.rs:40:22
-   |
-LL |     let bad64: f64 = 0.123_456_789_012_345_67;
-   |                      ^^^^^^^^^^^^^^^^^^^^^^^^ help: consider changing the type or truncating it to: `0.123_456_789_012_345_66`
-
-error: float has excessive precision
-  --> $DIR/excessive_precision.rs:41:26
-   |
-LL |     let bad64_suf: f64 = 0.123_456_789_012_345_67f64;
-   |                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider changing the type or truncating it to: `0.123_456_789_012_345_66_f64`
-
-error: float has excessive precision
-  --> $DIR/excessive_precision.rs:42:21
-   |
-LL |     let bad64_inf = 0.123_456_789_012_345_67;
-   |                     ^^^^^^^^^^^^^^^^^^^^^^^^ help: consider changing the type or truncating it to: `0.123_456_789_012_345_66`
-
 error: float has excessive precision
   --> $DIR/excessive_precision.rs:48:36
    |
@@ -108,5 +78,5 @@ 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: aborting due to 18 previous errors
+error: aborting due to 13 previous errors