Use fmt::Write instead of io::Write in write.rs.

It is common to represent a function as a String, and previously that
required re-validating the UTF-8 in a Vec<u8>. The fmt::Write trait
writes UTF-8 directly into a String, so no extra checking is required.

This also means we can implement Display for Function which gives it a
to_string() method. This makes the function_to_string() method
redundant, so delete it.

The functions in the write module are no longer generally useful, so
make the module private. The Display trait on Function is all we need.

cranelift/src/libcretonne/ir/function.rs

@@ -6,7 +6,8 @@
 use ir::{FunctionName, Signature, StackSlot, StackSlotData, JumpTable, JumpTableData,
          DataFlowGraph, Layout};
 use entity_map::{EntityMap, PrimaryEntityData};
-use std::fmt::{self, Debug, Formatter};
+use std::fmt::{self, Display, Debug, Formatter};
+use write::write_function;
 
 /// A function.
 ///
@@ -60,9 +61,14 @@ impl Function {
     }
 }
 
-impl Debug for Function {
+impl Display for Function {
     fn fmt(&self, fmt: &mut Formatter) -> fmt::Result {
-        use write::function_to_string;
-        fmt.write_str(&function_to_string(self))
+        write_function(fmt, self)
+    }
+}
+
+impl Debug for Function {
+    fn fmt(&self, fmt: &mut Formatter) -> fmt::Result {
+        write_function(fmt, self)
     }
 }

cranelift/src/libcretonne/lib.rs

@@ -9,13 +9,13 @@ pub const VERSION: &'static str = env!("CARGO_PKG_VERSION");
 
 pub mod ir;
 pub mod isa;
-pub mod write;
 pub mod cfg;
 pub mod dominator_tree;
 pub mod entity_map;
 pub mod settings;
 pub mod verifier;
 
+mod write;
 mod constant_hash;
 mod predicates;
 

cranelift/src/libcretonne/write.rs

@@ -5,9 +5,8 @@
 //! `cretonne-reader` crate.
 
 use ir::{Function, Ebb, Inst, Value, Type};
-use std::io::{self, Write};
-
-pub type Result = io::Result<()>;
+use std::fmt::{Result, Error, Write};
+use std::result;
 
 /// Write `func` to `w` as equivalent text.
 pub fn write_function(w: &mut Write, func: &Function) -> Result {
@@ -24,15 +23,6 @@ pub fn write_function(w: &mut Write, func: &Function) -> Result {
     writeln!(w, "}}")
 }
 
-/// Convert `func` to a string.
-pub fn function_to_string(func: &Function) -> String {
-    let mut buffer: Vec<u8> = Vec::new();
-    // Any errors here would be out-of-memory, which should not happen with normal functions.
-    write_function(&mut buffer, func).unwrap();
-    // A UTF-8 conversion error is a real bug.
-    String::from_utf8(buffer).unwrap()
-}
-
 // ====--------------------------------------------------------------------------------------====//
 //
 // Function spec.
@@ -65,7 +55,7 @@ fn write_spec(w: &mut Write, func: &Function) -> Result {
     }
 }
 
-fn write_preamble(w: &mut Write, func: &Function) -> io::Result<bool> {
+fn write_preamble(w: &mut Write, func: &Function) -> result::Result<bool, Error> {
     let mut any = false;
 
     for ss in func.stack_slots.keys() {
@@ -218,7 +208,6 @@ pub fn write_instruction(w: &mut Write, func: &Function, inst: Inst) -> Result {
 
 #[cfg(test)]
 mod tests {
-    use super::*;
     use super::{needs_quotes, escaped};
     use ir::{Function, StackSlotData};
     use ir::types;
@@ -244,26 +233,26 @@ mod tests {
     #[test]
     fn basic() {
         let mut f = Function::new();
-        assert_eq!(function_to_string(&f), "function \"\"() {\n}\n");
+        assert_eq!(f.to_string(), "function \"\"() {\n}\n");
 
         f.name.push_str("foo");
-        assert_eq!(function_to_string(&f), "function foo() {\n}\n");
+        assert_eq!(f.to_string(), "function foo() {\n}\n");
 
         f.stack_slots.push(StackSlotData::new(4));
-        assert_eq!(function_to_string(&f),
+        assert_eq!(f.to_string(),
                    "function foo() {\n    ss0 = stack_slot 4\n}\n");
 
         let ebb = f.dfg.make_ebb();
         f.layout.append_ebb(ebb);
-        assert_eq!(function_to_string(&f),
+        assert_eq!(f.to_string(),
                    "function foo() {\n    ss0 = stack_slot 4\n\nebb0:\n}\n");
 
         f.dfg.append_ebb_arg(ebb, types::I8);
-        assert_eq!(function_to_string(&f),
+        assert_eq!(f.to_string(),
                    "function foo() {\n    ss0 = stack_slot 4\n\nebb0(vx0: i8):\n}\n");
 
         f.dfg.append_ebb_arg(ebb, types::F32.by(4).unwrap());
-        assert_eq!(function_to_string(&f),
+        assert_eq!(f.to_string(),
                    "function foo() {\n    ss0 = stack_slot 4\n\nebb0(vx0: i8, vx1: f32x4):\n}\n");
     }
 }

cranelift/src/tools/cat.rs

@@ -3,11 +3,9 @@
 //! Read a sequence of Cretonne IL files and print them again to stdout. This has the effect of
 //! normalizing formatting and removing comments.
 
-use std::io;
 use CommandResult;
 use utils::read_to_string;
 use cton_reader::parse_functions;
-use cretonne::write::write_function;
 
 pub fn run(files: Vec<String>) -> CommandResult {
     for (i, f) in files.into_iter().enumerate() {
@@ -27,9 +25,7 @@ fn cat_one(filename: String) -> CommandResult {
         if idx != 0 {
             println!("");
         }
-        let stdout = io::stdout();
-        let mut handle = stdout.lock();
-        try!(write_function(&mut handle, &func).map_err(|e| format!("{}: {}", filename, e)));
+        print!("{}", func);
     }
 
     Ok(())