Auto merge of #23162 - sfackler:debug-builders, r=alexcrichton

I've made some minor changes from the implementation attached to the RFC to try to minimize codegen. The methods now take `&Debug` trait objects rather than being parameterized and there are inlined stub methods that call to non-inlined methods to do the work.

r? @alexcrichton 

cc @huonw for the `derive(Debug)` changes.

Author: bors

src/libcore/fmt/builders.rs

@@ -0,0 +1,301 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use prelude::*;
+use fmt::{self, Write, FlagV1};
+
+struct PadAdapter<'a, 'b: 'a> {
+    fmt: &'a mut fmt::Formatter<'b>,
+    on_newline: bool,
+}
+
+impl<'a, 'b: 'a> PadAdapter<'a, 'b> {
+    fn new(fmt: &'a mut fmt::Formatter<'b>) -> PadAdapter<'a, 'b> {
+        PadAdapter {
+            fmt: fmt,
+            on_newline: false,
+        }
+    }
+}
+
+impl<'a, 'b: 'a> fmt::Write for PadAdapter<'a, 'b> {
+    fn write_str(&mut self, mut s: &str) -> fmt::Result {
+        while !s.is_empty() {
+            if self.on_newline {
+                try!(self.fmt.write_str("    "));
+            }
+
+            let split = match s.find('\n') {
+                Some(pos) => {
+                    self.on_newline = true;
+                    pos + 1
+                }
+                None => {
+                    self.on_newline = false;
+                    s.len()
+                }
+            };
+            try!(self.fmt.write_str(&s[..split]));
+            s = &s[split..];
+        }
+
+        Ok(())
+    }
+}
+
+/// A struct to help with `fmt::Debug` implementations.
+///
+/// Constructed by the `Formatter::debug_struct` method.
+#[must_use]
+pub struct DebugStruct<'a, 'b: 'a> {
+    fmt: &'a mut fmt::Formatter<'b>,
+    result: fmt::Result,
+    has_fields: bool,
+}
+
+pub fn debug_struct_new<'a, 'b>(fmt: &'a mut fmt::Formatter<'b>, name: &str)
+                                -> DebugStruct<'a, 'b> {
+    let result = fmt.write_str(name);
+    DebugStruct {
+        fmt: fmt,
+        result: result,
+        has_fields: false,
+    }
+}
+
+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> {
+        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, name, value))
+            } else {
+                write!(self.fmt, "{} {}: {:?}", prefix, name, value)
+            }
+        });
+
+        self.has_fields = true;
+        self
+    }
+
+    /// Consumes the `DebugStruct`, finishing output and returning any error
+    /// encountered.
+    #[unstable(feature = "debug_builders", reason = "method was just created")]
+    pub fn finish(mut self) -> fmt::Result {
+        if self.has_fields {
+            self.result = self.result.and_then(|_| {
+                if self.is_pretty() {
+                    self.fmt.write_str("\n}")
+                } else {
+                    self.fmt.write_str(" }")
+                }
+            });
+        }
+        self.result
+    }
+
+    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_tuple` method.
+#[must_use]
+pub struct DebugTuple<'a, 'b: 'a> {
+    fmt: &'a mut fmt::Formatter<'b>,
+    result: fmt::Result,
+    has_fields: bool,
+}
+
+pub fn debug_tuple_new<'a, 'b>(fmt: &'a mut fmt::Formatter<'b>, name: &str) -> DebugTuple<'a, 'b> {
+    let result = fmt.write_str(name);
+    DebugTuple {
+        fmt: fmt,
+        result: result,
+        has_fields: false,
+    }
+}
+
+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> {
+        self.result = self.result.and_then(|_| {
+            let (prefix, space) = if self.has_fields {
+                (",", " ")
+            } else {
+                ("(", "")
+            };
+
+            if self.is_pretty() {
+                let mut writer = PadAdapter::new(self.fmt);
+                fmt::write(&mut writer, format_args!("{}\n{:#?}", prefix, value))
+            } else {
+                write!(self.fmt, "{}{}{:?}", prefix, space, value)
+            }
+        });
+
+        self.has_fields = true;
+        self
+    }
+
+    /// Consumes the `DebugTuple`, finishing output and returning any error
+    /// encountered.
+    #[unstable(feature = "debug_builders", reason = "method was just created")]
+    pub fn finish(mut self) -> fmt::Result {
+        if self.has_fields {
+            self.result = self.result.and_then(|_| {
+                if self.is_pretty() {
+                    self.fmt.write_str("\n)")
+                } else {
+                    self.fmt.write_str(")")
+                }
+            });
+        }
+        self.result
+    }
+
+    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,
+}
+
+pub fn debug_set_new<'a, 'b>(fmt: &'a mut fmt::Formatter<'b>, name: &str) -> DebugSet<'a, 'b> {
+    let result = write!(fmt, "{} {{", name);
+    DebugSet {
+        fmt: fmt,
+        result: result,
+        has_fields: false,
+    }
+}
+
+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
+    }
+
+    /// 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)
+        })
+    }
+
+    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_map` method.
+#[must_use]
+pub struct DebugMap<'a, 'b: 'a> {
+    fmt: &'a mut fmt::Formatter<'b>,
+    result: fmt::Result,
+    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);
+    DebugMap {
+        fmt: fmt,
+        result: result,
+        has_fields: false,
+    }
+}
+
+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> {
+        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, key, value))
+            } else {
+                write!(self.fmt, "{} {:?}: {:?}", prefix, key, value)
+            }
+        });
+
+        self.has_fields = true;
+
+        self
+    }
+
+    /// Consumes the `DebugMap`, 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)
+        })
+    }
+
+    fn is_pretty(&self) -> bool {
+        self.fmt.flags() & (1 << (FlagV1::Alternate as usize)) != 0
+    }
+}