Add test for variable width in USELESS_FORMAT

Author: mcarton

tests/ui/format.rs

@@ -14,6 +14,7 @@ fn main() {
     format!("{}", "foo");
     format!("{:?}", "foo"); // don't warn about debug
     format!("{:8}", "foo");
+    format!("{:width$}", "foo", width = 8);
     format!("{:+}", "foo"); // warn when the format makes no difference
     format!("{:<}", "foo"); // warn when the format makes no difference
     format!("foo {}", "bar");
@@ -23,6 +24,7 @@ fn main() {
     format!("{}", arg);
     format!("{:?}", arg); // don't warn about debug
     format!("{:8}", arg);
+    format!("{:width$}", arg, width = 8);
     format!("{:+}", arg); // warn when the format makes no difference
     format!("{:<}", arg); // warn when the format makes no difference
     format!("foo {}", arg);

tests/ui/format.stderr

@@ -15,41 +15,41 @@ error: useless use of `format!`
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
 error: useless use of `format!`
-  --> $DIR/format.rs:17:5
+  --> $DIR/format.rs:18:5
    |
-17 |     format!("{:+}", "foo"); // warn when the format makes no difference
+18 |     format!("{:+}", "foo"); // warn when the format makes no difference
    |     ^^^^^^^^^^^^^^^^^^^^^^^ help: consider using .to_string(): `"foo".to_string()`
    |
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
 error: useless use of `format!`
-  --> $DIR/format.rs:18:5
+  --> $DIR/format.rs:19:5
    |
-18 |     format!("{:<}", "foo"); // warn when the format makes no difference
+19 |     format!("{:<}", "foo"); // warn when the format makes no difference
    |     ^^^^^^^^^^^^^^^^^^^^^^^ help: consider using .to_string(): `"foo".to_string()`
    |
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
 error: useless use of `format!`
-  --> $DIR/format.rs:23:5
+  --> $DIR/format.rs:24:5
    |
-23 |     format!("{}", arg);
+24 |     format!("{}", arg);
    |     ^^^^^^^^^^^^^^^^^^^ help: consider using .to_string(): `arg.to_string()`
    |
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
 error: useless use of `format!`
-  --> $DIR/format.rs:26:5
+  --> $DIR/format.rs:28:5
    |
-26 |     format!("{:+}", arg); // warn when the format makes no difference
+28 |     format!("{:+}", arg); // warn when the format makes no difference
    |     ^^^^^^^^^^^^^^^^^^^^^ help: consider using .to_string(): `arg.to_string()`
    |
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
 error: useless use of `format!`
-  --> $DIR/format.rs:27:5
+  --> $DIR/format.rs:29:5
    |
-27 |     format!("{:<}", arg); // warn when the format makes no difference
+29 |     format!("{:<}", arg); // warn when the format makes no difference
    |     ^^^^^^^^^^^^^^^^^^^^^ help: consider using .to_string(): `arg.to_string()`
    |
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)