cli: writing the custom migration dir to the config file

diesel_cli/src/main.rs

@@ -96,8 +96,8 @@ where
 
 #[tracing::instrument]
 fn run_setup_command(matches: &ArgMatches) -> Result<(), crate::errors::Error> {
-    create_config_file(matches)?;
     let migrations_dir = create_migrations_dir(matches)?;
+    create_config_file(matches, &migrations_dir)?;
 
     database::setup_database(matches, &migrations_dir)?;
     Ok(())
@@ -136,12 +136,20 @@ fn create_migrations_dir(matches: &ArgMatches) -> Result<PathBuf, crate::errors:
     Ok(dir)
 }
 
-fn create_config_file(matches: &ArgMatches) -> Result<(), crate::errors::Error> {
+fn create_config_file(
+    matches: &ArgMatches,
+    migrations_dir: &Path,
+) -> Result<(), crate::errors::Error> {
     use std::io::Write;
     let path = Config::file_path(matches);
     if !path.exists() {
+        let source_content = include_str!("default_files/diesel.toml").to_string();
+        let modified_content = source_content.replace(
+            "dir = \"migrations\"",
+            &format!("dir = \"{}\"", migrations_dir.display()),
+        );
         let mut file = fs::File::create(path)?;
-        file.write_all(include_bytes!("default_files/diesel.toml"))?;
+        file.write_all(modified_content.as_bytes())?;
     }
 
     Ok(())

diesel_cli/tests/setup.rs

@@ -170,6 +170,22 @@ fn setup_works_with_migration_dir_by_arg() {
     assert!(p.has_file("foo"));
 }
 
+#[test]
+fn setup_writes_migration_dir_by_arg_to_config_file() {
+    let p = project("setup_writes_migration_dir_by_arg_to_config_file").build();
+
+    // make sure the project builder doesn't create it for us
+    assert!(!p.has_file("migrations"));
+    assert!(!p.has_file("foo"));
+
+    let result = p.command("setup").arg("--migration-dir=foo").run();
+
+    assert!(result.is_success(), "Result was unsuccessful {:?}", result);
+    assert!(!p.has_file("migrations"));
+    assert!(p.has_file("foo"));
+    assert!(p.file_contents("diesel.toml").contains("dir = \"foo\""));
+}
+
 #[test]
 fn setup_works_with_migration_dir_by_env() {
     let p = project("setup_works_with_migration_dir_by_env").build();