Rollup merge of #146478 - ferrocene:pvdrz/improve-fmt-coverage, r=Mark-Simulacrum

Improve `core::fmt` coverage
This PR improves the `core::fmt` coverage by adding new tests to `coretests`

Author: matthiaskrgr

library/coretests/tests/fmt/builders.rs

@@ -173,6 +173,21 @@ mod debug_struct {
  format!("{Bar:#?}")
 );
 }
+
+#[test]
+fntest_field_with(){
+structFoo;
+impl fmt::DebugforFoo{
+fnfmt(&self,fmt:&mut fmt::Formatter<'_>) -> fmt::Result{
+ fmt.debug_struct("Foo")
+.field_with("bar", |f| f.write_str("true"))
+.field_with("baz", |f| f.write_str("false"))
+.finish()
+}
+}
+
+assert_eq!("Foo {\n bar: true,\n baz: false,\n}", format!("{Foo:#?}"))
+}
 }
 
 mod debug_tuple {

library/coretests/tests/fmt/mod.rs

@@ -57,6 +57,36 @@ fn test_fmt_debug_of_raw_pointers() {
 check_fmt(vtable as*constdynDebug,"Pointer { addr: ",", metadata: DynMetadata(");
 }
 
+#[test]
+fntest_fmt_debug_of_mut_reference(){
+letmut x:u32 = 0;
+
+assert_eq!(format!("{:?}",&mut x),"0");
+}
+
+#[test]
+fntest_default_write_impls(){
+use core::fmt::Write;
+
+structBuf(String);
+
+implWriteforBuf{
+fnwrite_str(&mutself,s:&str) -> core::fmt::Result{
+self.0.write_str(s)
+}
+}
+
+letmut buf = Buf(String::new());
+ buf.write_char('a').unwrap();
+
+assert_eq!(buf.0,"a");
+
+letmut buf = Buf(String::new());
+ buf.write_fmt(format_args!("a")).unwrap();
+
+assert_eq!(buf.0,"a");
+}
+
 #[test]
 fntest_estimated_capacity(){
 assert_eq!(format_args!("").estimated_capacity(),0);

library/coretests/tests/fmt/num.rs

@@ -323,3 +323,9 @@ fn test_format_debug_hex() {
 assert_eq!(format!("{:02x?}",b"Foo\0"),"[46, 6f, 6f, 00]");
 assert_eq!(format!("{:02X?}",b"Foo\0"),"[46, 6F, 6F, 00]");
 }
+
+#[test]
+#[should_panic = "Formatting argument out of range"]
+fntest_rt_width_too_long(){
+let _ = format!("Hello {:width$}!","x", width = u16::MAXasusize + 1);
+}

library/coretests/tests/lib.rs

@@ -33,6 +33,7 @@
 #![feature(core_private_bignum)]
 #![feature(core_private_diy_float)]
 #![feature(cstr_display)]
+#![feature(debug_closure_helpers)]
 #![feature(dec2flt)]
 #![feature(drop_guard)]
 #![feature(duration_constants)]