fix: update the --frozen logic to error when there is no lockfile (#373)

closes #371 

Error when there is no lockfile and the `--frozen` option is used.

docs/cli.mdx

@@ -60,7 +60,7 @@ Which gets generated on `pixi add` or when you manually change the `pixi.toml` f
 
 - `--manifest-path`: the path to `pixi.toml`, by default it searches for one in the parent directories.
 - `--frozen`: install the environment as defined in the lockfile. Without checking the status of the lockfile.
-- `--locked`: only install if lockfile is up-to-date. Conflicts with `--frozen`.
+- `--locked`: only install if the `pixi.lock` is up-to-date with the `pixi.toml`[^1]. Conflicts with `--frozen`.
 
 ```shell
 pixi install
@@ -81,7 +81,7 @@ You cannot run `pixi run source setup.bash` as `source` is not available in the
 
 - `--manifest-path`: the path to `pixi.toml`, by default it searches for one in the parent directories.
 - `--frozen`: install the environment as defined in the lockfile. Without checking the status of the lockfile.
-- `--locked`: only install if lockfile is up-to-date. Conflicts with `--frozen`.
+- `--locked`: only install if the `pixi.lock` is up-to-date with the `pixi.toml`[^1]. Conflicts with `--frozen`.
 
 ```shell
 pixi run python
@@ -167,7 +167,7 @@ To exit the pixi shell, simply run `exit`.
 
 - `--manifest-path`: the path to `pixi.toml`, by default it searches for one in the parent directories.
 - `--frozen`: install the environment as defined in the lockfile. Without checking the status of the lockfile.
-- `--locked`: only install if lockfile is up-to-date. Conflicts with `--frozen`.
+- `--locked`: only install if the `pixi.lock` is up-to-date with the `pixi.toml`[^1]. Conflicts with `--frozen`.
 
 ```shell
 pixi shell
@@ -328,3 +328,10 @@ pixi project channel add file:///home/user/local_channel
 pixi project channel add https://repo.prefix.dev/conda-forge
 pixi project channel add --no-install robostack
 ```
+
+[^1]: An __up-to-date__ lockfile means that the dependencies in the lockfile are allowed by the dependencies in the manifest file.
+    For example
+    - a `pixi.toml` with `python = ">= 3.11"` is up-to-date with a `name: python, version: 3.11.0` in the `pixi.lock`.
+    - a `pixi.toml` with `python = ">= 3.12"` is **not** up-to-date with a `name: python, version: 3.11.0` in the `pixi.lock`.
+
+    Being up-to-date does **not** mean that the lockfile holds the latest version available on the channel for the given dependency.

src/environment.rs

@@ -74,15 +74,18 @@ pub async fn get_up_to_date_prefix(
     if frozen && locked {
         miette::bail!("Frozen and Locked can't be true at the same time, as using frozen will ignore the locked variable.");
     }
-    let lock_file = load_lock_file(project).await?;
-    let lock_file = if frozen || lock_file_up_to_date(project, &lock_file)? {
-        lock_file
-    } else {
+    if frozen && !project.lock_file_path().is_file() {
+        miette::bail!("No lockfile available, can't do a frozen installation.");
+    }
+
+    let mut lock_file = load_lock_file(project).await?;
+
+    if !frozen && !lock_file_up_to_date(project, &lock_file)? {
         if locked {
             miette::bail!("Lockfile not up-to-date with the project");
         }
-        update_lock_file(project, lock_file, None).await?
-    };
+        lock_file = update_lock_file(project, lock_file, None).await?
+    }
 
     // Update the environment
     update_prefix(