excessive_precision: Fix false positive when exponent has leading zero (#14824)

Fixes #6341.

changelog: [`excessive_precision`] no longer triggers on an exponent
with leading zeros

Author: samueltardieu

clippy_lints/src/float_literal.rs

@@ -126,7 +126,7 @@ impl<'tcx> LateLintPass<'tcx> for FloatLiteral {
                         },
                     );
                 }
-            } else if digits > max as usize && float_str.len() < sym_str.len() {
+            } else if digits > max as usize && count_digits(&float_str) < count_digits(sym_str) {
                 span_lint_and_then(
                     cx,
                     EXCESSIVE_PRECISION,

tests/ui/excessive_precision.fixed

@@ -79,6 +79,9 @@ fn main() {
     // issue #2840
     let num = 0.000_000_000_01e-10f64;
 
+    // issue #6341
+    let exponential: f64 = 4.886506780521244E-03;
+
     // issue #7744
     let _ = 2.225_073_858_507_201e-308_f64;
     //~^ excessive_precision

tests/ui/excessive_precision.rs

@@ -79,6 +79,9 @@ fn main() {
     // issue #2840
     let num = 0.000_000_000_01e-10f64;
 
+    // issue #6341
+    let exponential: f64 = 4.886506780521244E-03;
+
     // issue #7744
     let _ = 2.225_073_858_507_201_1e-308_f64;
     //~^ excessive_precision

tests/ui/excessive_precision.stderr

@@ -157,7 +157,7 @@ LL +     let bad_bige32: f32 = 1.123_456_8E-10;
    |
 
 error: float has excessive precision
-  --> tests/ui/excessive_precision.rs:83:13
+  --> tests/ui/excessive_precision.rs:86:13
    |
 LL |     let _ = 2.225_073_858_507_201_1e-308_f64;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -169,7 +169,7 @@ LL +     let _ = 2.225_073_858_507_201e-308_f64;
    |
 
 error: float has excessive precision
-  --> tests/ui/excessive_precision.rs:87:13
+  --> tests/ui/excessive_precision.rs:90:13
    |
 LL |     let _ = 1.000_000_000_000_001e-324_f64;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -181,7 +181,7 @@ LL +     let _ = 0_f64;
    |
 
 error: float has excessive precision
-  --> tests/ui/excessive_precision.rs:98:20
+  --> tests/ui/excessive_precision.rs:101:20
    |
 LL |     const _: f64 = 3.0000000000000000e+00;
    |                    ^^^^^^^^^^^^^^^^^^^^^^