Correctly handle signs in exponents in numeric_literal::format()

Author: Manishearth

clippy_utils/src/numeric_literal.rs

@@ -177,6 +177,13 @@ impl<'a> NumericLiteral<'a> {
 
         let mut digits = input.chars().filter(|&c| c != '_');
 
+        // The exponent may have a sign, output it early, otherwise it will be
+        // treated as a digit
+        if let Some('-') = digits.clone().next() {
+            let _ = digits.next();
+            output.push('-');
+        }
+
         let first_group_size;
 
         if partial_group_first {

tests/ui/excessive_precision.fixed

@@ -62,5 +62,5 @@ fn main() {
     let num = 0.000_000_000_01e-10f64;
 
     // issue #7744
-    let _ = 2.225_073_858_507_201e-_308_f64;
+    let _ = 2.225_073_858_507_201e-308_f64;
 }

tests/ui/excessive_precision.stderr

@@ -82,7 +82,7 @@ error: float has excessive precision
   --> $DIR/excessive_precision.rs:65:13
    |
 LL |     let _ = 2.225_073_858_507_201_1e-308_f64;
-   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider changing the type or truncating it to: `2.225_073_858_507_201e-_308_f64`
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider changing the type or truncating it to: `2.225_073_858_507_201e-308_f64`
 
 error: aborting due to 14 previous errors