Add support for diesel migration generate migration_name to CLI

This command will create a timestamped directory in the migrations
folder, along with the empty files `up.sql` and `down.sql`. Right now
I'm spitting out absolute paths, it would be nice to print them as
relative instead (unsure if this should be relative to the cwd or to the
parent of the migrations directory).

Author: sgrif

diesel/src/migrations/mod.rs

@@ -216,7 +216,7 @@ fn revert_migration(conn: &Connection, migration: Box<Migration>)
 /// of the current directory, until it reaches the directory containing
 /// `Cargo.toml`. Returns `MigrationError::MigrationDirectoryNotFound`
 /// if no directory is found.
-fn find_migrations_directory() -> Result<PathBuf, MigrationError> {
+pub fn find_migrations_directory() -> Result<PathBuf, MigrationError> {
     search_for_migrations_directory(&try!(env::current_dir()))
 }
 

diesel_cli/Cargo.toml

@@ -9,3 +9,4 @@ name = "diesel"
 [dependencies]
 diesel = "^0.3.0"
 clap = "^1.5.5"
+chrono = "^0.2.17"

diesel_cli/src/main.rs

@@ -1,10 +1,12 @@
+extern crate chrono;
 #[macro_use]
 extern crate clap;
 extern crate diesel;
 
+use chrono::*;
 use clap::{App, AppSettings, Arg, ArgMatches, SubCommand};
 use diesel::migrations;
-use std::env;
+use std::{env, fs};
 
 fn main() {
     let database_arg = || Arg::with_name("DATABASE_URL")
@@ -70,7 +72,20 @@ fn run_migration_command(matches: &ArgMatches) {
             }).unwrap();
         }
         ("generate", Some(args)) => {
-            panic!("Migration generator is not implemented this pass")
+            let migration_name = args.value_of("MIGRATION_NAME").unwrap();
+            let timestamp = Local::now().format("%Y%m%d%H%M%S");
+            let versioned_name = format!("{}_{}", &timestamp, migration_name);
+            let migration_dir = migrations::find_migrations_directory()
+                .unwrap().join(versioned_name);
+            fs::create_dir(&migration_dir).unwrap();
+
+            // FIXME: It would be nice to print these as relative paths
+            let up_path = migration_dir.join("up.sql");
+            println!("Creating {}", up_path.display());
+            fs::File::create(up_path).unwrap();
+            let down_path = migration_dir.join("down.sql");
+            println!("Creating {}", down_path.display());
+            fs::File::create(down_path).unwrap();
         }
         _ => unreachable!("The cli parser should prevent reaching here"),
     }