A sketch of the parser API for ignore files (#301)

Use an iterator for flexibility, while parsing what matters and
leaving details to the caller, like generating the actual glob
from the pre-escaped string.

Author: Byron

Cargo.lock

@@ -13,3 +13,5 @@ doctest = false
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+bstr = { version = "0.2.13", default-features = false, features = ["std"]}
+bitflags = "1.3.2"

git-attributes/Cargo.toml

@@ -1 +1,59 @@
 #![forbid(unsafe_code, rust_2018_idioms)]
+
+pub mod ignore {
+    pub mod pattern {
+        use bitflags::bitflags;
+
+        bitflags! {
+            pub struct Mode: u32 {
+                const NO_DIR = 1 << 0;
+                // TODO: find a much better name!
+                const ENDS_WITH = 1 << 1;
+                const MUST_BE_DIR = 1 << 2;
+                const NEGATIVE = 1 << 3;
+            }
+        }
+    }
+}
+
+pub mod parse {
+    pub mod ignore {
+        use crate::ignore;
+        use bstr::{BStr, BString, ByteSlice};
+
+        pub struct Iter<'a> {
+            cursor: &'a BStr,
+        }
+
+        impl<'a> Iter<'a> {
+            pub fn new(buf: &'a [u8]) -> Self {
+                Iter { cursor: buf.as_bstr() }
+            }
+        }
+
+        impl<'a> Iterator for Iter<'a> {
+            type Item = (BString, ignore::pattern::Mode);
+
+            fn next(&mut self) -> Option<Self::Item> {
+                if self.cursor.is_empty() {
+                    return None;
+                }
+                let mut lines = self.cursor.lines();
+                let res = None;
+                while let Some(line) = lines.next() {
+                    if line.starts_with(b"#") {
+                        continue;
+                    }
+                    todo!("handle escapes and trim trailing non-escaped whitespace")
+                }
+                if let Some(next_line) = lines.next() {
+                    self.cursor = next_line.as_bstr();
+                }
+                res
+            }
+        }
+    }
+    pub fn ignore(buf: &[u8]) -> ignore::Iter<'_> {
+        ignore::Iter::new(buf)
+    }
+}

git-attributes/src/lib.rs

@@ -0,0 +1,8 @@
+mod parse {
+    mod ignore {
+        #[test]
+        fn comments_are_ignored() {
+            assert!(git_attributes::parse::ignore(b"# hello world").next().is_none());
+        }
+    }
+}