From 3c3f4943cbbda350a26e82f4b33ace36c4b1f038 Mon Sep 17 00:00:00 2001
From: Eric Scouten <git@scouten.me>
Date: Sun, 10 Dec 2023 18:10:36 -0800
Subject: [PATCH] Add primitive parser for normalized, non-empty line (#6)

---
 src/primitives/line.rs       | 35 ++++++++++++++++++-
 src/primitives/mod.rs        |  2 +-
 src/tests/primitives/line.rs | 66 ++++++++++++++++++++++++++++++++++++
 3 files changed, 101 insertions(+), 2 deletions(-)

diff --git a/src/primitives/line.rs b/src/primitives/line.rs
index db2bcec..07f8da2 100644
--- a/src/primitives/line.rs
+++ b/src/primitives/line.rs
@@ -1,4 +1,7 @@
-use nom::{bytes::complete::take_till, IResult};
+use nom::{
+    bytes::complete::{take_till, take_till1},
+    IResult,
+};
 
 /// Return a single line from the source.
 ///
@@ -27,6 +30,36 @@ pub(crate) fn normalized_line(input: &str) -> IResult<&str, &str> {
         .map(trim_trailing_spaces)
 }
 
+/// Return a single _normalized, non-empty_ line from the source.
+///
+/// A line is terminated by end-of-input or a single `\n` character
+/// or a single `\r\n` sequence. The end of line sequence is consumed
+/// but not included in the returned line.
+///
+/// All trailing spaces are removed from the line.
+///
+/// Returns an error if the line becomes empty after trailing spaces have been
+/// removed.
+#[allow(dead_code)] // TEMPORARY
+pub(crate) fn non_empty_line(input: &str) -> IResult<&str, &str> {
+    use nom::{
+        error::{Error, ErrorKind},
+        Err,
+    };
+
+    take_till1(|c| c == '\n')(input)
+        .map(|ri| trim_rem_start_matches(ri, '\n'))
+        .map(|ri| trim_rem_end_matches(ri, '\r'))
+        .map(trim_trailing_spaces)
+        .and_then(|(rem, inp)| {
+            if inp.is_empty() {
+                Err(Err::Error(Error::new(input, ErrorKind::TakeTill1)))
+            } else {
+                Ok((rem, inp))
+            }
+        })
+}
+
 #[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) {
diff --git a/src/primitives/mod.rs b/src/primitives/mod.rs
index e91fe93..afeadd7 100644
--- a/src/primitives/mod.rs
+++ b/src/primitives/mod.rs
@@ -3,4 +3,4 @@
 
 mod line;
 #[allow(unused_imports)]
-pub(crate) use line::{line, normalized_line};
+pub(crate) use line::{line, non_empty_line, normalized_line};
diff --git a/src/tests/primitives/line.rs b/src/tests/primitives/line.rs
index 922f3b3..9d92834 100644
--- a/src/tests/primitives/line.rs
+++ b/src/tests/primitives/line.rs
@@ -88,3 +88,69 @@ mod normalized_line {
         assert_eq!(normalized_line("abc\rdef"), Ok(("", "abc\rdef")));
     }
 }
+
+mod non_empty_line {
+    use nom::{
+        error::{Error, ErrorKind},
+        Err,
+    };
+
+    use crate::primitives::non_empty_line;
+
+    #[test]
+    fn empty_source() {
+        let expected_err: Err<Error<&str>> = Err::Error(Error::new("", ErrorKind::TakeTill1));
+
+        let actual_err = non_empty_line("").unwrap_err();
+
+        assert_eq!(expected_err, actual_err);
+    }
+
+    #[test]
+    fn only_spaces() {
+        let expected_err: Err<Error<&str>> = Err::Error(Error::new("   ", ErrorKind::TakeTill1));
+
+        let actual_err = non_empty_line("   ").unwrap_err();
+
+        assert_eq!(expected_err, actual_err);
+    }
+
+    #[test]
+    fn simple_line() {
+        assert_eq!(non_empty_line("abc"), Ok(("", "abc")));
+    }
+
+    #[test]
+    fn trailing_space() {
+        assert_eq!(non_empty_line("abc "), Ok(("", "abc")));
+    }
+
+    #[test]
+    fn trailing_spaces() {
+        assert_eq!(non_empty_line("abc   "), Ok(("", "abc")));
+    }
+
+    #[test]
+    fn consumes_lf() {
+        // Should consume but not return \n.
+        assert_eq!(non_empty_line("abc  \ndef"), Ok(("def", "abc")));
+    }
+
+    #[test]
+    fn consumes_crlf() {
+        // Should consume but not return \r\n.
+        assert_eq!(non_empty_line("abc\r\ndef"), Ok(("def", "abc")));
+    }
+
+    #[test]
+    fn doesnt_consume_lfcr() {
+        // Should consume \n but not a subsequent \r.
+        assert_eq!(non_empty_line("abc\n\rdef"), Ok(("\rdef", "abc")));
+    }
+
+    #[test]
+    fn doesnt_consume_standalone_cr() {
+        // Shouldn't terminate non_empty_line at \r without \n.
+        assert_eq!(non_empty_line("abc\rdef"), Ok(("", "abc\rdef")));
+    }
+}