Implement basic configuration w/Freight.toml file

This commit adds the beginning of a configuration file for Freight.
Eventually we'll make it more robust with parsing when we can add serde
and the like as a dependency but we're a long ways off from that. With
this we can offload configuration from being hardcoded inside of Freight
to a config file that users can use to tailor to their project. It also
lets us get rid of the janky check for ".git" in root_dir and instead
look for a manifest to work with, in this case Freight. Later on we'll
need better toml support so that we can build Cargo projects

Freight.toml

@@ -0,0 +1,2 @@
+name = "freight"
+edition = "2021"

src/config.rs

@@ -0,0 +1,42 @@
+use super::Edition;
+use super::Result;
+use std::error::Error;
+use std::fs;
+use std::path::Path;
+
+pub struct Manifest {
+    pub crate_name: String,
+    pub edition: Edition,
+}
+
+impl Manifest {
+    pub fn parse_from_file(path: impl AsRef<Path>) -> Result<Self> {
+        let path = path.as_ref();
+        let mut crate_name = None;
+        let mut edition = None;
+
+        for line in fs::read_to_string(path)?.lines() {
+            let mut split = line.split('=');
+            let field = split.next().unwrap().trim();
+            let value = split.next().unwrap().trim();
+
+            match field {
+                "name" => crate_name = Some(value.replace('"', "")),
+                "edition" => {
+                    edition = Some(match value.replace('"', "").parse()? {
+                        2015 => Edition::E2015,
+                        2018 => Edition::E2018,
+                        2021 => Edition::E2021,
+                        edition => return Err(format!("Edition {edition} is unsupported").into()),
+                    })
+                }
+                field => return Err(format!("Field {field} is unsupported").into()),
+            }
+        }
+
+        Ok(Self {
+            crate_name: crate_name.ok_or::<Box<dyn Error>>("name is a required field".into())?,
+            edition: edition.ok_or::<Box<dyn Error>>("edition is a required field".into())?,
+        })
+    }
+}

src/lib.rs

@@ -1,3 +1,6 @@
+mod config;
+
+use config::Manifest;
 use std::env;
 use std::error::Error;
 use std::fmt;
@@ -10,10 +13,7 @@ pub type Result<T> = std::result::Result<T, Box<dyn Error>>;
 
 pub fn build() -> Result<()> {
     let root_dir = root_dir()?;
-    // TODO: Get this from a config file
-    let crate_name = root_dir
-        .file_name()
-        .ok_or::<Box<dyn Error>>("Freight run in directory without a name".into())?;
+    let manifest = Manifest::parse_from_file(root_dir.join("Freight.toml"))?;
 
     let lib_rs = root_dir.join("src").join("lib.rs");
     let main_rs = root_dir.join("src").join("main.rs");
@@ -24,9 +24,9 @@ pub fn build() -> Result<()> {
     let lib_compile = || -> Result<()> {
         println!("Compiling lib.rs");
         Rustc::builder()
-            .edition(Edition::E2021)
+            .edition(manifest.edition)
             .crate_type(CrateType::Lib)
-            .crate_name(crate_name.to_str().unwrap())
+            .crate_name(&manifest.crate_name)
             .out_dir(target_debug.clone())
             .lib_dir(target_debug.clone())
             .done()
@@ -38,9 +38,9 @@ pub fn build() -> Result<()> {
     let bin_compile = |externs: Vec<&str>| -> Result<()> {
         println!("Compiling main.rs");
         let mut builder = Rustc::builder()
-            .edition(Edition::E2021)
+            .edition(manifest.edition)
             .crate_type(CrateType::Bin)
-            .crate_name(crate_name.to_str().unwrap())
+            .crate_name(&manifest.crate_name)
             .out_dir(target_debug.clone())
             .lib_dir(target_debug.clone());
 
@@ -56,7 +56,7 @@ pub fn build() -> Result<()> {
     match (lib_rs.exists(), main_rs.exists()) {
         (true, true) => {
             lib_compile()?;
-            bin_compile(vec![crate_name.to_str().unwrap()])?;
+            bin_compile(vec![&manifest.crate_name])?;
         }
         (true, false) => {
             lib_compile()?;
@@ -73,7 +73,7 @@ pub fn build() -> Result<()> {
 fn root_dir() -> Result<PathBuf> {
     let current_dir = env::current_dir()?;
     for ancestor in current_dir.ancestors() {
-        if ancestor.join(".git").exists() {
+        if ancestor.join("Freight.toml").exists() {
             return Ok(ancestor.into());
         }
     }
@@ -183,6 +183,7 @@ impl RustcBuilder {
     }
 }
 
+#[derive(Clone, Copy)]
 pub enum Edition {
     E2015,
     E2018,