Auto merge of #25548 - sfackler:debug-builders-by-ref, r=alexcrichton

Based on feedback from https://internals.rust-lang.org/t/final-comment-period-for-debug-builders-stabilization/2007/2

2 files changed, 50 insertions, 25 deletions

diff --git a/src/libcore/fmt/builders.rs b/src/libcore/fmt/builders.rs
index f61a7f2d30c..c1786dc4c28 100644
--- a/src/libcore/fmt/builders.rs
+++ b/src/libcore/fmt/builders.rs
@@ -73,7 +73,7 @@ pub fn debug_struct_new<'a, 'b>(fmt: &'a mut fmt::Formatter<'b>, name: &str)
 impl<'a, 'b: 'a> DebugStruct<'a, 'b> {
     /// Adds a new field to the generated struct output.
     #[unstable(feature = "debug_builders", reason = "method was just created")]
-    pub fn field(mut self, name: &str, value: &fmt::Debug) -> DebugStruct<'a, 'b> {
+    pub fn field(&mut self, name: &str, value: &fmt::Debug) -> &mut DebugStruct<'a, 'b> {
         self.result = self.result.and_then(|_| {
             let prefix = if self.has_fields {
                 ","
@@ -93,10 +93,9 @@ impl<'a, 'b: 'a> DebugStruct<'a, 'b> {
         self
     }
 
-    /// Consumes the `DebugStruct`, finishing output and returning any error
-    /// encountered.
+    /// Finishes output and returns any error encountered.
     #[unstable(feature = "debug_builders", reason = "method was just created")]
-    pub fn finish(mut self) -> fmt::Result {
+    pub fn finish(&mut self) -> fmt::Result {
         if self.has_fields {
             self.result = self.result.and_then(|_| {
                 if self.is_pretty() {
@@ -136,7 +135,7 @@ pub fn debug_tuple_new<'a, 'b>(fmt: &'a mut fmt::Formatter<'b>, name: &str) -> D
 impl<'a, 'b: 'a> DebugTuple<'a, 'b> {
     /// Adds a new field to the generated tuple struct output.
     #[unstable(feature = "debug_builders", reason = "method was just created")]
-    pub fn field(mut self, value: &fmt::Debug) -> DebugTuple<'a, 'b> {
+    pub fn field(&mut self, value: &fmt::Debug) -> &mut DebugTuple<'a, 'b> {
         self.result = self.result.and_then(|_| {
             let (prefix, space) = if self.has_fields {
                 (",", " ")
@@ -156,10 +155,9 @@ impl<'a, 'b: 'a> DebugTuple<'a, 'b> {
         self
     }
 
-    /// Consumes the `DebugTuple`, finishing output and returning any error
-    /// encountered.
+    /// Finishes output and returns any error encountered.
     #[unstable(feature = "debug_builders", reason = "method was just created")]
-    pub fn finish(mut self) -> fmt::Result {
+    pub fn finish(&mut self) -> fmt::Result {
         if self.has_fields {
             self.result = self.result.and_then(|_| {
                 if self.is_pretty() {
@@ -231,15 +229,24 @@ pub fn debug_set_new<'a, 'b>(fmt: &'a mut fmt::Formatter<'b>) -> DebugSet<'a, 'b
 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> {
+    pub fn entry(&mut self, entry: &fmt::Debug) -> &mut DebugSet<'a, 'b> {
         self.inner.entry(entry);
         self
     }
 
-    /// Consumes the `DebugSet`, finishing output and returning any error
-    /// encountered.
+    /// Adds the contents of an iterator of entries to the set output.
     #[unstable(feature = "debug_builders", reason = "method was just created")]
-    pub fn finish(mut self) -> fmt::Result {
+    pub fn entries<D, I>(&mut self, entries: I) -> &mut DebugSet<'a, 'b>
+            where D: fmt::Debug, I: IntoIterator<Item=D> {
+        for entry in entries {
+            self.entry(&entry);
+        }
+        self
+    }
+
+    /// Finishes output and returns 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("}"))
     }
@@ -265,17 +272,26 @@ pub fn debug_list_new<'a, 'b>(fmt: &'a mut fmt::Formatter<'b>) -> DebugList<'a,
 }
 
 impl<'a, 'b: 'a> DebugList<'a, 'b> {
-    /// Adds a new entry to the set output.
+    /// Adds a new entry to the list output.
     #[unstable(feature = "debug_builders", reason = "method was just created")]
-    pub fn entry(mut self, entry: &fmt::Debug) -> DebugList<'a, 'b> {
+    pub fn entry(&mut self, entry: &fmt::Debug) -> &mut DebugList<'a, 'b> {
         self.inner.entry(entry);
         self
     }
 
-    /// Consumes the `DebugSet`, finishing output and returning any error
-    /// encountered.
+    /// Adds the contents of an iterator of entries to the list output.
+    #[unstable(feature = "debug_builders", reason = "method was just created")]
+    pub fn entries<D, I>(&mut self, entries: I) -> &mut DebugList<'a, 'b>
+            where D: fmt::Debug, I: IntoIterator<Item=D> {
+        for entry in entries {
+            self.entry(&entry);
+        }
+        self
+    }
+
+    /// Finishes output and returns any error encountered.
     #[unstable(feature = "debug_builders", reason = "method was just created")]
-    pub fn finish(mut self) -> fmt::Result {
+    pub fn finish(&mut self) -> fmt::Result {
         self.inner.finish();
         self.inner.result.and_then(|_| self.inner.fmt.write_str("]"))
     }
@@ -303,7 +319,7 @@ pub fn debug_map_new<'a, 'b>(fmt: &'a mut fmt::Formatter<'b>) -> DebugMap<'a, 'b
 impl<'a, 'b: 'a> DebugMap<'a, 'b> {
     /// Adds a new entry to the map output.
     #[unstable(feature = "debug_builders", reason = "method was just created")]
-    pub fn entry(mut self, key: &fmt::Debug, value: &fmt::Debug) -> DebugMap<'a, 'b> {
+    pub fn entry(&mut self, key: &fmt::Debug, value: &fmt::Debug) -> &mut DebugMap<'a, 'b> {
         self.result = self.result.and_then(|_| {
             if self.is_pretty() {
                 let mut writer = PadAdapter::new(self.fmt);
@@ -319,10 +335,19 @@ impl<'a, 'b: 'a> DebugMap<'a, 'b> {
         self
     }
 
-    /// Consumes the `DebugMap`, finishing output and returning any error
-    /// encountered.
+    /// Adds the contents of an iterator of entries to the map output.
+    #[unstable(feature = "debug_builders", reason = "method was just created")]
+    pub fn entries<K, V, I>(&mut self, entries: I) -> &mut DebugMap<'a, 'b>
+            where K: fmt::Debug, V: fmt::Debug, I: IntoIterator<Item=(K, V)> {
+        for (k, v) in entries {
+            self.entry(&k, &v);
+        }
+        self
+    }
+
+    /// Finishes output and returns any error encountered.
     #[unstable(feature = "debug_builders", reason = "method was just created")]
-    pub fn finish(self) -> fmt::Result {
+    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))
     }
diff --git a/src/libcore/fmt/mod.rs b/src/libcore/fmt/mod.rs
index a87f6619fe8..22575f340d7 100644
--- a/src/libcore/fmt/mod.rs
+++ b/src/libcore/fmt/mod.rs
@@ -787,7 +787,7 @@ impl<'a> Formatter<'a> {
     ///
     /// 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()
+    ///         fmt.debug_list().entries(self.0.iter()).finish()
     ///     }
     /// }
     ///
@@ -813,7 +813,7 @@ impl<'a> Formatter<'a> {
     ///
     /// impl fmt::Debug for Foo {
     ///     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
-    ///         self.0.iter().fold(fmt.debug_set(), |b, e| b.entry(e)).finish()
+    ///         fmt.debug_set().entries(self.0.iter()).finish()
     ///     }
     /// }
     ///
@@ -839,7 +839,7 @@ impl<'a> Formatter<'a> {
     ///
     /// impl fmt::Debug for Foo {
     ///     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
-    ///         self.0.iter().fold(fmt.debug_map(), |b, &(ref k, ref v)| b.entry(k, v)).finish()
+    ///         fmt.debug_map().entries(self.0.iter().map(|&(ref k, ref v)| (k, v))).finish()
     ///     }
     /// }
     ///
@@ -1120,7 +1120,7 @@ tuple! { T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, }
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Debug> Debug for [T] {
     fn fmt(&self, f: &mut Formatter) -> Result {
-        self.iter().fold(f.debug_list(), |b, e| b.entry(e)).finish()
+        f.debug_list().entries(self.iter()).finish()
     }
 }