Auto merge of #32390 - japaric:untry, r=pnkfelix

convert 99.9% of `try!`s to `?`s

The first commit is an automated conversion using the [untry] tool and the following command:

```
$ find -name '*.rs' -type f | xargs untry
```

at the root of the Rust repo.

[untry]: https://github.com/japaric/untry

cc @rust-lang/lang @alexcrichton @brson

Author: bors

src/compiletest/compiletest.rs

@@ -15,6 +15,7 @@
 #![feature(rustc_private)]
 #![feature(str_char)]
 #![feature(test)]
+#![feature(question_mark)]
 
 #![deny(warnings)]
 
@@ -280,16 +281,16 @@ fn collect_tests_from_dir(config: &Config,
                           -> io::Result<()> {
     // Ignore directories that contain a file
     // `compiletest-ignore-dir`.
-    for file in try!(fs::read_dir(dir)) {
-        let file = try!(file);
+    for file in fs::read_dir(dir)? {
+        let file = file?;
         if file.file_name() == *"compiletest-ignore-dir" {
             return Ok(());
         }
     }
 
-    let dirs = try!(fs::read_dir(dir));
+    let dirs = fs::read_dir(dir)?;
     for file in dirs {
-        let file = try!(file);
+        let file = file?;
         let file_path = file.path();
         debug!("inspecting file {:?}", file_path.display());
         if is_test(config, &file_path) {
@@ -310,11 +311,11 @@ fn collect_tests_from_dir(config: &Config,
             tests.push(make_test(config, &paths))
         } else if file_path.is_dir() {
             let relative_file_path = relative_dir_path.join(file.file_name());
-            try!(collect_tests_from_dir(config,
-                                        base,
-                                        &file_path,
-                                        &relative_file_path,
-                                        tests));
+            collect_tests_from_dir(config,
+                                   base,
+                                   &file_path,
+                                   &relative_file_path,
+                                   tests)?;
         }
     }
     Ok(())

src/libcore/fmt/builders.rs

@@ -29,7 +29,7 @@ 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("    "));
+                self.fmt.write_str("    ")?;
             }
 
             let split = match s.find('\n') {
@@ -42,7 +42,7 @@ impl<'a, 'b: 'a> fmt::Write for PadAdapter<'a, 'b> {
                     s.len()
                 }
             };
-            try!(self.fmt.write_str(&s[..split]));
+            self.fmt.write_str(&s[..split])?;
             s = &s[split..];
         }
 
@@ -169,10 +169,10 @@ impl<'a, 'b: 'a> DebugTuple<'a, 'b> {
         if self.fields > 0 {
             self.result = self.result.and_then(|_| {
                 if self.is_pretty() {
-                    try!(self.fmt.write_str("\n"));
+                    self.fmt.write_str("\n")?;
                 }
                 if self.fields == 1 && self.empty_name {
-                    try!(self.fmt.write_str(","));
+                    self.fmt.write_str(",")?;
                 }
                 self.fmt.write_str(")")
             });