conflicts: encode unmaterializeable lines

Fixes jj-vcs#3968

Fixes jj-vcs#3975

CHANGELOG.md

@@ -35,6 +35,14 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 * Error on `trunk()` revset resolution is now handled gracefully.
   [#4616](https://github.com/martinvonz/jj/issues/4616)
 
+* Conflicts involving non-empty files that do not end in a newline no longer
+  look broken when materialized.
+  [#3968](https://github.com/martinvonz/jj/issues/3968)
+
+* Conflicts involving sides that themselves contain conflict markers can now be
+  materialized in a way that `jj` can parse correctly.
+  [#3975](https://github.com/martinvonz/jj/issues/3968)
+
 ## [0.22.0] - 2024-10-02
 
 ### Breaking changes
@@ -370,7 +378,7 @@ Thanks to the people who made this release happen!
 * Vladimír Čunát (@vcunat)
 * Vladimir (@0xdeafbeef)
 * Yuya Nishihara (@yuja)
-
+  
 ## [0.19.0] - 2024-07-03
 
 ### Breaking changes

lib/src/conflicts.rs

@@ -19,6 +19,7 @@ use std::io::Write;
 use std::iter::zip;
 
 use bstr::BString;
+use bstr::ByteVec;
 use futures::stream::BoxStream;
 use futures::try_join;
 use futures::Stream;
@@ -71,6 +72,12 @@ static CONFLICT_MARKER_REGEX: once_cell::sync::Lazy<Regex> = once_cell::sync::La
         .build()
         .unwrap()
 });
+static DIRECTIVE_LINE_REGEX: once_cell::sync::Lazy<Regex> = once_cell::sync::Lazy::new(|| {
+    RegexBuilder::new(r"^\\JJ")
+        .multi_line(true)
+        .build()
+        .unwrap()
+});
 
 fn write_diff_hunks(hunks: &[DiffHunk], file: &mut dyn Write) -> std::io::Result<()> {
     for hunk in hunks {
@@ -235,6 +242,11 @@ pub fn materialize_merge_result(
     single_hunk: Merge<BString>,
     output: &mut dyn Write,
 ) -> std::io::Result<()> {
+    let single_hunk = single_hunk.map_owned(|side| encode_unmaterializeable_lines(side.into()));
+
+    // From now on, we assume some invariants guaranteed by the encoding function
+    // above. See its docstring for details.
+
     let merge_result = files::merge(&single_hunk);
     match merge_result {
         MergeResult::Resolved(content) => {
@@ -393,7 +405,7 @@ pub fn parse_merge_result(input: &[u8], num_sides: usize) -> Option<Merge<BStrin
         }
     }
 
-    Some(result)
+    Some(result.map_owned(decode_materialized_side))
 }
 
 fn parse_conflict_into_list_of_hunks(
@@ -588,3 +600,109 @@ pub async fn update_from_content(
     };
     Ok(new_file_ids)
 }
+
+const JJ_NO_NEWLINE_AT_EOF: &[u8] = b"\n\\JJ: No newline at the end of file\n";
+const JJ_VERBATIM_LINE: &str = "\\JJ Verbatim Line:";
+static JJ_VERBATIM_LINE_REPLACEMENT: once_cell::sync::Lazy<Vec<u8>> =
+    once_cell::sync::Lazy::new(|| format!("{JJ_VERBATIM_LINE}$0").into_bytes());
+static VERBATIM_LINE_REGEX: once_cell::sync::Lazy<Regex> = once_cell::sync::Lazy::new(|| {
+    RegexBuilder::new(&format!("^{}", regex::escape(JJ_VERBATIM_LINE)))
+        .multi_line(true)
+        .build()
+        .unwrap()
+});
+
+/// Encode a side of a conflict to satisfy some invariants
+///
+/// - The result will not contain any conflict markers
+/// - The result will contain 0 or more newline-terminated lines. In other
+///   words, it is either empty or ends in a newline.
+///
+/// This transformation is reversible and it is hoped that the result is
+/// human-readable. See the tests below for examples.
+fn encode_unmaterializeable_lines(mut side: Vec<u8>) -> Vec<u8> {
+    replace_all_avoid_cloning(
+        &DIRECTIVE_LINE_REGEX,
+        &mut side,
+        JJ_VERBATIM_LINE_REPLACEMENT.as_slice(),
+    );
+    replace_all_avoid_cloning(
+        &CONFLICT_MARKER_REGEX,
+        &mut side,
+        JJ_VERBATIM_LINE_REPLACEMENT.as_slice(),
+    );
+    if !side.is_empty() && !side.ends_with(b"\n") {
+        side.push_str(JJ_NO_NEWLINE_AT_EOF);
+    }
+    side
+}
+
+/// Undo the transformation done by `encode_unmaterializeable_lines`
+fn decode_materialized_side(mut side: BString) -> BString {
+    if side.ends_with(JJ_NO_NEWLINE_AT_EOF) {
+        let len = side.len();
+        side.truncate(len - JJ_NO_NEWLINE_AT_EOF.len());
+    }
+    replace_all_avoid_cloning(&VERBATIM_LINE_REGEX, &mut side, b"");
+    side
+}
+
+fn replace_all_avoid_cloning(regex: &Regex, side: &mut Vec<u8>, replacement: &[u8]) {
+    // TODO(ilyagr): The optimization to avoid the clone in the common case
+    // might be premature. See also
+    // https://github.com/rust-lang/regex/issues/676 for other options. I like
+    // my proposal there in theory, but it would take work that I haven't done
+    // to make sure it works, and ideally it would be a crate.
+    if regex.is_match(side) {
+        *side = regex.replace_all(side, replacement).to_vec();
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use bstr::BString;
+    use indoc::indoc;
+
+    use super::{decode_materialized_side, encode_unmaterializeable_lines};
+
+    #[test]
+    fn test_conflict_side_encoding_and_decoding() {
+        let initial_text: BString = indoc! {br"
+        <<<<<<<
+        blahblah"}
+        .into();
+
+        let encoded_text: BString = encode_unmaterializeable_lines(initial_text.to_vec()).into();
+        insta::assert_snapshot!(encoded_text, @r###"
+        \JJ Verbatim Line:<<<<<<<
+        blahblah
+        \JJ: No newline at the end of file
+        "###);
+        assert_eq!(decode_materialized_side(encoded_text.clone()), initial_text);
+
+        let doubly_encoded_text: BString =
+            encode_unmaterializeable_lines(encoded_text.clone().into()).into();
+        insta::assert_snapshot!(doubly_encoded_text, @r###"
+        \JJ Verbatim Line:\JJ Verbatim Line:<<<<<<<
+        blahblah
+        \JJ Verbatim Line:\JJ: No newline at the end of file
+        "###);
+        // The above should (and does) decode to a file with a newline at the end
+        assert_eq!(decode_materialized_side(doubly_encoded_text), encoded_text);
+    }
+
+    #[test]
+    fn test_conflict_side_encoding_and_decoding2() {
+        let initial_text = br"\JJ: No newline at the end of file";
+
+        let encoded_text: BString = encode_unmaterializeable_lines(initial_text.to_vec()).into();
+        insta::assert_snapshot!(encoded_text, @r###"
+        \JJ Verbatim Line:\JJ: No newline at the end of file
+        \JJ: No newline at the end of file
+        "###);
+        assert_eq!(
+            decode_materialized_side(encoded_text.clone()),
+            BString::from(initial_text)
+        );
+    }
+}

lib/tests/test_conflicts.rs

@@ -327,6 +327,99 @@ fn test_materialize_parse_roundtrip() {
     "###);
 }
 
+// Important TODO (maybe not for this file): add a test of what happens when the
+// user removes conflict markers and runs `jj diff`
+
+#[test]
+fn test_materialize_parse_roundtrip_tricky() {
+    let test_repo = TestRepo::init();
+    let store = test_repo.repo.store();
+
+    let path = RepoPath::from_internal_string("file");
+    let base_id = testutils::write_file(
+        store,
+        path,
+        indoc! {"
+            \\JJ Verbatim Line: fake verbatim line
+            line 1
+            line 2 <<<<<<<
+            <<<<<<< line 3
+            line 4
+            line 5"},
+    );
+    let left_id = testutils::write_file(
+        store,
+        path,
+        indoc! {"
+            \\JJ Verbatim Line: fake verbatim line
+            line 1 left
+            line 2 left
+            <<<<<<<< line 3
+            line 4
+            line 5 left"},
+    );
+    let right_id = testutils::write_file(
+        store,
+        path,
+        indoc! {"
+            \\JJ Verbatim Line: fake verbatim line
+            line 1 right
+            line 2
+            line 3
+            line 4 right
+            line 5 right
+        "},
+    );
+
+    let conflict = Merge::from_removes_adds(
+        vec![Some(base_id.clone())],
+        vec![Some(left_id.clone()), Some(right_id.clone())],
+    );
+    let materialized = materialize_conflict_string(store, path, &conflict);
+    insta::assert_snapshot!(
+        materialized,
+        @r###"
+    \JJ Verbatim Line:\JJ Verbatim Line: fake verbatim line
+    <<<<<<< Conflict 1 of 1
+    %%%%%%% Changes from base to side #1
+    -line 1
+    -line 2 <<<<<<<
+    -\JJ Verbatim Line:<<<<<<< line 3
+    +line 1 left
+    +line 2 left
+    +<<<<<<<< line 3
+     line 4
+    -line 5
+    +line 5 left
+     \JJ: No newline at the end of file
+    +++++++ Contents of side #2
+    line 1 right
+    line 2
+    line 3
+    line 4 right
+    line 5 right
+    >>>>>>> Conflict 1 of 1 ends
+    "###
+    );
+
+    // The first add should always be from the left side
+    insta::assert_debug_snapshot!(
+        parse_merge_result(materialized.as_bytes(), conflict.num_sides()),
+        @r###"
+    Some(
+        Conflicted(
+            [
+                "\\JJ Verbatim Line: fake verbatim line\nline 1 left\nline 2 left\n<<<<<<<< line 3\nline 4\nline 5 left",
+                "\\JJ Verbatim Line: fake verbatim line\nline 1\nline 2 <<<<<<<\n<<<<<<< line 3\nline 4\nline 5",
+                "\\JJ Verbatim Line: fake verbatim line\nline 1 right\nline 2\nline 3\nline 4 right\nline 5 right\n",
+            ],
+        ),
+    )
+    "###);
+
+    // TODO: update_from_conflict?
+}
+
 #[test]
 fn test_materialize_conflict_no_newlines_at_eof() {
     let test_repo = TestRepo::init();
@@ -345,16 +438,29 @@ fn test_materialize_conflict_no_newlines_at_eof() {
     insta::assert_snapshot!(materialized,
         @r###"
     <<<<<<< Conflict 1 of 1
-    %%%%%%% Changes from base to side #1
-    -base+++++++ Contents of side #2
-    right>>>>>>> Conflict 1 of 1 ends
+    +++++++ Contents of side #1
+    %%%%%%% Changes from base to side #2
+    -base
+    +right
+     \JJ: No newline at the end of file
+    >>>>>>> Conflict 1 of 1 ends
     "###
     );
-    // BUG(#3968): These conflict markers cannot be parsed
+    // These conflict markers can be parsed (issue #3968)
     insta::assert_debug_snapshot!(parse_merge_result(
         materialized.as_bytes(),
         conflict.num_sides()
-    ),@"None");
+    ),@r###"
+    Some(
+        Conflicted(
+            [
+                "",
+                "base",
+                "right",
+            ],
+        ),
+    )
+    "###);
 }
 
 #[test]