Add an expandconfig utility to add default values

This patch adds an `expandconfig` binary which is able to load a
configuration file, and write it back (in either TOML or YAML format)
with the default values expanded.  This is useful in a variety of
scenarios:

 - Check that a configuration file is valid with:

    expandconfig /path/to/config.toml

 - See default field values and structure with:

    expandconfig

 - See all available fields with (YAML displays fields with a default
   `None` value while TOML skips them):

    expandconfig -f yaml

Cargo.toml

@@ -19,6 +19,9 @@ name = "bench-perf-model"
 path = "tools/bench_perf_model/main.rs"
 required-features = ["cuda"]
 
+[[bin]]
+name = "expandconfig"
+
 [[bench]]
 name = "descent"
 harness = false
@@ -76,6 +79,7 @@ rpds = "0.5.0"
 serde = "1.0"
 serde_derive = "1.0"
 serde_json = "1.0.22"
+serde_yaml = "0.8"
 bincode = "1.0"
 std-semaphore = "0.1.0"
 tempfile = "3.0.1"

src/bin/expandconfig.rs

@@ -0,0 +1,113 @@
+extern crate getopts;
+extern crate serde_yaml;
+extern crate toml;
+
+extern crate telamon;
+
+use std::env;
+use std::io::{Read, Write};
+
+use getopts::Options;
+
+enum Format {
+    Toml,
+    Yaml,
+}
+
+/// Expand a configuration.
+///
+/// # Arguments
+///
+///  - input: Path to the input file to use.  If `None`, the default configuration is loaded.  If
+///    "-", the configuration is read from the standard input.
+///
+///  - output: Path to the output file.  If "-", the configuration is printed to the standard
+///    output.
+fn expand_config(input: Option<&str>, output: &str, format: Format) {
+    let input_str = input
+        .map(|input| {
+            let mut input_str = String::new();
+            match input {
+                "-" => {
+                    let stdin = std::io::stdin();
+                    stdin.lock().read_to_string(&mut input_str).unwrap();
+                }
+                _ => {
+                    std::fs::File::open(input)
+                        .unwrap()
+                        .read_to_string(&mut input_str)
+                        .unwrap();
+                }
+            };
+            input_str
+        }).unwrap_or_else(|| "".to_string());
+
+    let config: telamon::explorer::config::Config = toml::from_str(&input_str).unwrap();
+
+    let output_str = match format {
+        Format::Toml => toml::to_string(&config).unwrap(),
+        Format::Yaml => serde_yaml::to_string(&config).unwrap(),
+    };
+
+    match output {
+        "-" => print!("{}", output_str),
+        _ => {
+            write!(std::fs::File::create(output).unwrap(), "{}", output_str);
+        }
+    }
+}
+
+fn print_usage(program: &str, opts: Options) {
+    let brief = format!(
+        "Usage: {} PATH [options]
+
+Loads an explorer configuration file and outputs it with the default values added.  This can also
+be used as a simple validator of an explorer configuration file by discarding the output.
+",
+        program
+    );
+    print!("{}", opts.usage(&brief));
+}
+
+fn main() {
+    let args: Vec<String> = env::args().collect();
+    let program = args[0].clone();
+
+    let mut opts = Options::new();
+    opts.optflag("h", "help", "Prints help information");
+    opts.optopt("o", "output", "Path to the output file", "PATH");
+    opts.optopt("f", "format", "Output format", "[toml|yaml]");
+
+    let matches = match opts.parse(&args[1..]) {
+        Ok(m) => m,
+        Err(f) => panic!(f.to_string()),
+    };
+
+    if matches.opt_present("h") {
+        print_usage(&program, opts);
+        return;
+    }
+
+    let output = matches.opt_str("o").unwrap_or_else(|| "-".to_string());
+    let input = if !matches.free.is_empty() {
+        Some(&matches.free[0][..])
+    } else {
+        None
+    };
+
+    let format = match matches
+        .opt_str("f")
+        .unwrap_or_else(|| "toml".to_string())
+        .to_lowercase()
+        .as_ref()
+    {
+        "yaml" => Format::Yaml,
+        "toml" => Format::Toml,
+        _ => {
+            print_usage(&program, opts);
+            return;
+        }
+    };
+
+    expand_config(input, &output, format);
+}