Auto merge of #59076 - dtolnay:comma, r=alexcrichton

Include trailing comma in multiline Debug representation This PR changes the behavior of [`Formatter::debug_struct`](https://doc.rust-lang.org/std/fmt/struct.Formatter.html#method.debug_struct), [`debug_tuple`](https://doc.rust-lang.org/std/fmt/struct.Formatter.html#method.debug_tuple), [`debug_list`](https://doc.rust-lang.org/std/fmt/struct.Formatter.html#method.debug_list), [`debug_set`](https://doc.rust-lang.org/std/fmt/struct.Formatter.html#method.debug_set), and [`debug_map`](https://doc.rust-lang.org/std/fmt/struct.Formatter.html#method.debug_map) to render trailing commas in `{:#?}` mode, which is the dominant style in modern Rust code. #### Before: ```console Language { name: "Rust", trailing_commas: false } ``` #### After: ```console Language { name: "Rust", trailing_commas: true, } ```

Author: bors

src/libcore/fmt/builders.rs

@@ -11,7 +11,7 @@ impl<'a> PadAdapter<'a> {
  fmt.wrap_buf(move |buf| {
  *slot = Some(PadAdapter {
  buf,
- on_newline: false,
+ on_newline: true,
  });
  slot.as_mut().unwrap()
  })
@@ -128,22 +128,21 @@ impl<'a, 'b: 'a> DebugStruct<'a, 'b> {
  #[stable(feature = "debug_builders", since = "1.2.0")]
  pub fn field(&mut self, name: &str, value: &dyn fmt::Debug) -> &mut DebugStruct<'a, 'b> {
  self.result = self.result.and_then(|_| {
- let prefix = if self.has_fields {
- ","
- } else {
- " {"
- };
-
  if self.is_pretty() {
+ if !self.has_fields {
+ self.fmt.write_str(" {\n")?;
+ }
  let mut slot = None;
  let mut writer = PadAdapter::wrap(&mut self.fmt, &mut slot);
- writer.write_str(prefix)?;
- writer.write_str("\n")?;
  writer.write_str(name)?;
  writer.write_str(": ")?;
- value.fmt(&mut writer)
+ value.fmt(&mut writer)?;
+ writer.write_str(",\n")
  } else {
- write!(self.fmt, "{} {}: ", prefix, name)?;
+ let prefix = if self.has_fields { ", " } else { " { " };
+ self.fmt.write_str(prefix)?;
+ self.fmt.write_str(name)?;
+ self.fmt.write_str(": ")?;
  value.fmt(self.fmt)
  }
  });
@@ -184,7 +183,7 @@ impl<'a, 'b: 'a> DebugStruct<'a, 'b> {
  if self.has_fields {
  self.result = self.result.and_then(|_| {
  if self.is_pretty() {
- self.fmt.write_str("\n}")
+ self.fmt.write_str("}")
  } else {
  self.fmt.write_str(" }")
  }
@@ -275,21 +274,17 @@ impl<'a, 'b: 'a> DebugTuple<'a, 'b> {
  #[stable(feature = "debug_builders", since = "1.2.0")]
  pub fn field(&mut self, value: &dyn fmt::Debug) -> &mut DebugTuple<'a, 'b> {
  self.result = self.result.and_then(|_| {
- let (prefix, space) = if self.fields > 0 {
- (",", " ")
- } else {
- ("(", "")
- };
-
  if self.is_pretty() {
+ if self.fields == 0 {
+ self.fmt.write_str("(\n")?;
+ }
  let mut slot = None;
  let mut writer = PadAdapter::wrap(&mut self.fmt, &mut slot);
- writer.write_str(prefix)?;
- writer.write_str("\n")?;
- value.fmt(&mut writer)
+ value.fmt(&mut writer)?;
+ writer.write_str(",\n")
  } else {
+ let prefix = if self.fields == 0 { "(" } else { ", " };
  self.fmt.write_str(prefix)?;
- self.fmt.write_str(space)?;
  value.fmt(self.fmt)
  }
  });
@@ -326,10 +321,7 @@ impl<'a, 'b: 'a> DebugTuple<'a, 'b> {
  pub fn finish(&mut self) -> fmt::Result {
  if self.fields > 0 {
  self.result = self.result.and_then(|_| {
- if self.is_pretty() {
- self.fmt.write_str("\n")?;
- }
- if self.fields == 1 && self.empty_name {
+ if self.fields == 1 && self.empty_name && !self.is_pretty() {
  self.fmt.write_str(",")?;
  }
  self.fmt.write_str(")")
@@ -353,14 +345,13 @@ impl<'a, 'b: 'a> DebugInner<'a, 'b> {
  fn entry(&mut self, entry: &dyn fmt::Debug) {
  self.result = self.result.and_then(|_| {
  if self.is_pretty() {
+ if !self.has_fields {
+ self.fmt.write_str("\n")?;
+ }
  let mut slot = None;
  let mut writer = PadAdapter::wrap(&mut self.fmt, &mut slot);
- writer.write_str(if self.has_fields {
- ",\n"
- } else {
- "\n"
- })?;
- entry.fmt(&mut writer)
+ entry.fmt(&mut writer)?;
+ writer.write_str(",\n")
  } else {
  if self.has_fields {
  self.fmt.write_str(", ")?
@@ -372,15 +363,6 @@ impl<'a, 'b: 'a> DebugInner<'a, 'b> {
  self.has_fields = true;
  }
 
- pub fn finish(&mut self) {
- let prefix = if self.is_pretty() && self.has_fields {
- "\n"
- } else {
- ""
- };
- self.result = self.result.and_then(|_| self.fmt.write_str(prefix));
- }
-
  fn is_pretty(&self) -> bool {
  self.fmt.alternate()
  }
@@ -421,7 +403,7 @@ pub struct DebugSet<'a, 'b: 'a> {
 }
 
 pub fn debug_set_new<'a, 'b>(fmt: &'a mut fmt::Formatter<'b>) -> DebugSet<'a, 'b> {
- let result = write!(fmt, "{{");
+ let result = fmt.write_str("{");
  DebugSet {
  inner: DebugInner {
  fmt,
@@ -519,7 +501,6 @@ impl<'a, 'b: 'a> DebugSet<'a, 'b> {
  /// ```
  #[stable(feature = "debug_builders", since = "1.2.0")]
  pub fn finish(&mut self) -> fmt::Result {
- self.inner.finish();
  self.inner.result.and_then(|_| self.inner.fmt.write_str("}"))
  }
 }
@@ -559,7 +540,7 @@ pub struct DebugList<'a, 'b: 'a> {
 }
 
 pub fn debug_list_new<'a, 'b>(fmt: &'a mut fmt::Formatter<'b>) -> DebugList<'a, 'b> {
- let result = write!(fmt, "[");
+ let result = fmt.write_str("[");
  DebugList {
  inner: DebugInner {
  fmt,
@@ -657,7 +638,6 @@ impl<'a, 'b: 'a> DebugList<'a, 'b> {
  /// ```
  #[stable(feature = "debug_builders", since = "1.2.0")]
  pub fn finish(&mut self) -> fmt::Result {
- self.inner.finish();
  self.inner.result.and_then(|_| self.inner.fmt.write_str("]"))
  }
 }
@@ -699,7 +679,7 @@ pub struct DebugMap<'a, 'b: 'a> {
 }
 
 pub fn debug_map_new<'a, 'b>(fmt: &'a mut fmt::Formatter<'b>) -> DebugMap<'a, 'b> {
- let result = write!(fmt, "{{");
+ let result = fmt.write_str("{");
  DebugMap {
  fmt,
  result,
@@ -734,16 +714,15 @@ impl<'a, 'b: 'a> DebugMap<'a, 'b> {
  pub fn entry(&mut self, key: &dyn fmt::Debug, value: &dyn fmt::Debug) -> &mut DebugMap<'a, 'b> {
  self.result = self.result.and_then(|_| {
  if self.is_pretty() {
+ if !self.has_fields {
+ self.fmt.write_str("\n")?;
+ }
  let mut slot = None;
  let mut writer = PadAdapter::wrap(&mut self.fmt, &mut slot);
- writer.write_str(if self.has_fields {
- ",\n"
- } else {
- "\n"
- })?;
  key.fmt(&mut writer)?;
  writer.write_str(": ")?;
- value.fmt(&mut writer)
+ value.fmt(&mut writer)?;
+ writer.write_str(",\n")
  } else {
  if self.has_fields {
  self.fmt.write_str(", ")?
@@ -818,12 +797,7 @@ impl<'a, 'b: 'a> DebugMap<'a, 'b> {
  /// ```
  #[stable(feature = "debug_builders", since = "1.2.0")]
  pub fn finish(&mut self) -> fmt::Result {
- let prefix = if self.is_pretty() && self.has_fields {
- "\n"
- } else {
- ""
- };
- self.result.and_then(|_| write!(self.fmt, "{}}}", prefix))
+ self.result.and_then(|_| self.fmt.write_str("}"))
  }
 
  fn is_pretty(&self) -> bool {

src/libcore/tests/fmt/builders.rs

@@ -30,7 +30,7 @@ mod debug_struct {
  assert_eq!("Foo { bar: true }", format!("{:?}", Foo));
  assert_eq!(
 "Foo {
- bar: true
+ bar: true,
 }",
  format!("{:#?}", Foo));
  }
@@ -52,7 +52,7 @@ mod debug_struct {
  assert_eq!(
 "Foo {
  bar: true,
- baz: 10/20
+ baz: 10/20,
 }",
  format!("{:#?}", Foo));
  }
@@ -87,9 +87,9 @@ mod debug_struct {
 "Bar {
  foo: Foo {
  bar: true,
- baz: 10/20
+ baz: 10/20,
  },
- hello: \"world\"
+ hello: \"world\",
 }",
  format!("{:#?}", Bar));
  }
@@ -127,7 +127,7 @@ mod debug_tuple {
  assert_eq!("Foo(true)", format!("{:?}", Foo));
  assert_eq!(
 "Foo(
- true
+ true,
 )",
  format!("{:#?}", Foo));
  }
@@ -149,7 +149,7 @@ mod debug_tuple {
  assert_eq!(
 "Foo(
  true,
- 10/20
+ 10/20,
 )",
  format!("{:#?}", Foo));
  }
@@ -184,9 +184,9 @@ mod debug_tuple {
 "Bar(
  Foo(
  true,
- 10/20
+ 10/20,
  ),
- \"world\"
+ \"world\",
 )",
  format!("{:#?}", Bar));
  }
@@ -224,7 +224,7 @@ mod debug_map {
  assert_eq!("{\"bar\": true}", format!("{:?}", Foo));
  assert_eq!(
 "{
- \"bar\": true
+ \"bar\": true,
 }",
  format!("{:#?}", Foo));
  }
@@ -246,7 +246,7 @@ mod debug_map {
  assert_eq!(
 "{
  \"bar\": true,
- 10: 10/20
+ 10: 10/20,
 }",
  format!("{:#?}", Foo));
  }
@@ -282,12 +282,12 @@ mod debug_map {
 "{
  \"foo\": {
  \"bar\": true,
- 10: 10/20
+ 10: 10/20,
  },
  {
  \"bar\": true,
- 10: 10/20
- }: \"world\"
+ 10: 10/20,
+ }: \"world\",
 }",
  format!("{:#?}", Bar));
  }
@@ -325,7 +325,7 @@ mod debug_set {
  assert_eq!("{true}", format!("{:?}", Foo));
  assert_eq!(
 "{
- true
+ true,
 }",
  format!("{:#?}", Foo));
  }
@@ -347,7 +347,7 @@ mod debug_set {
  assert_eq!(
 "{
  true,
- 10/20
+ 10/20,
 }",
  format!("{:#?}", Foo));
  }
@@ -382,9 +382,9 @@ mod debug_set {
 "{
  {
  true,
- 10/20
+ 10/20,
  },
- \"world\"
+ \"world\",
 }",
  format!("{:#?}", Bar));
  }
@@ -422,7 +422,7 @@ mod debug_list {
  assert_eq!("[true]", format!("{:?}", Foo));
  assert_eq!(
 "[
- true
+ true,
 ]",
  format!("{:#?}", Foo));
  }
@@ -444,7 +444,7 @@ mod debug_list {
  assert_eq!(
 "[
  true,
- 10/20
+ 10/20,
 ]",
  format!("{:#?}", Foo));
  }
@@ -479,9 +479,9 @@ mod debug_list {
 "[
  [
  true,
- 10/20
+ 10/20,
  ],
- \"world\"
+ \"world\",
 ]",
  format!("{:#?}", Bar));
  }
@@ -513,31 +513,31 @@ fn test_formatting_parameters_are_forwarded() {
  assert_eq!(format!("{:#03?}", struct_), "
 Foo {
  bar: 1024,
- baz: 007
+ baz: 007,
 }
  ".trim());
  assert_eq!(format!("{:#03?}", tuple), "
 (
  1024,
- 007
+ 007,
 )
  ".trim());
  assert_eq!(format!("{:#03?}", list), "
 [
  1024,
- 007
+ 007,
 ]
  ".trim());
  assert_eq!(format!("{:#03?}", map), r#"
 {
  "bar": 1024,
- "baz": 007
+ "baz": 007,
 }
  "#.trim());
  assert_eq!(format!("{:#03?}", set), "
 {
  007,
- 1024
+ 1024,
 }
  ".trim());
 }