Move all gitignore matching to separate crate.

This PR introduces a new sub-crate, `ignore`, which primarily provides a
fast recursive directory iterator that respects ignore files like
gitignore and other configurable filtering rules based on globs or even
file types.

This results in a substantial source of complexity moved out of ripgrep's
core and into a reusable component that others can now (hopefully)
benefit from.

While much of the ignore code carried over from ripgrep's core, a
substantial portion of it was rewritten with the following goals in
mind:

1. Reuse matchers built from gitignore files across directory iteration.
2. Design the matcher data structure to be amenable for parallelizing
   directory iteration. (Indeed, writing the parallel iterator is the
   next step.)

Fixes #9, #44, #45

1 files changed, 202 insertions, 0 deletions

diff --git a/ignore/src/overrides.rs b/ignore/src/overrides.rs
new file mode 100644
index 00000000..c53a50f7
--- /dev/null
+++ b/ignore/src/overrides.rs
@@ -0,0 +1,202 @@
+/*!
+The overrides module provides a way to specify a set of override globs.
+This provides functionality similar to `--include` or `--exclude` in command
+line tools.
+*/
+
+use std::path::Path;
+
+use gitignore::{self, Gitignore, GitignoreBuilder};
+use {Error, Match};
+
+/// Glob represents a single glob in an override matcher.
+///
+/// This is used to report information about the highest precedent glob
+/// that matched.
+///
+/// Note that not all matches necessarily correspond to a specific glob. For
+/// example, if there are one or more whitelist globs and a file path doesn't
+/// match any glob in the set, then the file path is considered to be ignored.
+///
+/// The lifetime `'a` refers to the lifetime of the matcher that produced
+/// this glob.
+#[derive(Clone, Debug)]
+pub struct Glob<'a>(GlobInner<'a>);
+
+#[derive(Clone, Debug)]
+enum GlobInner<'a> {
+    /// No glob matched, but the file path should still be ignored.
+    UnmatchedIgnore,
+    /// A glob matched.
+    Matched(&'a gitignore::Glob),
+}
+
+impl<'a> Glob<'a> {
+    fn unmatched() -> Glob<'a> {
+        Glob(GlobInner::UnmatchedIgnore)
+    }
+}
+
+/// Manages a set of overrides provided explicitly by the end user.
+#[derive(Clone, Debug)]
+pub struct Override(Gitignore);
+
+impl Override {
+    /// Returns an empty matcher that never matches any file path.
+    pub fn empty() -> Override {
+        Override(Gitignore::empty())
+    }
+
+    /// Returns the directory of this override set.
+    ///
+    /// All matches are done relative to this path.
+    pub fn path(&self) -> &Path {
+        self.0.path()
+    }
+
+    /// Returns true if and only if this matcher is empty.
+    ///
+    /// When a matcher is empty, it will never match any file path.
+    pub fn is_empty(&self) -> bool {
+        self.0.is_empty()
+    }
+
+    /// Returns the total number of ignore globs.
+    pub fn num_ignores(&self) -> u64 {
+        self.0.num_whitelists()
+    }
+
+    /// Returns the total number of whitelisted globs.
+    pub fn num_whitelists(&self) -> u64 {
+        self.0.num_ignores()
+    }
+
+    /// Returns whether the given file path matched a pattern in this override
+    /// matcher.
+    ///
+    /// `is_dir` should be true if the path refers to a directory and false
+    /// otherwise.
+    ///
+    /// If there are no overrides, then this always returns `Match::None`.
+    ///
+    /// If there is at least one whitelist override, then this never returns
+    /// `Match::None`, since non-matches are interpreted as ignored.
+    ///
+    /// The given path is matched to the globs relative to the path given
+    /// when building the override matcher. Specifically, before matching
+    /// `path`, its prefix (as determined by a common suffix of the directory
+    /// given) is stripped. If there is no common suffix/prefix overlap, then
+    /// `path` is assumed to reside in the same directory as the root path for
+    /// this set of overrides.
+    pub fn matched<'a, P: AsRef<Path>>(
+        &'a self,
+        path: P,
+        is_dir: bool,
+    ) -> Match<Glob<'a>> {
+        if self.is_empty() {
+            return Match::None;
+        }
+        let mat = self.0.matched(path, is_dir).invert();
+        if mat.is_none() && self.num_whitelists() > 0 {
+            return Match::Ignore(Glob::unmatched());
+        }
+        mat.map(move |giglob| Glob(GlobInner::Matched(giglob)))
+    }
+}
+
+/// Builds a matcher for a set of glob overrides.
+pub struct OverrideBuilder {
+    builder: GitignoreBuilder,
+}
+
+impl OverrideBuilder {
+    /// Create a new override builder.
+    ///
+    /// Matching is done relative to the directory path provided.
+    pub fn new<P: AsRef<Path>>(path: P) -> OverrideBuilder {
+        OverrideBuilder {
+            builder: GitignoreBuilder::new(path),
+        }
+    }
+
+    /// Builds a new override matcher from the globs added so far.
+    ///
+    /// Once a matcher is built, no new globs can be added to it.
+    pub fn build(&self) -> Result<Override, Error> {
+        Ok(Override(try!(self.builder.build())))
+    }
+
+    /// Add a glob to the set of overrides.
+    ///
+    /// Globs provided here have precisely the same semantics as a single
+    /// line in a `gitignore` file, where the meaning of `!` is inverted:
+    /// namely, `!` at the beginning of a glob will ignore a file. Without `!`,
+    /// all matches of the glob provided are treated as whitelist matches.
+    pub fn add(&mut self, glob: &str) -> Result<&mut OverrideBuilder, Error> {
+        try!(self.builder.add_line(None, glob));
+        Ok(self)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{Override, OverrideBuilder};
+
+    const ROOT: &'static str = "/home/andrew/foo";
+
+    fn ov(globs: &[&str]) -> Override {
+        let mut builder = OverrideBuilder::new(ROOT);
+        for glob in globs {
+            builder.add(glob).unwrap();
+        }
+        builder.build().unwrap()
+    }
+
+    #[test]
+    fn empty() {
+        let ov = ov(&[]);
+        assert!(ov.matched("a.foo", false).is_none());
+        assert!(ov.matched("a", false).is_none());
+        assert!(ov.matched("", false).is_none());
+    }
+
+    #[test]
+    fn simple() {
+        let ov = ov(&["*.foo", "!*.bar"]);
+        assert!(ov.matched("a.foo", false).is_whitelist());
+        assert!(ov.matched("a.foo", true).is_whitelist());
+        assert!(ov.matched("a.rs", false).is_ignore());
+        assert!(ov.matched("a.rs", true).is_ignore());
+        assert!(ov.matched("a.bar", false).is_ignore());
+        assert!(ov.matched("a.bar", true).is_ignore());
+    }
+
+    #[test]
+    fn only_ignores() {
+        let ov = ov(&["!*.bar"]);
+        assert!(ov.matched("a.rs", false).is_none());
+        assert!(ov.matched("a.rs", true).is_none());
+        assert!(ov.matched("a.bar", false).is_ignore());
+        assert!(ov.matched("a.bar", true).is_ignore());
+    }
+
+    #[test]
+    fn precedence() {
+        let ov = ov(&["*.foo", "!*.bar.foo"]);
+        assert!(ov.matched("a.foo", false).is_whitelist());
+        assert!(ov.matched("a.baz", false).is_ignore());
+        assert!(ov.matched("a.bar.foo", false).is_ignore());
+    }
+
+    #[test]
+    fn gitignore() {
+        let ov = ov(&["/foo", "bar/*.rs", "baz/**"]);
+        assert!(ov.matched("bar/wat/lib.rs", false).is_ignore());
+        assert!(ov.matched("wat/bar/lib.rs", false).is_whitelist());
+        assert!(ov.matched("foo", false).is_whitelist());
+        assert!(ov.matched("wat/foo", false).is_ignore());
+        assert!(ov.matched("baz", false).is_ignore());
+        assert!(ov.matched("baz/a", false).is_whitelist());
+        assert!(ov.matched("baz/a/b", false).is_whitelist());
+    }
+}