fix(tvix/eval): ensure disassembler prints continous lines correctly r/4767

There can be different spans on the same line, so the previous
implementation would duplicate line numbers unnecessarily.

Change-Id: I8d8db77177aee0d834a6ec3584641e1bd5f31c3e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6434
Reviewed-by: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI

2 files changed, 12 insertions, 4 deletions

diff --git a/tvix/eval/src/chunk.rs b/tvix/eval/src/chunk.rs
index defa409f18..c89e6ef848 100644
--- a/tvix/eval/src/chunk.rs
+++ b/tvix/eval/src/chunk.rs
@@ -77,4 +77,13 @@ impl Chunk {
 
         panic!("compiler error: chunk missing span for offset {}", offset.0);
     }
+
+    /// Retrieve the line from which the instruction at `offset` was
+    /// compiled. Only available when the chunk carries a codemap,
+    /// i.e. when the disassembler is enabled.
+    #[cfg(feature = "disassembler")]
+    pub fn get_line(&self, offset: CodeIdx) -> usize {
+        let span = self.get_span(offset);
+        self.codemap.look_up_span(span).begin.line + 1
+    }
 }
diff --git a/tvix/eval/src/disassembler.rs b/tvix/eval/src/disassembler.rs
index b089797f8a..7948977e4b 100644
--- a/tvix/eval/src/disassembler.rs
+++ b/tvix/eval/src/disassembler.rs
@@ -44,13 +44,12 @@ impl Drop for Tracer {
 fn disassemble_op(tw: &mut TabWriter<Stderr>, chunk: &Chunk, width: usize, offset: usize) {
     let _ = write!(tw, "{:0width$}\t ", offset, width = width);
 
-    let span = chunk.get_span(CodeIdx(offset));
+    let line = chunk.get_line(CodeIdx(offset));
 
-    if offset > 0 && chunk.get_span(CodeIdx(offset - 1)) == span {
+    if offset > 0 && chunk.get_line(CodeIdx(offset - 1)) == line {
         write!(tw, "   |\t").unwrap();
     } else {
-        let loc = chunk.codemap.look_up_span(span);
-        write!(tw, "{:4}\t", loc.begin.line + 1).unwrap();
+        write!(tw, "{:4}\t", line).unwrap();
     }
 
     let _ = match chunk.code[offset] {