6 files changed, 326 insertions, 208 deletions

diff --git a/bin/src/config.rs b/bin/src/config.rs
index 6d7bc49..202ff6c 100644
--- a/bin/src/config.rs
+++ b/bin/src/config.rs
@@ -15,118 +15,74 @@ use crate::err::ConfigErr;
 #[derive(Clap, Debug)]
 #[clap(version = "0.1.0", author = "Akshay <[email protected]>")]
 pub struct Opts {
-    /// File or directory to run statix on
-    #[clap(default_value = ".")]
-    pub target: String,
+    #[clap(subcommand)]
+    pub cmd: SubCommand,
+}
+
+#[derive(Clap, Debug)]
+pub enum SubCommand {
+    /// Lints and suggestions for the nix programming language
+    Check(Check),
+    /// Find and fix issues raised by statix-check
+    Fix(Fix),
+    /// Fix exactly one issue at provided position
+    Single(Single),
+}
+
+#[derive(Clap, Debug)]
+pub struct Check {
+    /// File or directory to run check on
+    #[clap(default_value = ".", parse(from_os_str))]
+    target: PathBuf,
 
     /// Globs of file patterns to skip
     #[clap(short, long)]
-    pub ignore: Vec<String>,
+    ignore: Vec<String>,
 
     /// Output format.
     /// Supported values: errfmt, json (on feature flag only)
-    #[clap(short = 'o', long)]
-    format: Option<OutFormat>,
-
-    /// Find and fix issues raised by statix
-    #[clap(short = 'f', long)]
-    pub fix: bool,
-
-    /// Do not fix files in place, display a diff instead
-    #[clap(short = 'd', long = "dry-run")]
-    diff_only: bool,
-}
-
-
-#[derive(Debug, Copy, Clone)]
-pub enum OutFormat {
-    #[cfg(feature = "json")]
-    Json,
-    Errfmt,
-    StdErr,
+    #[clap(short = 'o', long, default_value = "OutFormat::StdErr")]
+    pub format: OutFormat,
 }
 
-impl Default for OutFormat {
-    fn default() -> Self {
-        OutFormat::StdErr
+impl Check {
+    pub fn vfs(&self) -> Result<ReadOnlyVfs, ConfigErr> {
+        let files = walk_with_ignores(&self.ignore, &self.target)?;
+        vfs(files)
     }
 }
 
-impl FromStr for OutFormat {
-    type Err = &'static str;
+#[derive(Clap, Debug)]
+pub struct Fix {
+    /// File or directory to run fix on
+    #[clap(default_value = ".", parse(from_os_str))]
+    target: PathBuf,
 
-    fn from_str(value: &str) -> Result<Self, Self::Err> {
-        match value.to_ascii_lowercase().as_str() {
-            #[cfg(feature = "json")] "json" => Ok(Self::Json),
-            "errfmt" => Ok(Self::Errfmt),
-            "stderr" => Ok(Self::StdErr),
-            "json" => Err("statix was not compiled with the `json` feature flag"),
-            _ => Err("unknown output format, try: json, errfmt"),
-        }
-    }
-}
+    /// Globs of file patterns to skip
+    #[clap(short, long)]
+    ignore: Vec<String>,
 
-#[derive(Debug)]
-pub struct LintConfig {
-    pub files: Vec<PathBuf>,
-    pub format: OutFormat,
+    /// Do not fix files in place, display a diff instead
+    #[clap(short, long = "dry-run")]
+    pub diff_only: bool,
 }
 
-impl LintConfig {
-    pub fn from_opts(opts: Opts) -> Result<Self, ConfigErr> {
-        let ignores = build_ignore_set(&opts.ignore).map_err(|err| {
-            ConfigErr::InvalidGlob(err.glob().map(|i| i.to_owned()), err.kind().clone())
-        })?;
-
-        let files = walk_nix_files(&opts.target)?
-            .filter(|path| !ignores.is_match(path))
-            .collect();
-
-        Ok(Self {
-            files,
-            format: opts.format.unwrap_or_default(),
-        })
-    }
-
+impl Fix {
     pub fn vfs(&self) -> Result<ReadOnlyVfs, ConfigErr> {
-        let mut vfs = ReadOnlyVfs::default();
-        for file in self.files.iter() {
-            let _id = vfs.alloc_file_id(&file);
-            let data = fs::read_to_string(&file).map_err(ConfigErr::InvalidPath)?;
-            vfs.set_file_contents(&file, data.as_bytes());
-        }
-        Ok(vfs)
+        let files = walk_with_ignores(&self.ignore, &self.target)?;
+        vfs(files)
     }
 }
 
-pub struct FixConfig {
-    pub files: Vec<PathBuf>,
-    pub diff_only: bool,
-}
-
-impl FixConfig {
-    pub fn from_opts(opts: Opts) -> Result<Self, ConfigErr> {
-        let ignores = build_ignore_set(&opts.ignore).map_err(|err| {
-            ConfigErr::InvalidGlob(err.glob().map(|i| i.to_owned()), err.kind().clone())
-        })?;
-
-        let files = walk_nix_files(&opts.target)?
-            .filter(|path| !ignores.is_match(path))
-            .collect();
-
-        let diff_only = opts.diff_only;
-        Ok(Self { files, diff_only })
-    }
-
-    pub fn vfs(&self) -> Result<ReadOnlyVfs, ConfigErr> {
-        let mut vfs = ReadOnlyVfs::default();
-        for file in self.files.iter() {
-            let _id = vfs.alloc_file_id(&file);
-            let data = fs::read_to_string(&file).map_err(ConfigErr::InvalidPath)?;
-            vfs.set_file_contents(&file, data.as_bytes());
-        }
-        Ok(vfs)
-    }
+#[derive(Clap, Debug)]
+pub struct Single {
+    /// File to run single-fix on
+    #[clap(default_value = ".", parse(from_os_str))]
+    pub target: PathBuf,
+
+    /// Position to attempt a fix at
+    #[clap(short, long, parse(try_from_str = parse_line_col))]
+    pub position: (usize, usize),
 }
 
 mod dirs {
@@ -185,7 +141,23 @@ mod dirs {
     }
 }
 
-fn build_ignore_set(ignores: &Vec<String>) -> Result<GlobSet, GlobError> {
+fn parse_line_col(src: &str) -> Result<(usize, usize), ConfigErr> {
+    let parts = src.split(",");
+    match parts.collect::<Vec<_>>().as_slice() {
+        [line, col] => {
+            let l = line
+                .parse::<usize>()
+                .map_err(|_| ConfigErr::InvalidPosition(src.to_owned()))?;
+            let c = col
+                .parse::<usize>()
+                .map_err(|_| ConfigErr::InvalidPosition(src.to_owned()))?;
+            Ok((l, c))
+        }
+        _ => Err(ConfigErr::InvalidPosition(src.to_owned())),
+    }
+}
+
+fn build_ignore_set(ignores: &[String]) -> Result<GlobSet, GlobError> {
     let mut set = GlobSetBuilder::new();
     for pattern in ignores {
         let glob = GlobBuilder::new(&pattern).build()?;
@@ -198,3 +170,56 @@ fn walk_nix_files<P: AsRef<Path>>(target: P) -> Result<impl Iterator<Item = Path
     let walker = dirs::Walker::new(target)?;
     Ok(walker.filter(|path: &PathBuf| matches!(path.extension(), Some(e) if e == "nix")))
 }
+
+fn walk_with_ignores<P: AsRef<Path>>(
+    ignores: &[String],
+    target: P,
+) -> Result<Vec<PathBuf>, ConfigErr> {
+    let ignores = build_ignore_set(ignores).map_err(|err| {
+        ConfigErr::InvalidGlob(err.glob().map(|i| i.to_owned()), err.kind().clone())
+    })?;
+
+    Ok(walk_nix_files(&target)?
+        .filter(|path| !ignores.is_match(path))
+        .collect())
+}
+
+fn vfs(files: Vec<PathBuf>) -> Result<ReadOnlyVfs, ConfigErr> {
+    let mut vfs = ReadOnlyVfs::default();
+    for file in files.iter() {
+        let _id = vfs.alloc_file_id(&file);
+        let data = fs::read_to_string(&file).map_err(ConfigErr::InvalidPath)?;
+        vfs.set_file_contents(&file, data.as_bytes());
+    }
+    Ok(vfs)
+
+}
+
+#[derive(Debug, Copy, Clone)]
+pub enum OutFormat {
+    #[cfg(feature = "json")]
+    Json,
+    Errfmt,
+    StdErr,
+}
+
+impl Default for OutFormat {
+    fn default() -> Self {
+        OutFormat::StdErr
+    }
+}
+
+impl FromStr for OutFormat {
+    type Err = &'static str;
+
+    fn from_str(value: &str) -> Result<Self, Self::Err> {
+        match value.to_ascii_lowercase().as_str() {
+            #[cfg(feature = "json")]
+            "json" => Ok(Self::Json),
+            "errfmt" => Ok(Self::Errfmt),
+            "stderr" => Ok(Self::StdErr),
+            "json" => Err("statix was not compiled with the `json` feature flag"),
+            _ => Err("unknown output format, try: json, errfmt"),
+        }
+    }
+}
diff --git a/bin/src/err.rs b/bin/src/err.rs
index 727e0cc..5f71b57 100644
--- a/bin/src/err.rs
+++ b/bin/src/err.rs
@@ -8,9 +8,10 @@ use thiserror::Error;
 pub enum ConfigErr {
     #[error("error parsing glob `{0:?}`: {1}")]
     InvalidGlob(Option<String>, ErrorKind),
-
     #[error("path error: {0}")]
     InvalidPath(#[from] io::Error),
+    #[error("unable to parse `{0}` as line and column")]
+    InvalidPosition(String)
 }
 
 #[derive(Error, Debug)]
@@ -28,11 +29,25 @@ pub enum FixErr {
 }
 
 #[derive(Error, Debug)]
+pub enum SingleFixErr {
+    #[error("path error: {0}")]
+    InvalidPath(#[from] io::Error),
+    #[error("position out of bounds: line {0}, col {1}")]
+    OutOfBounds(usize, usize),
+    #[error("{0} is too large")]
+    Conversion(usize),
+    #[error("nothing to fix")]
+    NoOp,
+}
+
+#[derive(Error, Debug)]
 pub enum StatixErr {
     #[error("linter error: {0}")]
     Lint(#[from] LintErr),
     #[error("fixer error: {0}")]
     Fix(#[from] FixErr),
+    #[error("single fix error: {0}")]
+    Single(#[from] SingleFixErr),
     #[error("config error: {0}")]
     Config(#[from] ConfigErr),
 }
diff --git a/bin/src/fix.rs b/bin/src/fix.rs
index d9087fe..a7ddc4f 100644
--- a/bin/src/fix.rs
+++ b/bin/src/fix.rs
@@ -1,55 +1,14 @@
 use std::borrow::Cow;
 
-use lib::{Report, LINTS};
-use rnix::{parser::ParseError as RnixParseErr, TextRange, WalkEvent};
+use rnix::TextRange;
 
-type Source<'a> = Cow<'a, str>;
-
-fn collect_fixes(source: &str) -> Result<Vec<Report>, RnixParseErr> {
-    let parsed = rnix::parse(source).as_result()?;
-
-    Ok(parsed
-        .node()
-        .preorder_with_tokens()
-        .filter_map(|event| match event {
-            WalkEvent::Enter(child) => LINTS.get(&child.kind()).map(|rules| {
-                rules
-                    .iter()
-                    .filter_map(|rule| rule.validate(&child))
-                    .filter(|report| report.total_suggestion_range().is_some())
-                    .collect::<Vec<_>>()
-            }),
-            _ => None,
-        })
-        .flatten()
-        .collect())
-}
+mod all;
+pub use all::all;
 
-fn reorder(mut reports: Vec<Report>) -> Vec<Report> {
-    use std::collections::VecDeque;
+mod single;
+pub use single::single;
 
-    reports.sort_by(|a, b| {
-        let a_range = a.range();
-        let b_range = b.range();
-        a_range.end().partial_cmp(&b_range.end()).unwrap()
-    });
-
-    reports
-        .into_iter()
-        .fold(VecDeque::new(), |mut deque: VecDeque<Report>, new_elem| {
-            let front = deque.front();
-            let new_range = new_elem.range();
-            if let Some(front_range) = front.map(|f| f.range()) {
-                if new_range.start() > front_range.end() {
-                    deque.push_front(new_elem);
-                }
-            } else {
-                deque.push_front(new_elem);
-            }
-            deque
-        })
-        .into()
-}
+type Source<'a> = Cow<'a, str>;
 
 #[derive(Debug)]
 pub struct FixResult<'a> {
@@ -68,37 +27,3 @@ impl<'a> FixResult<'a> {
         Self { src, fixed: Vec::new() }
     }
 }
-
-impl<'a> Iterator for FixResult<'a> {
-    type Item = FixResult<'a>;
-    fn next(&mut self) -> Option<Self::Item> {
-        let all_reports = collect_fixes(&self.src).ok()?;
-        if all_reports.is_empty() {
-            return None;
-        }
-
-        let reordered = reorder(all_reports);
-        let fixed = reordered
-            .iter()
-            .map(|r| Fixed {
-                at: r.range(),
-                code: r.code,
-            })
-            .collect::<Vec<_>>();
-        for report in reordered {
-            report.apply(self.src.to_mut());
-        }
-
-        Some(FixResult {
-            src: self.src.clone(),
-            fixed
-        })
-    }
-}
-
-pub fn fix(src: &str) -> Option<FixResult> {
-    let src = Cow::from(src);
-    let _ = rnix::parse(&src).as_result().ok()?;
-    let initial = FixResult::empty(src);
-    initial.into_iter().last()
-}
diff --git a/bin/src/fix/all.rs b/bin/src/fix/all.rs
new file mode 100644
index 0000000..8c0770d
--- /dev/null
+++ b/bin/src/fix/all.rs
@@ -0,0 +1,86 @@
+use std::borrow::Cow;
+
+use lib::{Report, LINTS};
+use rnix::{parser::ParseError as RnixParseErr, WalkEvent};
+
+use crate::fix::{Fixed, FixResult};
+
+fn collect_fixes(source: &str) -> Result<Vec<Report>, RnixParseErr> {
+    let parsed = rnix::parse(source).as_result()?;
+
+    Ok(parsed
+        .node()
+        .preorder_with_tokens()
+        .filter_map(|event| match event {
+            WalkEvent::Enter(child) => LINTS.get(&child.kind()).map(|rules| {
+                rules
+                    .iter()
+                    .filter_map(|rule| rule.validate(&child))
+                    .filter(|report| report.total_suggestion_range().is_some())
+                    .collect::<Vec<_>>()
+            }),
+            _ => None,
+        })
+        .flatten()
+        .collect())
+}
+
+fn reorder(mut reports: Vec<Report>) -> Vec<Report> {
+    use std::collections::VecDeque;
+
+    reports.sort_by(|a, b| {
+        let a_range = a.range();
+        let b_range = b.range();
+        a_range.end().partial_cmp(&b_range.end()).unwrap()
+    });
+
+    reports
+        .into_iter()
+        .fold(VecDeque::new(), |mut deque: VecDeque<Report>, new_elem| {
+            let front = deque.front();
+            let new_range = new_elem.range();
+            if let Some(front_range) = front.map(|f| f.range()) {
+                if new_range.start() > front_range.end() {
+                    deque.push_front(new_elem);
+                }
+            } else {
+                deque.push_front(new_elem);
+            }
+            deque
+        })
+        .into()
+}
+
+impl<'a> Iterator for FixResult<'a> {
+    type Item = FixResult<'a>;
+    fn next(&mut self) -> Option<Self::Item> {
+        let all_reports = collect_fixes(&self.src).ok()?;
+        if all_reports.is_empty() {
+            return None;
+        }
+
+        let reordered = reorder(all_reports);
+        let fixed = reordered
+            .iter()
+            .map(|r| Fixed {
+                at: r.range(),
+                code: r.code,
+            })
+            .collect::<Vec<_>>();
+        for report in reordered {
+            report.apply(self.src.to_mut());
+        }
+
+        Some(FixResult {
+            src: self.src.clone(),
+            fixed
+        })
+    }
+}
+
+pub fn all(src: &str) -> Option<FixResult> {
+    let src = Cow::from(src);
+    let _ = rnix::parse(&src).as_result().ok()?;
+    let initial = FixResult::empty(src);
+    initial.into_iter().last()
+}
diff --git a/bin/src/fix/single.rs b/bin/src/fix/single.rs
new file mode 100644
index 0000000..d430693
--- /dev/null
+++ b/bin/src/fix/single.rs
@@ -0,0 +1,59 @@
+use std::{borrow::Cow, convert::TryFrom};
+
+use lib::{Report, LINTS};
+use rnix::{TextRange, TextSize};
+
+use crate::err::SingleFixErr;
+use crate::fix::Source;
+
+pub struct SingleFixResult<'δ> {
+    pub src: Source<'δ>,
+}
+
+fn pos_to_byte(line: usize, col: usize, src: &str) -> Result<TextSize, SingleFixErr> {
+    let mut byte: TextSize = TextSize::of("");
+    for (_, l) in src.lines().enumerate().take_while(|(i, _)| i <= &line) {
+        byte += TextSize::of(l);
+    }
+    byte += TextSize::try_from(col).map_err(|_| SingleFixErr::Conversion(col))?;
+
+    if usize::from(byte) >= src.len() {
+        Err(SingleFixErr::OutOfBounds(line, col))
+    } else {
+        Ok(byte)
+    }
+}
+
+fn find(offset: TextSize, src: &str) -> Result<Report, SingleFixErr> {
+    // we don't really need the source to form a completely parsed tree
+    let parsed = rnix::parse(src);
+
+    let elem_at = parsed
+        .node()
+        .child_or_token_at_range(TextRange::empty(offset))
+        .ok_or(SingleFixErr::NoOp)?;
+
+    LINTS
+        .get(&elem_at.kind())
+        .map(|rules| {
+            rules
+                .iter()
+                .filter_map(|rule| rule.validate(&elem_at))
+                .filter(|report| report.total_suggestion_range().is_some())
+                .next()
+        })
+        .flatten()
+        .ok_or(SingleFixErr::NoOp)
+}
+
+pub fn single(line: usize, col: usize, src: &str) -> Result<SingleFixResult, SingleFixErr> {
+    let mut src = Cow::from(src);
+    let offset = pos_to_byte(line, col, &*src)?;
+    let report = find(offset, &*src)?;
+
+    report.apply(src.to_mut());
+
+    Ok(SingleFixResult {
+        src
+    })
+}
diff --git a/bin/src/main.rs b/bin/src/main.rs
index d0f69a0..9c57d91 100644
--- a/bin/src/main.rs
+++ b/bin/src/main.rs
@@ -6,50 +6,58 @@ mod traits;
 
 use std::io;
 
-use crate::{err::{StatixErr, FixErr}, traits::WriteDiagnostic};
+use crate::{err::{StatixErr, FixErr, SingleFixErr}, traits::WriteDiagnostic};
 
 use clap::Clap;
-use config::{FixConfig, LintConfig, Opts};
+use config::{Opts, SubCommand};
 use similar::TextDiff;
 
 fn _main() -> Result<(), StatixErr> {
     let opts = Opts::parse();
-    if opts.fix {
-        let fix_config = FixConfig::from_opts(opts)?;
-        let vfs = fix_config.vfs()?;
-        for entry in vfs.iter() {
-            if let Some(fix_result) = fix::fix(entry.contents) {
-                if fix_config.diff_only {
-                    let text_diff = TextDiff::from_lines(entry.contents, &fix_result.src);
-                    let old_file = format!("{}", entry.file_path.display());
-                    let new_file = format!("{} [fixed]", entry.file_path.display());
-                    println!(
-                        "{}",
-                        text_diff
+    match opts.cmd {
+        SubCommand::Check(check_config) => {
+            let vfs = check_config.vfs()?;
+            let (lints, errors): (Vec<_>, Vec<_>) = vfs.iter().map(lint::lint).partition(Result::is_ok);
+            let lint_results = lints.into_iter().map(Result::unwrap);
+            let errors = errors.into_iter().map(Result::unwrap_err);
+
+            let mut stdout = io::stdout();
+            lint_results.for_each(|r| {
+                stdout.write(&r, &vfs, check_config.format).unwrap();
+            });
+            errors.for_each(|e| {
+                eprintln!("{}", e);
+            });
+        },
+        SubCommand::Fix(fix_config) => {
+            let vfs = fix_config.vfs()?;
+            for entry in vfs.iter() {
+                if let Some(fix_result) = fix::all(entry.contents) {
+                    if fix_config.diff_only {
+                        let text_diff = TextDiff::from_lines(entry.contents, &fix_result.src);
+                        let old_file = format!("{}", entry.file_path.display());
+                        let new_file = format!("{} [fixed]", entry.file_path.display());
+                        println!(
+                            "{}",
+                            text_diff
                             .unified_diff()
                             .context_radius(4)
                             .header(&old_file, &new_file)
-                    );
-                } else {
-                    let path = entry.file_path;
-                    std::fs::write(path, &*fix_result.src).map_err(FixErr::InvalidPath)?;
+                            );
+                    } else {
+                        let path = entry.file_path;
+                        std::fs::write(path, &*fix_result.src).map_err(FixErr::InvalidPath)?;
+                    }
                 }
             }
+        },
+        SubCommand::Single(single_config) => {
+            let path = single_config.target;
+            let src = std::fs::read_to_string(&path).map_err(SingleFixErr::InvalidPath)?;
+            let (line, col) = single_config.position;
+            let single_result = fix::single(line, col, &src)?;
+            std::fs::write(&path, &*single_result.src).map_err(SingleFixErr::InvalidPath)?;
         }
-    } else {
-        let lint_config = LintConfig::from_opts(opts)?;
-        let vfs = lint_config.vfs()?;
-        let (lints, errors): (Vec<_>, Vec<_>) = vfs.iter().map(lint::lint).partition(Result::is_ok);
-        let lint_results = lints.into_iter().map(Result::unwrap);
-        let errors = errors.into_iter().map(Result::unwrap_err);
-
-        let mut stdout = io::stdout();
-        lint_results.for_each(|r| {
-            stdout.write(&r, &vfs, lint_config.format).unwrap();
-        });
-        errors.for_each(|e| {
-            eprintln!("{}", e);
-        });
     }
     Ok(())
 }