Add a primitive to parse a \n- or \r\n-terminated line (#4)

Cargo.toml

@@ -10,3 +10,4 @@ repository = "https://github.com/scouten/asciidoc-parser"
 rust-version = "1.72.0"
 
 [dependencies]
+nom = "7.1"

src/lib.rs

@@ -5,6 +5,7 @@
 #![deny(warnings)]
 #![doc = include_str!("../README.md")]
 
+pub(crate) mod primitives;
 pub mod strings;
 
 #[cfg(test)]

src/primitives/line.rs

@@ -0,0 +1,26 @@
+use nom::{bytes::complete::take_till, IResult};
+
+#[allow(dead_code)] // TEMPORARY
+pub(crate) fn line(input: &str) -> IResult<&str, &str> {
+    take_till(|c| c == '\n')(input)
+        .map(|ri| trim_rem_start_matches(ri, '\n'))
+        .map(|ri| trim_rem_end_matches(ri, '\r'))
+}
+
+#[allow(dead_code)] // TEMPORARY
+fn trim_rem_start_matches<'a>(rem_inp: (&'a str, &'a str), c: char) -> (&'a str, &'a str) {
+    if let Some(rem) = rem_inp.0.strip_prefix(c) {
+        (rem, rem_inp.1)
+    } else {
+        rem_inp
+    }
+}
+
+#[allow(dead_code)] // TEMPORARY
+fn trim_rem_end_matches<'a>(rem_inp: (&'a str, &'a str), c: char) -> (&'a str, &'a str) {
+    if let Some(inp) = rem_inp.1.strip_suffix(c) {
+        (rem_inp.0, inp)
+    } else {
+        rem_inp
+    }
+}

src/primitives/mod.rs

@@ -0,0 +1,6 @@
+//! Contains various primitive parsing routines.
+//! Not part of the public API surface.
+
+mod line;
+#[allow(unused_imports)]
+pub(crate) use line::line;

src/tests/mod.rs

@@ -6,4 +6,5 @@
 #![allow(clippy::unwrap_used)]
 
 mod fixtures;
+mod primitives;
 mod strings;

src/tests/primitives/line.rs

@@ -0,0 +1,37 @@
+mod fn_line {
+    use crate::primitives::line;
+
+    #[test]
+    fn empty_source() {
+        assert_eq!(line(""), Ok(("", "")));
+    }
+
+    #[test]
+    fn simple_line() {
+        assert_eq!(line("abc"), Ok(("", "abc")));
+    }
+
+    #[test]
+    fn consumes_lf() {
+        // Should consume but not return \n.
+        assert_eq!(line("abc\ndef"), Ok(("def", "abc")));
+    }
+
+    #[test]
+    fn consumes_crlf() {
+        // Should consume but not return \r\n.
+        assert_eq!(line("abc\r\ndef"), Ok(("def", "abc")));
+    }
+
+    #[test]
+    fn doesnt_consume_lfcr() {
+        // Should consume \n but not a subsequent \r.
+        assert_eq!(line("abc\n\rdef"), Ok(("\rdef", "abc")));
+    }
+
+    #[test]
+    fn doesnt_consume_standalone_cr() {
+        // Shouldn't terminate line at \r without \n.
+        assert_eq!(line("abc\rdef"), Ok(("", "abc\rdef")));
+    }
+}

src/tests/primitives/mod.rs

@@ -0,0 +1 @@
+mod line;