skeleton continues

src/color.rs

@@ -34,10 +34,16 @@ impl Display for _LazyLockDisplay {
     }
 }
 
+pub(crate) const ANSI_GREEN: _LazyLockDisplay = _LazyLockDisplay(LazyLock::new(|| {
+    SHOULD_COLOR.then_some("\x1b[32m").unwrap_or_default()
+}));
+
+pub(crate) const ANSI_MAGENTA: _LazyLockDisplay = _LazyLockDisplay(LazyLock::new(|| {
+    SHOULD_COLOR.then_some("\x1b[35m").unwrap_or_default()
+}));
+
 pub(crate) const ANSI_CYAN: _LazyLockDisplay = _LazyLockDisplay(LazyLock::new(|| {
-    SHOULD_COLOR
-        .then_some("\x1b[36m")
-        .unwrap_or_default()
+    SHOULD_COLOR.then_some("\x1b[36m").unwrap_or_default()
 }));
 
 pub(crate) const ANSI_RESET: _LazyLockDisplay = _LazyLockDisplay(LazyLock::new(|| {

src/lib.rs

@@ -1,3 +1,5 @@
+use std::{io::BufWriter, sync::Arc};
+
 pub(crate) mod prelude {
     #![allow(unused_imports)]
 
@@ -27,22 +29,20 @@ pub(crate) mod prelude {
 
 use prelude::*;
 
-use std::{
-    io::{BufRead, BufReader},
-    sync::Arc,
-};
-
 pub mod args;
 pub use args::Parser;
 mod color;
 pub use color::{CLI_ENABLE_COLOR, SHOULD_COLOR};
 pub mod line;
+mod nixcmd;
 pub use line::Line;
 pub mod source;
 pub use source::SourceLine;
 
 use serde::{Deserialize, Serialize};
 
+use crate::source::SourceFile;
+
 #[derive(Debug, Clone, PartialEq, Hash, Serialize, Deserialize)]
 pub struct DefinitionWithLocation {
     pub file: Box<Path>,
@@ -59,57 +59,29 @@ pub fn get_where(option_name: &str, configuration_nix: &Path) -> Result<Box<Path
     .into_iter()
     .map(ToOwned::to_owned)
     .collect();
-    let result = Command::new("nix-instantiate")
-        .arg("--eval")
-        .arg("--json")
-        .arg("--strict")
-        .arg("--expr")
-        .arg(expr)
-        .arg("-A")
-        .arg(format!("options.{}.definitionsWithLocations", option_name))
+
+    let attrpath = format!("options.{}.definitionsWithLocations", option_name);
+
+    let output = nixcmd::NixEvalExpr { expr, attrpath }
+        .into_command()
         .output_checked_utf8()?;
-    let stdout = result.stdout();
+    let stdout = output.stdout();
 
     let definitions: Box<[DefinitionWithLocation]> = serde_json::from_str(&stdout)?;
-    let last_location = definitions.last().unwrap();
-    let file = &*last_location.file;
-    dbg!(&file);
+    let last_location = definitions.into_iter().last().unwrap();
 
-    Ok(Box::from(file))
+    Ok(Box::from(last_location.file))
 }
 
 pub fn get_highest_prio(
     option_name: &str,
-    file_with_definition: &Path,
+    mut source: SourceFile,
 ) -> Result<SourceLine, BoxDynError> {
-    let mut file = File::options()
-        .read(true)
-        .write(true)
-        .create(false)
-        .custom_flags(libc::O_CLOEXEC)
-        .open(file_with_definition)?;
-
-    // TODO: seek and read backwards.
-
-    let mut lines = BufReader::new(&mut file)
-        .lines()
-        .enumerate()
-        .map(|(index, line_res)| {
-            line_res.map(|line| SourceLine {
-                line: Line::from_index(index as u64),
-                path: Arc::from(file_with_definition),
-                text: Arc::from(line),
-            })
-        })
-        .collect::<Result<Vec<SourceLine>, IoError>>()?;
-    lines.reverse();
-    let lines_reversed = lines;
-
     // Get the current highest priority.
 
     let expr: OsString = [
         OsStr::new("import <nixpkgs/nixos> { configuration = "),
-        file_with_definition.as_os_str(),
+        source.path().as_os_str(),
         OsStr::new("; }"),
     ]
     .into_iter()
@@ -117,41 +89,40 @@ pub fn get_highest_prio(
     .collect();
 
     // Get the highest priority, and the file its defined in.
-    let result = Command::new("nix-instantiate")
-        .arg("--eval")
-        .arg("--json")
-        .arg("--strict")
-        .arg("--expr")
-        .arg(expr)
-        .arg("-A")
-        .arg(format!("options.{}.highestPrio", option_name))
+    let attrpath = format!("options.{}.highestPrio", option_name);
+    let output = nixcmd::NixEvalExpr { expr, attrpath }
+        .into_command()
         .output_checked_utf8()?;
-    let stdout = result.stdout();
+    let stdout = output.stdout();
     let highest_prio = stdout.trim();
 
     let needle = format!("lib.mkOverride ({})", highest_prio);
-    eprintln!("looking for {needle:?}");
 
-    let line_with_current_highest = lines_reversed
+    let path = source.path();
+    let lines = source.lines()?;
+    let line = lines
         .iter()
-        .position(|line| {
-            eprintln!("looking for {needle} in {line}");
-
-            line.text.contains(&needle)
-        })
+        // We're more likely to find it at the end, so let's start there.
+        .rev()
+        .find(|&line| line.text.contains(&needle))
         .unwrap_or_else(|| {
             panic!(
                 "couldn't find override number {highest_prio} in {}",
-                file_with_definition.display()
+                path.display(),
             )
         });
 
-    let line = lines_reversed
-        .into_iter()
-        .nth(line_with_current_highest)
-        .unwrap();
-
-    eprintln!("found, on line index {}", line);
-
-    Ok(line)
+    Ok(line.clone())
+}
+
+pub fn write_next_prio(
+    mut source: SourceFile,
+    last_line_def: SourceLine,
+    new_prio: u64,
+) -> Result<(), BoxDynError> {
+    let lines = source.lines()?;
+
+    for line in lines {}
+
+    Ok(())
 }

src/main.rs

@@ -1,17 +1,20 @@
-use std::error::Error as StdError;
-use std::io::IsTerminal;
+use std::{error::Error as StdError, sync::Arc};
+use std::io::{self, IsTerminal};
 use std::path::Path;
 use std::process::ExitCode;
 
 
+use append_override::source::SourceFile;
 use clap::{ColorChoice, Parser as _};
+use fs_err::File;
+use fs_err::os::unix::fs::OpenOptionsExt;
 
 fn main_wrapped() -> Result<(), Box<dyn StdError + Send + Sync + 'static>> {
     let args = append_override::Parser::parse();
 
     let success = append_override::CLI_ENABLE_COLOR.set(match args.color {
         ColorChoice::Always => true,
-        ColorChoice::Auto => std::io::stdin().is_terminal(),
+        ColorChoice::Auto => io::stdin().is_terminal(),
         ColorChoice::Never => false,
     });
     if cfg!(debug_assertions) {
@@ -23,8 +26,18 @@ fn main_wrapped() -> Result<(), Box<dyn StdError + Send + Sync + 'static>> {
 
     // Get what file that thing is defined in.
     let def_path = append_override::get_where(&args.name, filepath)?;
+    let def_path = Arc::from(def_path);
+    let mut opts = File::options();
+    opts
+        .read(true)
+        .write(true)
+        .create(false)
+        .custom_flags(libc::O_CLOEXEC);
+    let source_file = SourceFile::open_from(Arc::clone(&def_path), opts)?;
 
-    append_override::get_highest_prio(&args.name, &def_path)?;
+    let last_def_line = append_override::get_highest_prio(&args.name, source_file)?;
+
+    eprintln!("{last_def_line}");
 
     Ok(())
 }

src/nixcmd.rs

@@ -0,0 +1,27 @@
+#[allow(unused_imports)]
+use crate::prelude::*;
+
+#[derive(Debug, Clone, PartialEq, Hash)]
+pub(crate) struct NixEvalExpr<E, A> {
+    pub(crate) expr: E,
+    pub(crate) attrpath: A,
+}
+
+impl<E, A> NixEvalExpr<E, A>
+where
+    E: AsRef<OsStr>,
+    A: AsRef<OsStr>,
+{
+    pub(crate) fn into_command(self) -> Command {
+        let mut cmd = Command::new("nix-instantiate");
+        cmd.arg("--eval")
+            .arg("--json")
+            .arg("--strict")
+            .arg("--expr")
+            .arg(self.expr)
+            .arg("-A")
+            .arg(self.attrpath);
+
+        cmd
+    }
+}

src/source.rs

@@ -1,12 +1,16 @@
 use std::{
-    hash::{Hash, Hasher},
-    sync::{Arc, LazyLock},
+    hash::Hash,
+    io::{BufRead, BufReader},
+    ops::{Deref, DerefMut},
+    sync::{Arc, Mutex, MutexGuard, OnceLock, PoisonError},
 };
 
 use crate::Line;
+use crate::color::{ANSI_CYAN, ANSI_GREEN, ANSI_MAGENTA, ANSI_RESET};
 #[allow(unused_imports)]
 use crate::prelude::*;
-use crate::color::{ANSI_CYAN, ANSI_RESET};
+
+use fs_err::OpenOptions;
 
 #[derive(Debug, Clone, PartialEq, Hash)]
 pub struct SourceLine {
@@ -17,7 +21,13 @@ pub struct SourceLine {
 
 impl Display for SourceLine {
     fn fmt(&self, f: &mut Formatter) -> FmtResult {
-        write!(f, "line {:03}: `{ANSI_CYAN}{}{ANSI_RESET}`", self.line.linenr(), self.text.trim())
+        write!(
+            f,
+            "{ANSI_MAGENTA}{}{ANSI_RESET}:{ANSI_GREEN}{}{ANSI_RESET}: `{ANSI_CYAN}{}{ANSI_RESET}`",
+            self.path.display(),
+            self.line.linenr(),
+            self.text.trim(),
+        )
     }
 }
 
@@ -29,31 +39,64 @@ pub struct SourcePath {
 #[derive(Debug, Clone)]
 pub struct SourceFile {
     path: Arc<Path>,
-    file: Arc<File>,
+    file: Arc<Mutex<File>>,
+    lines: Arc<OnceLock<Vec<SourceLine>>>,
+}
+
+impl SourceFile {
+    pub fn open_from(path: Arc<Path>, options: OpenOptions) -> Result<Self, IoError> {
+        let file = Arc::new(Mutex::new(options.open(&*path)?));
+
+        Ok(Self {
+            path,
+            file,
+            lines: Arc::new(OnceLock::new()),
+        })
+    }
+
+    pub fn buf_reader(&mut self) -> Result<BufReader<&mut File>, IoError> {
+        let file_mut = Arc::get_mut(&mut self.file)
+            .unwrap_or_else(|| panic!("'File' for {} has existing handle", self.path.display()))
+            .get_mut()
+            .unwrap_or_else(|e| {
+                panic!("'File' for {} was mutex-poisoned: {e}", self.path.display())
+            });
+
+        let reader = BufReader::new(file_mut);
+
+        Ok(reader)
+    }
+
+    pub fn lines(&self) -> Result<&[SourceLine], IoError> {
+        if let Some(lines) = self.lines.get() {
+            return Ok(lines);
+        }
+        let lines = BufReader::new(&*self.file.lock().unwrap())
+            .lines()
+            .enumerate()
+            .map(|(index, line_res)| {
+                line_res.map(|line| SourceLine {
+                    line: Line::from_index(index as u64),
+                    path: Arc::clone(&self.path),
+                    text: Arc::from(line),
+                })
+            })
+            .collect::<Result<Vec<SourceLine>, IoError>>()?;
+        // Mutex should have dropped by now.
+        debug_assert!(self.file.try_lock().is_ok());
+
+        self.lines.set(lines).unwrap();
+
+        Ok(self.lines.get().unwrap().as_slice())
+    }
+
+    pub fn path(&self) -> Arc<Path> {
+        Arc::clone(&self.path)
+    }
 }
 
 impl PartialEq for SourceFile {
     fn eq(&self, other: &Self) -> bool {
-        let paths_match = *self.path == *other.path;
-        if paths_match && self.file.as_raw_fd() != other.file.as_raw_fd() {
-            todo!("handle the case where source file paths match but FD numbers don't");
-        }
-        paths_match
+        *self.path == *other.path
     }
 }
-
-impl Hash for SourceFile {
-    fn hash<H: Hasher>(&self, state: &mut H) {
-        self.path.hash(state);
-        self.file.as_raw_fd().hash(state);
-    }
-}
-
-#[derive(Debug, Clone, PartialEq, Hash)]
-enum SourceInner {
-    Path(SourcePath),
-    File(SourceFile),
-}
-
-#[derive(Debug, Clone, PartialEq, Hash)]
-pub struct Source(SourceInner);