Suppress --fmt --check diff if --quiet is passed (#1457)

src/subcommand.rs

@@ -374,6 +374,7 @@ impl Subcommand {
       return if formatted == src {
         Ok(())
       } else {
+        if !config.verbosity.quiet() {
           use similar::{ChangeTag, TextDiff};
 
           let diff = TextDiff::configure()
@@ -391,6 +392,7 @@ impl Subcommand {
               eprint!("{}{symbol}{change}{}", color.prefix(), color.suffix());
             }
           }
+        }
 
         Err(Error::FormatCheckFoundDiff)
       };

tests/fmt.rs

@@ -53,6 +53,14 @@ test! {
   status: EXIT_FAILURE,
 }
 
+test! {
+  name: check_found_diff_quiet,
+  justfile: "x:=``\n",
+  args: ("--unstable", "--fmt", "--check", "--quiet"),
+  stderr: "",
+  status: EXIT_FAILURE,
+}
+
 test! {
   name: check_diff_color,
   justfile: "x:=``\n",