Fix nushell with --nom, make shell bits templated (#62)

The nu template uses the executable very differently from others, so it
ends up trying weird things like `which nix-your-shell --nom`, which
fails because `which` doesn't understand `--nom`.

The other shell templates are also broken as shell _scripts_, because
they rely on the `nix-your-shell` -> `nix-your-shell $shell`
substitution.

Fix everything by using a real template engine.

Cargo.toml

@@ -16,6 +16,7 @@ calm_io = "0.1.1"
 camino = "1.1.4"
 clap = { version = "4.3.4", features = ["derive", "wrap_help", "env"] }
 color-eyre = "0.6.2"
+minijinja = { version = "1.0.12", features = ["json"] }
 shell-words = "1.1.0"
 tracing = { version = "0.1.39", features = ["attributes"] }
 tracing-subscriber = { version = "0.3.17", features = ["env-filter", "registry"] }

data/env.fish → data/env.fish.j2

@@ -2,9 +2,9 @@
 # nix-your-shell | source
 
 function nix-shell --description "Start an interactive shell based on a Nix expression"
-    nix-your-shell nix-shell -- $argv
+    {{ executable }} {{ extra_args | join(" ") }} fish nix-shell -- $argv
 end
 
 function nix --description "Reproducible and declarative configuration management"
-    nix-your-shell nix -- $argv
+    {{ executable }} {{ extra_args | join(" ") }} fish nix -- $argv
 end

data/env.nu → data/env.nu.j2

@@ -2,9 +2,14 @@
 # nix-your-shell nu | save nix-your-shell.nu
 
 def _nix_your_shell (command: string, args: list<string>) {
-  if not (which nix-your-shell | is-empty) {
+  if not (which {{ executable }} | is-empty) {
+    {%- if extra_args %}
+    {#- If you squint hard enough, JSON lists are just Nu lists #}
+    let args = {{ extra_args | tojson }} ++ ["--"] ++ $args
+    {%- else %}
     let args = ["--"] ++ $args
-    run-external nix-your-shell $command ...$args
+    {%- endif %}
+    run-external {{ executable }} $command ...$args
   } else {
     run-external $command ...$args
   }

data/env.sh → data/env.sh.j2

@@ -2,9 +2,9 @@
 # nix-your-shell | source /dev/stdin
 
 function nix-shell () {
-    nix-your-shell nix-shell -- "$@"
+    {{ executable }} {{ extra_args | join(" ") }} {{ shell }} nix-shell -- "$@"
 }
 
 function nix () {
-    nix-your-shell nix -- "$@"
+    {{ executable }} {{ extra_args | join(" ") }} {{ shell }} nix -- "$@"
 }

data/env.xsh.j2

@@ -0,0 +1,5 @@
+# If you see this output, you probably forgot to pipe it into `source`:
+# nix-your-shell | source
+
+aliases['nix-shell'] = '{{ executable }} {{ extra_args | join(" ") }} xonsh nix-shell -- @($args)'
+aliases['nix'] = '{{ executable }} {{ extra_args | join(" ") }} xonsh nix -- @($args)'

src/main.rs

@@ -93,21 +93,21 @@ fn main() -> eyre::Result<()> {
 
     match opts.command.unwrap_or_default() {
         Command::Env => {
-            let mut shell_code = match shell.kind {
+            let template = match shell.kind {
                 ShellKind::Zsh | ShellKind::Bash => {
-                    include_str!("../data/env.sh")
+                    include_str!("../data/env.sh.j2")
                 }
 
                 ShellKind::Fish => {
-                    include_str!("../data/env.fish")
+                    include_str!("../data/env.fish.j2")
                 }
 
                 ShellKind::Nushell => {
-                    include_str!("../data/env.nu")
+                    include_str!("../data/env.nu.j2")
                 }
 
                 ShellKind::Xonsh => {
-                    include_str!("../data/env.xsh")
+                    include_str!("../data/env.xsh.j2")
                 }
 
                 ShellKind::Other(shell) => {
@@ -116,31 +116,23 @@ fn main() -> eyre::Result<()> {
                     ))
                     .note("Supported shells are: `zsh`, `fish`, `nushell`, `xonsh`, and `bash`")
                 }
-            }
-            .to_owned();
-
-            // Do some string replacements to reflect the arguments passed to `nix-your-shell` in
-            // the generated code.
-            //
-            // We could make this a bit "cleaner" with an actual templating language, but it's nice
-            // that the snippets in `../data/` are valid code and not templates.
-
-            let mut shell_args = shell_words::quote(shell.path.as_str());
-
-            if opts.nom {
-                shell_args += " --nom";
-            }
-
-            shell_code =
-                shell_code.replace("nix-your-shell", &format!("nix-your-shell {}", shell_args));
+            };
 
             let current_exe =
                 current_exe().wrap_err("Unable to determine absolute path of `nix-your-shell`")?;
-            if opts.absolute || !executable_is_on_path(&current_exe)? {
-                shell_code = shell_code.replace("nix-your-shell", current_exe.as_str());
-            }
 
-            let _ = println!("{shell_code}");
+            let formatted = minijinja::render!(
+                template,
+                executable => if opts.absolute || !executable_is_on_path(&current_exe)? {
+                    current_exe.as_str()
+                } else {
+                    "nix-your-shell"
+                },
+                extra_args => if opts.nom { vec!["--nom"] } else { vec![] },
+                shell => shell.path.as_str(),
+            );
+
+            let _ = println!("{formatted}");
             Ok(())
         }