From 775ba9e6ac31a3b20ecec7ae3c29ca1a7baee3b1 Mon Sep 17 00:00:00 2001
From: oxalica <oxalicc@pm.me>
Date: Mon, 27 Mar 2023 00:07:04 +0800
Subject: [PATCH] Parse flake outputs and add flake package meta

---
 crates/nix-interop/src/flake_output.rs | 101 +++++++++++++++++++++++++
 crates/nix-interop/src/lib.rs          |   1 +
 flake.nix                              |   8 +-
 3 files changed, 109 insertions(+), 1 deletion(-)
 create mode 100644 crates/nix-interop/src/flake_output.rs

diff --git a/crates/nix-interop/src/flake_output.rs b/crates/nix-interop/src/flake_output.rs
new file mode 100644
index 0000000..56c5a85
--- /dev/null
+++ b/crates/nix-interop/src/flake_output.rs
@@ -0,0 +1,101 @@
+use std::collections::HashMap;
+use std::path::Path;
+use std::process::{Command, Stdio};
+
+use anyhow::{ensure, Context, Result};
+use serde::Deserialize;
+
+pub fn eval_flake_output(nix_command: &Path, flake_path: &Path) -> Result<FlakeOutput> {
+    let output = Command::new(nix_command)
+        .args([
+            "flake",
+            "show",
+            "--experimental-features",
+            "nix-command flakes",
+            "--json",
+            "--legacy",
+        ])
+        .arg(flake_path)
+        .stdin(Stdio::null())
+        .stdout(Stdio::piped())
+        .stderr(Stdio::piped())
+        .output()
+        .context("Failed to spawn `nix`")?;
+
+    ensure!(
+        output.status.success(),
+        "`nix flake show` failed with {}. Stderr:\n{}",
+        output.status,
+        String::from_utf8_lossy(&output.stderr),
+    );
+
+    let val = serde_json::from_slice(&output.stdout)?;
+    Ok(val)
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Deserialize)]
+#[serde(untagged)]
+pub enum FlakeOutput {
+    Leaf(Leaf),
+    Attrset(HashMap<String, FlakeOutput>),
+}
+
+impl FlakeOutput {
+    pub fn as_leaf(&self) -> Option<&Leaf> {
+        match self {
+            Self::Leaf(v) => Some(v),
+            _ => None,
+        }
+    }
+
+    pub fn as_attrset(&self) -> Option<&HashMap<String, FlakeOutput>> {
+        match self {
+            Self::Attrset(v) => Some(v),
+            _ => None,
+        }
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct Leaf {
+    #[serde(rename = "type")]
+    pub type_: Type,
+    pub name: Option<String>,
+    pub description: Option<String>,
+}
+
+// https://github.com/NixOS/nix/blob/2.14.1/src/nix/flake.cc#L1105
+#[derive(Debug, Clone, PartialEq, Eq, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub enum Type {
+    NixosModule,
+    Derivation,
+    #[serde(other)]
+    Unknown,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    #[ignore = "requires calling 'nix'"]
+    fn self_() {
+        let dir = std::env::var("CARGO_MANIFEST_DIR").unwrap();
+        let output = eval_flake_output("nix".as_ref(), dir.as_ref()).unwrap();
+        let leaf = (|| {
+            output.as_attrset()?["packages"].as_attrset()?["x86_64-linux"].as_attrset()?["nil"]
+                .as_leaf()
+        })()
+        .unwrap();
+        assert_eq!(leaf.type_, Type::Derivation);
+        assert!(leaf.name.as_ref().unwrap().starts_with("nil-unstable-"));
+        assert!(leaf
+            .description
+            .as_ref()
+            .unwrap()
+            .to_lowercase()
+            .contains("language server"));
+    }
+}
diff --git a/crates/nix-interop/src/lib.rs b/crates/nix-interop/src/lib.rs
index 1c73eef..80cfec2 100644
--- a/crates/nix-interop/src/lib.rs
+++ b/crates/nix-interop/src/lib.rs
@@ -1,6 +1,7 @@
 //! Nix defined file structures and interoperation with Nix.
 pub mod eval;
 pub mod flake_lock;
+pub mod flake_output;
 pub mod nixos_options;
 
 pub const DEFAULT_IMPORT_FILE: &str = "default.nix";
diff --git a/flake.nix b/flake.nix
index 1de021d..cedfc82 100644
--- a/flake.nix
+++ b/flake.nix
@@ -1,4 +1,4 @@
-{
+rec {
   description = "Language Server for Nix Expression Language";
 
   inputs = {
@@ -28,6 +28,12 @@
           nativeBuildInputs = [ nix.out ];
 
           CFG_RELEASE = "git-${rev}";
+
+          meta = {
+            inherit description;
+            homepage = "https://github.com/oxalica/nil";
+            license = with lib.licenses; [ mit asl20 ];
+          };
         };
 
       mkCocNil = { runCommand, nodejs, esbuild }: