Auto merge of #23810 - sfackler:debug-collections, r=alexcrichton

The collections debug helpers no longer prefix output with the
collection name, in line with the current conventions for Debug
implementations. Implementations that want to preserve the current
behavior can simply add a `try!(write!(fmt, "TypeName "));` at the
beginning of the `fmt` method.

[breaking-change]

2 files changed, 125 insertions, 90 deletions

diff --git a/src/libcore/fmt/builders.rs b/src/libcore/fmt/builders.rs
index 07f029cc15e..f61a7f2d30c 100644
--- a/src/libcore/fmt/builders.rs
+++ b/src/libcore/fmt/builders.rs
@@ -177,22 +177,54 @@ impl<'a, 'b: 'a> DebugTuple<'a, 'b> {
     }
 }
 
+struct DebugInner<'a, 'b: 'a> {
+    fmt: &'a mut fmt::Formatter<'b>,
+    result: fmt::Result,
+    has_fields: bool,
+}
+
+impl<'a, 'b: 'a> DebugInner<'a, 'b> {
+    fn entry(&mut self, entry: &fmt::Debug) {
+        self.result = self.result.and_then(|_| {
+            if self.is_pretty() {
+                let mut writer = PadAdapter::new(self.fmt);
+                let prefix = if self.has_fields { "," } else { "" };
+                fmt::write(&mut writer, format_args!("{}\n{:#?}", prefix, entry))
+            } else {
+                let prefix = if self.has_fields { ", " } else { "" };
+                write!(self.fmt, "{}{:?}", prefix, entry)
+            }
+        });
+
+        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.flags() & (1 << (FlagV1::Alternate as usize)) != 0
+    }
+}
+
 /// A struct to help with `fmt::Debug` implementations.
 ///
 /// Constructed by the `Formatter::debug_set` method.
 #[must_use]
 pub struct DebugSet<'a, 'b: 'a> {
-    fmt: &'a mut fmt::Formatter<'b>,
-    result: fmt::Result,
-    has_fields: bool,
+    inner: DebugInner<'a, 'b>,
 }
 
-pub fn debug_set_new<'a, 'b>(fmt: &'a mut fmt::Formatter<'b>, name: &str) -> DebugSet<'a, 'b> {
-    let result = write!(fmt, "{} {{", name);
+pub fn debug_set_new<'a, 'b>(fmt: &'a mut fmt::Formatter<'b>) -> DebugSet<'a, 'b> {
+    let result = write!(fmt, "{{");
     DebugSet {
-        fmt: fmt,
-        result: result,
-        has_fields: false,
+        inner: DebugInner {
+            fmt: fmt,
+            result: result,
+            has_fields: false,
+        }
     }
 }
 
@@ -200,41 +232,52 @@ impl<'a, 'b: 'a> DebugSet<'a, 'b> {
     /// Adds a new entry to the set output.
     #[unstable(feature = "debug_builders", reason = "method was just created")]
     pub fn entry(mut self, entry: &fmt::Debug) -> DebugSet<'a, 'b> {
-        self.result = self.result.and_then(|_| {
-            let prefix = if self.has_fields {
-                ","
-            } else {
-                ""
-            };
-
-            if self.is_pretty() {
-                let mut writer = PadAdapter::new(self.fmt);
-                fmt::write(&mut writer, format_args!("{}\n{:#?}", prefix, entry))
-            } else {
-                write!(self.fmt, "{} {:?}", prefix, entry)
-            }
-        });
-
-        self.has_fields = true;
+        self.inner.entry(entry);
         self
     }
 
     /// Consumes the `DebugSet`, finishing output and returning any error
     /// encountered.
     #[unstable(feature = "debug_builders", reason = "method was just created")]
-    pub fn finish(self) -> fmt::Result {
-        self.result.and_then(|_| {
-            let end = match (self.has_fields, self.is_pretty()) {
-                (false, _) => "}",
-                (true, false) => " }",
-                (true, true) => "\n}",
-            };
-            self.fmt.write_str(end)
-        })
+    pub fn finish(mut self) -> fmt::Result {
+        self.inner.finish();
+        self.inner.result.and_then(|_| self.inner.fmt.write_str("}"))
     }
+}
 
-    fn is_pretty(&self) -> bool {
-        self.fmt.flags() & (1 << (FlagV1::Alternate as usize)) != 0
+/// A struct to help with `fmt::Debug` implementations.
+///
+/// Constructed by the `Formatter::debug_list` method.
+#[must_use]
+pub struct DebugList<'a, 'b: 'a> {
+    inner: DebugInner<'a, 'b>,
+}
+
+pub fn debug_list_new<'a, 'b>(fmt: &'a mut fmt::Formatter<'b>) -> DebugList<'a, 'b> {
+    let result = write!(fmt, "[");
+    DebugList {
+        inner: DebugInner {
+            fmt: fmt,
+            result: result,
+            has_fields: false,
+        }
+    }
+}
+
+impl<'a, 'b: 'a> DebugList<'a, 'b> {
+    /// Adds a new entry to the set output.
+    #[unstable(feature = "debug_builders", reason = "method was just created")]
+    pub fn entry(mut self, entry: &fmt::Debug) -> DebugList<'a, 'b> {
+        self.inner.entry(entry);
+        self
+    }
+
+    /// Consumes the `DebugSet`, finishing output and returning any error
+    /// encountered.
+    #[unstable(feature = "debug_builders", reason = "method was just created")]
+    pub fn finish(mut self) -> fmt::Result {
+        self.inner.finish();
+        self.inner.result.and_then(|_| self.inner.fmt.write_str("]"))
     }
 }
 
@@ -248,8 +291,8 @@ pub struct DebugMap<'a, 'b: 'a> {
     has_fields: bool,
 }
 
-pub fn debug_map_new<'a, 'b>(fmt: &'a mut fmt::Formatter<'b>, name: &str) -> DebugMap<'a, 'b> {
-    let result = write!(fmt, "{} {{", name);
+pub fn debug_map_new<'a, 'b>(fmt: &'a mut fmt::Formatter<'b>) -> DebugMap<'a, 'b> {
+    let result = write!(fmt, "{{");
     DebugMap {
         fmt: fmt,
         result: result,
@@ -262,22 +305,17 @@ impl<'a, 'b: 'a> DebugMap<'a, 'b> {
     #[unstable(feature = "debug_builders", reason = "method was just created")]
     pub fn entry(mut self, key: &fmt::Debug, value: &fmt::Debug) -> DebugMap<'a, 'b> {
         self.result = self.result.and_then(|_| {
-            let prefix = if self.has_fields {
-                ","
-            } else {
-                ""
-            };
-
             if self.is_pretty() {
                 let mut writer = PadAdapter::new(self.fmt);
+                let prefix = if self.has_fields { "," } else { "" };
                 fmt::write(&mut writer, format_args!("{}\n{:#?}: {:#?}", prefix, key, value))
             } else {
-                write!(self.fmt, "{} {:?}: {:?}", prefix, key, value)
+                let prefix = if self.has_fields { ", " } else { "" };
+                write!(self.fmt, "{}{:?}: {:?}", prefix, key, value)
             }
         });
 
         self.has_fields = true;
-
         self
     }
 
@@ -285,14 +323,8 @@ impl<'a, 'b: 'a> DebugMap<'a, 'b> {
     /// encountered.
     #[unstable(feature = "debug_builders", reason = "method was just created")]
     pub fn finish(self) -> fmt::Result {
-        self.result.and_then(|_| {
-            let end = match (self.has_fields, self.is_pretty()) {
-                (false, _) => "}",
-                (true, false) => " }",
-                (true, true) => "\n}",
-            };
-            self.fmt.write_str(end)
-        })
+        let prefix = if self.is_pretty() && self.has_fields { "\n" } else { "" };
+        self.result.and_then(|_| write!(self.fmt, "{}}}", prefix))
     }
 
     fn is_pretty(&self) -> bool {
diff --git a/src/libcore/fmt/mod.rs b/src/libcore/fmt/mod.rs
index a3de23bd7f3..ffb358cdac8 100644
--- a/src/libcore/fmt/mod.rs
+++ b/src/libcore/fmt/mod.rs
@@ -32,7 +32,7 @@ pub use self::num::radix;
 pub use self::num::Radix;
 pub use self::num::RadixFmt;
 
-pub use self::builders::{DebugStruct, DebugTuple, DebugSet, DebugMap};
+pub use self::builders::{DebugStruct, DebugTuple, DebugSet, DebugList, DebugMap};
 
 mod num;
 mod float;
@@ -644,7 +644,7 @@ impl<'a> Formatter<'a> {
     /// // prints "Foo { bar: 10, baz: "Hello World" }"
     /// println!("{:?}", Foo { bar: 10, baz: "Hello World".to_string() });
     /// ```
-    #[unstable(feature = "core", reason = "method was just created")]
+    #[unstable(feature = "debug_builders", reason = "method was just created")]
     #[inline]
     pub fn debug_struct<'b>(&'b mut self, name: &str) -> DebugStruct<'b, 'a> {
         builders::debug_struct_new(self, name)
@@ -673,12 +673,38 @@ impl<'a> Formatter<'a> {
     /// // prints "Foo(10, "Hello World")"
     /// println!("{:?}", Foo(10, "Hello World".to_string()));
     /// ```
-    #[unstable(feature = "core", reason = "method was just created")]
+    #[unstable(feature = "debug_builders", reason = "method was just created")]
     #[inline]
     pub fn debug_tuple<'b>(&'b mut self, name: &str) -> DebugTuple<'b, 'a> {
         builders::debug_tuple_new(self, name)
     }
 
+    /// Creates a `DebugList` builder designed to assist with creation of
+    /// `fmt::Debug` implementations for list-like structures.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// # #![feature(debug_builders, core)]
+    /// use std::fmt;
+    ///
+    /// struct Foo(Vec<i32>);
+    ///
+    /// impl fmt::Debug for Foo {
+    ///     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+    ///         self.0.iter().fold(fmt.debug_list(), |b, e| b.entry(e)).finish()
+    ///     }
+    /// }
+    ///
+    /// // prints "[10, 11]"
+    /// println!("{:?}", Foo(vec![10, 11]));
+    /// ```
+    #[unstable(feature = "debug_builders", reason = "method was just created")]
+    #[inline]
+    pub fn debug_list<'b>(&'b mut self) -> DebugList<'b, 'a> {
+        builders::debug_list_new(self)
+    }
+
     /// Creates a `DebugSet` builder designed to assist with creation of
     /// `fmt::Debug` implementations for set-like structures.
     ///
@@ -692,21 +718,17 @@ impl<'a> Formatter<'a> {
     ///
     /// impl fmt::Debug for Foo {
     ///     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
-    ///         let mut builder = fmt.debug_set("Foo");
-    ///         for i in &self.0 {
-    ///             builder = builder.entry(i);
-    ///         }
-    ///         builder.finish()
+    ///         self.0.iter().fold(fmt.debug_set(), |b, e| b.entry(e)).finish()
     ///     }
     /// }
     ///
-    /// // prints "Foo { 10, 11 }"
+    /// // prints "{10, 11}"
     /// println!("{:?}", Foo(vec![10, 11]));
     /// ```
-    #[unstable(feature = "core", reason = "method was just created")]
+    #[unstable(feature = "debug_builders", reason = "method was just created")]
     #[inline]
-    pub fn debug_set<'b>(&'b mut self, name: &str) -> DebugSet<'b, 'a> {
-        builders::debug_set_new(self, name)
+    pub fn debug_set<'b>(&'b mut self) -> DebugSet<'b, 'a> {
+        builders::debug_set_new(self)
     }
 
     /// Creates a `DebugMap` builder designed to assist with creation of
@@ -722,21 +744,17 @@ impl<'a> Formatter<'a> {
     ///
     /// impl fmt::Debug for Foo {
     ///     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
-    ///         let mut builder = fmt.debug_map("Foo");
-    ///         for &(ref key, ref value) in &self.0 {
-    ///             builder = builder.entry(key, value);
-    ///         }
-    ///         builder.finish()
+    ///         self.0.iter().fold(fmt.debug_map(), |b, &(ref k, ref v)| b.entry(k, v)).finish()
     ///     }
     /// }
     ///
-    /// // prints "Foo { "A": 10, "B": 11 }"
+    /// // prints "{"A": 10, "B": 11}"
     /// println!("{:?}", Foo(vec![("A".to_string(), 10), ("B".to_string(), 11)]));
     /// ```
-    #[unstable(feature = "core", reason = "method was just created")]
+    #[unstable(feature = "debug_builders", reason = "method was just created")]
     #[inline]
-    pub fn debug_map<'b>(&'b mut self, name: &str) -> DebugMap<'b, 'a> {
-        builders::debug_map_new(self, name)
+    pub fn debug_map<'b>(&'b mut self) -> DebugMap<'b, 'a> {
+        builders::debug_map_new(self)
     }
 }
 
@@ -987,22 +1005,7 @@ impl<'a> Debug for &'a (any::Any+'a) {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Debug> Debug for [T] {
     fn fmt(&self, f: &mut Formatter) -> Result {
-        if f.flags & (1 << (FlagV1::Alternate as u32)) == 0 {
-            try!(write!(f, "["));
-        }
-        let mut is_first = true;
-        for x in self {
-            if is_first {
-                is_first = false;
-            } else {
-                try!(write!(f, ", "));
-            }
-            try!(write!(f, "{:?}", *x))
-        }
-        if f.flags & (1 << (FlagV1::Alternate as u32)) == 0 {
-            try!(write!(f, "]"));
-        }
-        Ok(())
+        self.iter().fold(f.debug_list(), |b, e| b.entry(e)).finish()
     }
 }