[esrlabs#1966] Add the BuildConfiguration struct

The BuildConfiguration struct will hold the build configuration loaded
from the configuration file. For the moment it just loads the file
contents into a string and handles failures.

build-cli/.gitignore

@@ -0,0 +1 @@
+target/*

build-cli/src/build_configuration.rs

@@ -0,0 +1,39 @@
+use core::fmt;
+use std::fs;
+
+const DEFAULT_BUILD_CONFIG_FILE:&str = "build.toml";
+
+pub struct ReadError {
+    pub file_name: String,
+    pub message: String
+}
+
+impl fmt::Display for ReadError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}: {}", self.file_name, self.message)
+    }
+}
+
+pub struct BuildConfiguration {
+    pub source_file: String,
+    text: String
+}
+
+impl BuildConfiguration {
+    pub fn from_file(file_name: Option<String>) -> Result<Self, ReadError> {
+        let actual_file_name = file_name.unwrap_or(DEFAULT_BUILD_CONFIG_FILE.to_string());
+        let result = fs::read_to_string(&actual_file_name);
+
+        match result {
+            Err(error) => {
+                Err(ReadError {
+                    file_name: actual_file_name,
+                    message: format!("Unable to read file: {}", error)
+                })
+            },
+            Ok(text) => {
+                Ok(Self { source_file: actual_file_name, text })
+            }
+        }
+    }
+}

build-cli/src/main.rs

@@ -1,3 +1,5 @@
+mod build_configuration;
+
 fn main() {
     println!("Hello, world!");
 }