Pre-update commands (fix #25)

README.md

@@ -55,6 +55,14 @@ git_repos = [
     "~/dev/topgrade",
 ]
 
+[pre_commands]
+"Emacs Snapshot" = "rm -rf ~/.emacs.d/elpa.bak && cp -rl ~/.emacs.d/elpa ~/.emacs.d/elpa.bak"
+
 [commands]
 "Python Environment" = "~/dev/.env/bin/pip install -i https://pypi.python.org/simple -U --upgrade-strategy eager jupyter"
 ```
+* `git_repos` - A list of custom Git repositories to pull
+* `pre_commands` - Commands to execute before starting any action. If any command fails, Topgrade
+  will not proceed
+* `commands` - Custom upgrade steps. If any command fails it will be reported in the summary as all
+  upgrade steps are reported, but it will not cause Topgrade to stop.

src/config.rs

@@ -5,9 +5,12 @@ use std::collections::BTreeMap;
 use std::fs;
 use toml;
 
+type Commands = BTreeMap<String, String>;
+
 #[derive(Deserialize, Default)]
 pub struct Config {
-    commands: Option<BTreeMap<String, String>>,
+    pre_commands: Option<Commands>,
+    commands: Option<Commands>,
     git_repos: Option<Vec<String>>,
 }
 
@@ -30,7 +33,11 @@ impl Config {
         Ok(result)
     }
 
-    pub fn commands(&self) -> &Option<BTreeMap<String, String>> {
+    pub fn pre_commands(&self) -> &Option<Commands> {
+        &self.pre_commands
+    }
+
+    pub fn commands(&self) -> &Option<Commands> {
         &self.commands
     }
 

src/main.rs

@@ -71,6 +71,13 @@ fn run() -> Result<(), Error> {
         None
     };
 
+    if let Some(commands) = config.pre_commands() {
+        for (name, command) in commands {
+            terminal.print_separator(name);
+            run_custom_command(&command)?;
+        }
+    }
+
     if cfg!(target_os = "linux") {
         terminal.print_separator("System update");
         match linux::Distribution::detect() {