diff --git a/src/parse_tree.rs b/src/parse_tree.rs
index cac3c5414..eae46c362 100644
--- a/src/parse_tree.rs
+++ b/src/parse_tree.rs
@@ -12,6 +12,7 @@ use crate::parse_constants::{
 };
 use crate::tokenizer::TokenizerError;
 use crate::wchar::prelude::*;
+use crate::wcstringutil::count_newlines;
 
 /// A struct representing the token type that we use internally.
 #[derive(Clone, Copy)]
@@ -114,6 +115,16 @@ impl ParsedSource {
     pub fn new(src: WString, ast: Ast) -> Self {
         ParsedSource { src, ast }
     }
+
+    // Return a line counter over this source.
+    pub fn line_counter<NodeType: Node>(self: &Arc<Self>) -> LineCounter<NodeType> {
+        LineCounter {
+            parsed_source: Pin::new(Arc::clone(self)),
+            node: std::ptr::null(),
+            cached_offset: 0,
+            cached_count: 0,
+        }
+    }
 }
 
 pub type ParsedSourceRef = Arc<ParsedSource>;
@@ -182,3 +193,78 @@ pub fn parse_source(
         Some(Arc::new(ParsedSource::new(src, ast)))
     }
 }
+
+/// A type which assists in returning line numbers.
+/// This is a somewhat strange type which both counts line numbers and also holds
+/// a reference to a "current" node; this matches the expected usage from parse_execution.
+pub struct LineCounter<NodeType: Node> {
+    /// The parse tree containing the node.
+    /// This is pinned because we hold a pointer into it.
+    parsed_source: Pin<Arc<ParsedSource>>,
+
+    /// The node itself. This points into the parsed source, or it may be null.
+    node: *const NodeType,
+
+    // Cached line number information: the line number of the start of the node, and the number of newlines.
+    cached_offset: usize,
+    cached_count: usize,
+}
+
+impl<NodeType: Node> LineCounter<NodeType> {
+    // Return a line counter for empty source.
+    pub fn empty() -> Self {
+        let parsed_source =
+            Pin::new(parse_source(WString::new(), ParseTreeFlags::default(), None).unwrap());
+        LineCounter {
+            parsed_source,
+            node: std::ptr::null(),
+            cached_offset: 0,
+            cached_count: 0,
+        }
+    }
+
+    // Count the number of newlines, leveraging our cache.
+    pub fn line_offset_of_character_at_offset(&mut self, offset: usize) -> usize {
+        let src = &self.parsed_source.src;
+        assert!(offset <= src.len());
+
+        // Easy hack to handle 0.
+        if offset == 0 {
+            return 0;
+        }
+
+        // We want to return the number of newlines at offsets less than the given offset.
+        if offset > self.cached_offset {
+            // Add one for every newline we find in the range [cached_offset, offset).
+            // The codegen is substantially better when using a char slice than the char iterator.
+            self.cached_count += count_newlines(&src[self.cached_offset..offset]);
+        } else if offset < self.cached_offset {
+            // Subtract one for every newline we find in the range [offset, cached_range.start).
+            self.cached_count -= count_newlines(&src[offset..self.cached_offset]);
+        }
+        self.cached_offset = offset;
+        self.cached_count
+    }
+
+    // Returns the 0-based line number of the node.
+    pub fn line_offset_of_node(&mut self) -> Option<usize> {
+        let src_offset = self.source_offset_of_node()?;
+        Some(self.line_offset_of_character_at_offset(src_offset))
+    }
+
+    // Return the 0 based character offset of the node.
+    pub fn source_offset_of_node(&mut self) -> Option<usize> {
+        // Safety: any node is valid for the lifetime of the source.
+        let node = unsafe { self.node.as_ref()? };
+        let range = node.try_source_range()?;
+        Some(range.start())
+    }
+
+    // Set the node. The node must belong to the parsed source.
+    // Returns the original node.
+    pub fn set_node<'a>(&mut self, node: Option<&'a NodeType>) -> Option<&'a NodeType> {
+        let node_ptr = node.map_or(std::ptr::null(), |node| node);
+        let prev = std::mem::replace(&mut self.node, node_ptr);
+        unsafe { prev.as_ref() }
+    }
+}
diff --git a/src/tests/parser.rs b/src/tests/parser.rs
index f8ed04a17..9611de929 100644
--- a/src/tests/parser.rs
+++ b/src/tests/parser.rs
@@ -1,4 +1,4 @@
-use crate::ast::{self, Ast, List, Node, Traversal};
+use crate::ast::{self, Ast, JobPipeline, List, Node, Traversal};
 use crate::common::ScopeGuard;
 use crate::env::EnvStack;
 use crate::expand::ExpandFlags;
@@ -6,6 +6,7 @@ use crate::io::{IoBufferfill, IoChain};
 use crate::parse_constants::{
     ParseErrorCode, ParseTreeFlags, ParserTestErrorBits, StatementDecoration,
 };
+use crate::parse_tree::{parse_source, LineCounter};
 use crate::parse_util::{parse_util_detect_errors, parse_util_detect_errors_in_argument};
 use crate::parser::{CancelBehavior, Parser};
 use crate::reader::{reader_pop, reader_push, reader_reset_interrupted, ReaderConfig};
@@ -747,3 +748,74 @@ fn test_cancellation() {
     reader_reset_interrupted();
     signal_clear_cancel();
 }
+
+#[test]
+fn test_line_counter() {
+    let src = L!("echo line1; echo still_line_1;\n\necho line3");
+    let ps = parse_source(src.to_owned(), ParseTreeFlags::default(), None)
+        .expect("Failed to parse source");
+    assert!(!ps.ast.errored());
+    let mut line_counter = ps.line_counter();
+
+    // Test line_offset_of_character_at_offset, both forwards and backwards to exercise the cache.
+    let mut expected = 0;
+    for (idx, c) in src.chars().enumerate() {
+        let line_offset = line_counter.line_offset_of_character_at_offset(idx);
+        assert_eq!(line_offset, expected);
+        if c == '\n' {
+            expected += 1;
+        }
+    }
+    for (idx, c) in src.chars().enumerate().rev() {
+        if c == '\n' {
+            expected -= 1;
+        }
+        let line_offset = line_counter.line_offset_of_character_at_offset(idx);
+        assert_eq!(line_offset, expected);
+    }
+
+    fn ref_eq<T>(a: Option<&T>, b: Option<&T>) -> bool {
+        match (a, b) {
+            (Some(a), Some(b)) => std::ptr::eq(a, b),
+            (None, None) => true,
+            _ => false,
+        }
+    }
+
+    let pipelines: Vec<_> = ps.ast.walk().filter_map(|n| n.as_job_pipeline()).collect();
+    assert_eq!(pipelines.len(), 3);
+    let src_offsets = [0, 0, 2];
+    assert_eq!(line_counter.source_offset_of_node(), None);
+    assert_eq!(line_counter.line_offset_of_node(), None);
+
+    let mut last_set = None;
+    for (idx, &node) in pipelines.iter().enumerate() {
+        let orig = line_counter.set_node(Some(node));
+        assert!(ref_eq(orig, last_set));
+        last_set = Some(node);
+        assert_eq!(
+            line_counter.source_offset_of_node(),
+            Some(node.source_range().start())
+        );
+        assert_eq!(line_counter.line_offset_of_node(), Some(src_offsets[idx]));
+    }
+
+    for (idx, &node) in pipelines.iter().enumerate().rev() {
+        let orig = line_counter.set_node(Some(node));
+        assert!(ref_eq(orig, last_set));
+        last_set = Some(node);
+        assert_eq!(
+            line_counter.source_offset_of_node(),
+            Some(node.source_range().start())
+        );
+        assert_eq!(line_counter.line_offset_of_node(), Some(src_offsets[idx]));
+    }
+}
+
+#[test]
+fn test_line_counter_empty() {
+    let mut line_counter = LineCounter::<JobPipeline>::empty();
+    assert_eq!(line_counter.line_offset_of_character_at_offset(0), 0);
+    assert_eq!(line_counter.line_offset_of_node(), None);
+    assert_eq!(line_counter.source_offset_of_node(), None);
+}