fix(debugger): crash when stepping through locations spanning multipl…

…e lines (#3920)

# Description

The debugger REPL was failing under certain scenarios when a stepped
location spanned multiple lines. We tracked down the failure to a
missing bounds check.

This PR fixes the issue, introduces a refactor to make the relevant code
testable, and adds regression tests to prevent reoccurrence.

This PR is best reviewed as a whole instead of commit-by-commit.

## Summary

- Moves source code printing logic from the main debugger REPL module,
to a new source_code_printer module.
- Decouples actual printing from rendering logic to improve testability.
- Adds regression tests

## Documentation

Check one:
- [ ] No documentation needed.
- [x] Documentation included in this PR.
- [ ] **[Exceptional Case]** Documentation to be submitted in a separate
PR.

# PR Checklist\*

- [x] I have tested the changes locally.
- [x] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.

tooling/debugger/Cargo.toml

@@ -20,4 +20,7 @@ codespan-reporting.workspace = true
 dap.workspace = true
 easy-repl = "0.2.1"
 owo-colors = "3"
-serde_json.workspace = true
+serde_json.workspace = true
+
+[dev_dependencies]
+tempfile.workspace = true

tooling/debugger/src/lib.rs

@@ -1,6 +1,7 @@
 mod context;
 mod dap;
 mod repl;
+mod source_code_printer;
 
 use std::io::{Read, Write};
 

tooling/debugger/src/repl.rs

@@ -9,12 +9,7 @@ use nargo::{artifacts::debug::DebugArtifact, ops::DefaultForeignCallExecutor, Na
 use easy_repl::{command, CommandStatus, Repl};
 use std::cell::RefCell;
 
-use codespan_reporting::files::Files;
-use noirc_errors::Location;
-
-use owo_colors::OwoColorize;
-
-use std::ops::Range;
+use crate::source_code_printer::print_source_code_location;
 
 pub struct ReplDebugger<'a, B: BlackBoxFunctionSolver> {
     context: DebugContext<'a, B>,
@@ -70,73 +65,7 @@ impl<'a, B: BlackBoxFunctionSolver> ReplDebugger<'a, B> {
                         );
                     }
                 }
-                self.show_source_code_location(&location);
-            }
-        }
-    }
-
-    fn print_location_path(&self, loc: Location) {
-        let line_number = self.debug_artifact.location_line_number(loc).unwrap();
-        let column_number = self.debug_artifact.location_column_number(loc).unwrap();
-
-        println!(
-            "At {}:{line_number}:{column_number}",
-            self.debug_artifact.name(loc.file).unwrap()
-        );
-    }
-
-    fn show_source_code_location(&self, location: &OpcodeLocation) {
-        let locations = self.debug_artifact.debug_symbols[0].opcode_location(location);
-        let Some(locations) = locations else { return };
-        for loc in locations {
-            self.print_location_path(loc);
-
-            let loc_line_index = self.debug_artifact.location_line_index(loc).unwrap();
-
-            // How many lines before or after the location's line we
-            // print
-            let context_lines = 5;
-
-            let first_line_to_print =
-                if loc_line_index < context_lines { 0 } else { loc_line_index - context_lines };
-
-            let last_line_index = self.debug_artifact.last_line_index(loc).unwrap();
-            let last_line_to_print = std::cmp::min(loc_line_index + context_lines, last_line_index);
-
-            let source = self.debug_artifact.location_source_code(loc).unwrap();
-            for (current_line_index, line) in source.lines().enumerate() {
-                let current_line_number = current_line_index + 1;
-
-                if current_line_index < first_line_to_print {
-                    // Ignore lines before range starts
-                    continue;
-                } else if current_line_index == first_line_to_print && current_line_index > 0 {
-                    // Denote that there's more lines before but we're not showing them
-                    print_line_of_ellipsis(current_line_index);
-                }
-
-                if current_line_index > last_line_to_print {
-                    // Denote that there's more lines after but we're not showing them,
-                    // and stop printing
-                    print_line_of_ellipsis(current_line_number);
-                    break;
-                }
-
-                if current_line_index == loc_line_index {
-                    // Highlight current location
-                    let Range { start: loc_start, end: loc_end } =
-                        self.debug_artifact.location_in_line(loc).unwrap();
-                    println!(
-                        "{:>3} {:2} {}{}{}",
-                        current_line_number,
-                        "->",
-                        &line[0..loc_start].to_string().dimmed(),
-                        &line[loc_start..loc_end],
-                        &line[loc_end..].to_string().dimmed()
-                    );
-                } else {
-                    print_dimmed_line(current_line_number, line);
-                }
+                print_source_code_location(self.debug_artifact, &location);
             }
         }
     }
@@ -384,14 +313,6 @@ impl<'a, B: BlackBoxFunctionSolver> ReplDebugger<'a, B> {
     }
 }
 
-fn print_line_of_ellipsis(line_number: usize) {
-    println!("{}", format!("{:>3} {}", line_number, "...").dimmed());
-}
-
-fn print_dimmed_line(line_number: usize, line: &str) {
-    println!("{}", format!("{:>3} {:2} {}", line_number, "", line).dimmed());
-}
-
 pub fn run<B: BlackBoxFunctionSolver>(
     blackbox_solver: &B,
     circuit: &Circuit,