Add Lua bindings for SpanCalculator

This one is fun, because `SpanCalculator` holds a reference to the
file's source code, while the `mlua::UserData` works best for Rust types
that are 'static.

To get around this, we make sure to only ever create `SpanCalculator`
wrappers for source data that is owned by the Lua interpreter, and add
that source data as a user value of the Lua wrapper that we create.
That should cause Lua's garbage collector to ensure that the source code
outlives the `SpanCalculator`, making it safe for us to transmute the
source reference to a 'static lifetime.

lsp-positions/Cargo.toml

@@ -18,13 +18,19 @@ test = false
 
 [features]
 bincode = ["dep:bincode"]
-lua = ["dep:mlua"]
+lua = ["tree-sitter", "dep:mlua", "dep:mlua-tree-sitter"]
 tree-sitter = ["dep:tree-sitter"]
 
 [dependencies]
 memchr = "2.4"
 mlua = { version = "0.9", optional = true }
+mlua-tree-sitter = { version = "0.1", git="https://github.com/dcreager/mlua-tree-sitter", optional = true }
 tree-sitter = { version=">= 0.19", optional=true }
 unicode-segmentation = { version="1.8" }
 serde = { version="1", optional=true, features=["derive"] }
 bincode = { version="2.0.0-rc.3", optional=true }
+
+[dev-dependencies]
+anyhow = { version = "1.0" }
+lua-helpers = { path = "../lua-helpers" }
+tree-sitter-python = { version = "0.19.1" }

lsp-positions/src/lib.rs

@@ -34,7 +34,7 @@ use memchr::memchr;
 use unicode_segmentation::UnicodeSegmentation as _;
 
 #[cfg(feature = "lua")]
-mod lua;
+pub mod lua;
 
 fn grapheme_len(string: &str) -> usize {
     string.graphemes(true).count()

lsp-positions/src/lua.rs

@@ -11,11 +11,63 @@ use mlua::Error;
 use mlua::FromLua;
 use mlua::IntoLua;
 use mlua::Lua;
+use mlua::UserData;
+use mlua::UserDataMethods;
 use mlua::Value;
+use mlua_tree_sitter::TSNode;
+use mlua_tree_sitter::TreeWithSource;
 
 use crate::Offset;
 use crate::Position;
 use crate::Span;
+use crate::SpanCalculator;
+
+/// An extension trait that lets you load the `lsp_positions` module into a Lua environment.
+pub trait Module {
+    /// Loads the `lsp_positions` module into a Lua environment.
+    fn open_lsp_positions(&self) -> Result<(), mlua::Error>;
+}
+
+impl Module for Lua {
+    fn open_lsp_positions(&self) -> Result<(), mlua::Error> {
+        let exports = self.create_table()?;
+        let sc_type = self.create_table()?;
+
+        let function = self.create_function(|lua, source_value: mlua::String| {
+            // We are going to add the Lua string as a user value of the SpanCalculator's Lua
+            // wrapper.  That will ensure that the string is not garbage collected before the
+            // SpanCalculator, which makes it safe to transmute into a 'static reference.
+            let source = source_value.to_str()?;
+            let source: &'static str = unsafe { std::mem::transmute(source) };
+            let sc = SpanCalculator::new(source);
+            let sc = lua.create_userdata(sc)?;
+            sc.set_user_value(source_value)?;
+            Ok(sc)
+        })?;
+        sc_type.set("new", function)?;
+
+        #[cfg(feature = "tree-sitter")]
+        {
+            let function = self.create_function(|lua, tws_value: Value| {
+                // We are going to add the tree-sitter treee as a user value of the
+                // SpanCalculator's Lua wrapper.  That will ensure that the tree is not garbage
+                // collected before the SpanCalculator, which makes it safe to transmute into a
+                // 'static reference.
+                let tws = TreeWithSource::from_lua(tws_value.clone(), lua)?;
+                let source: &'static str = unsafe { std::mem::transmute(tws.src) };
+                let sc = SpanCalculator::new(source);
+                let sc = lua.create_userdata(sc)?;
+                sc.set_user_value(tws_value)?;
+                Ok(sc)
+            })?;
+            sc_type.set("new_from_tree", function)?;
+        }
+
+        exports.set("SpanCalculator", sc_type)?;
+        self.globals().set("lsp_positions", exports)?;
+        Ok(())
+    }
+}
 
 impl<'lua> FromLua<'lua> for Offset {
     fn from_lua(value: Value<'lua>, _: &'lua Lua) -> Result<Self, Error> {
@@ -142,3 +194,24 @@ impl<'lua> IntoLua<'lua> for Span {
         Ok(Value::Table(result))
     }
 }
+
+impl UserData for SpanCalculator<'static> {
+    fn add_methods<'lua, M: UserDataMethods<'lua, Self>>(methods: &mut M) {
+        methods.add_method_mut(
+            "for_line_and_column",
+            |_, sc, (line, line_utf8_offset, column_utf8_offset)| {
+                Ok(sc.for_line_and_column(line, line_utf8_offset, column_utf8_offset))
+            },
+        );
+
+        methods.add_method_mut(
+            "for_line_and_grapheme",
+            |_, sc, (line, line_utf8_offset, column_grapheme_offset)| {
+                Ok(sc.for_line_and_grapheme(line, line_utf8_offset, column_grapheme_offset))
+            },
+        );
+
+        #[cfg(feature = "tree-sitter")]
+        methods.add_method_mut("for_node", |_, sc, node: TSNode| Ok(sc.for_node(&node)));
+    }
+}

lsp-positions/tests/it/lua.rs

@@ -0,0 +1,88 @@
+// -*- coding: utf-8 -*-
+// ------------------------------------------------------------------------------------------------
+// Copyright © 2023, stack-graphs authors.
+// Licensed under either of Apache License, Version 2.0, or MIT license, at your option.
+// Please see the LICENSE-APACHE or LICENSE-MIT files in this distribution for license details.
+// ------------------------------------------------------------------------------------------------
+
+use lsp_positions::lua::Module;
+use lua_helpers::new_lua;
+use lua_helpers::CheckLua;
+
+#[test]
+fn can_calculate_positions_from_lua() -> Result<(), mlua::Error> {
+    let l = new_lua()?;
+    l.open_lsp_positions()?;
+    l.check(
+        r#"
+          local source = "   from a import *   "
+          local sc = lsp_positions.SpanCalculator.new(source)
+          local position = sc:for_line_and_column(0, 0, 9)
+          local expected = {
+            line=0,
+            column={
+              utf8_offset=9,
+              utf16_offset=9,
+              grapheme_offset=9,
+            },
+            containing_line={start=0, ["end"]=21},
+            trimmed_line={start=3, ["end"]=18},
+          }
+          assert_deepeq("position", expected, position)
+        "#,
+    )?;
+    Ok(())
+}
+
+#[cfg(feature = "tree-sitter")]
+#[test]
+fn can_calculate_tree_sitter_spans_from_lua() -> Result<(), anyhow::Error> {
+    let code = br#"
+      def double(x):
+          return x * 2
+    "#;
+    let mut parser = tree_sitter::Parser::new();
+    parser.set_language(tree_sitter_python::language()).unwrap();
+    let parsed = parser.parse(code, None).unwrap();
+
+    use mlua_tree_sitter::Module;
+    use mlua_tree_sitter::WithSource;
+    let l = new_lua()?;
+    l.open_lsp_positions()?;
+    l.open_ltreesitter()?;
+    l.globals().set("parsed", parsed.with_source(code))?;
+
+    l.check(
+        r#"
+          local module = parsed:root()
+          local double = module:child(0)
+          local name = double:child_by_field_name("name")
+          local sc = lsp_positions.SpanCalculator.new_from_tree(parsed)
+          local position = sc:for_node(name)
+          local expected = {
+            start={
+              line=1,
+              column={
+                utf8_offset=10,
+                utf16_offset=10,
+                grapheme_offset=10,
+              },
+              containing_line={start=1, ["end"]=21},
+              trimmed_line={start=7, ["end"]=21},
+            },
+            ["end"]={
+              line=1,
+              column={
+                utf8_offset=16,
+                utf16_offset=16,
+                grapheme_offset=16,
+              },
+              containing_line={start=1, ["end"]=21},
+              trimmed_line={start=7, ["end"]=21},
+            },
+          }
+          assert_deepeq("position", expected, position)
+        "#,
+    )?;
+    Ok(())
+}

lsp-positions/tests/it/main.rs

@@ -9,6 +9,9 @@ use unicode_segmentation::UnicodeSegmentation as _;
 
 use lsp_positions::Offset;
 
+#[cfg(feature = "lua")]
+mod lua;
+
 fn check_offsets(line: &str) {
     let offsets = Offset::all_chars(line).collect::<Vec<_>>();
     assert!(!offsets.is_empty());