Reword message for incorrect float literal

Author: estebank

src/libsyntax/parse/parser.rs

@@ -2002,10 +2002,10 @@ impl<'a> Parser<'a> {
                     self.bump();
                     let sp = lo.to(self.prev_span);
                     let mut err = self.diagnostic()
-                        .struct_span_err(sp, "numeric float literals must have a significant");
+                        .struct_span_err(sp, "float literals must have an integer part");
                     err.span_suggestion_with_applicability(
                         sp,
-                        "numeric float literals must have a significant",
+                        "must have an integer part",
                         format!("0.{}", val),
                         Applicability::MachineApplicable,
                     );

src/test/ui/issues/issue-52496.rs

@@ -2,7 +2,7 @@ struct Foo { bar: f64, baz: i64, bat: i64 }
 
 fn main() {
     let _ = Foo { bar: .5, baz: 42 };
-    //~^ ERROR numeric float literals must have a significant
+    //~^ ERROR float literals must have an integer part
     //~| ERROR missing field `bat` in initializer of `Foo`
     //~| ERROR mismatched types
     let bar = 1.5f32;

src/test/ui/issues/issue-52496.stderr

@@ -1,8 +1,8 @@
-error: numeric float literals must have a significant
+error: float literals must have an integer part
   --> $DIR/issue-52496.rs:4:24
    |
 LL |     let _ = Foo { bar: .5, baz: 42 };
-   |                        ^^ help: numeric float literals must have a significant: `0.5`
+   |                        ^^ help: must have an integer part: `0.5`
 
 error: expected one of `,` or `}`, found `.`
   --> $DIR/issue-52496.rs:9:22