Indentation rework (#1562)

* WIP: Rework indentation system

* Add ComplexNode for context-aware indentation (including a proof of concept for assignment statements in rust)

* Add switch statements to Go indents.toml (fixes the second half of issue #1523)
Remove commented-out code

* Migrate all existing indentation queries.
Add more options to ComplexNode and use them to improve C/C++ indentation.

* Add comments & replace Option<Vec<_>> with Vec<_>

* Add more detailed documentation for tree-sitter indentation

* Improve code style in indent.rs

* Use tree-sitter queries for indentation instead of TOML config.
Migrate existing indent queries.

* Add documentation for the new indent queries.
Change xtask docgen to look for indents.scm instead of indents.toml

* Improve code style in indent.rs.
Fix an issue with the rust indent query.

* Move indentation test sources to separate files.
Add `#not-kind-eq?`, `#same-line?` and `#not-same-line` custom predicates.
Improve the rust and c indent queries.

* Fix indent test.
Improve rust indent queries.

* Move indentation tests to integration test folder.

* Improve code style in indent.rs.
Reuse tree-sitter cursors for indentation queries.

* Migrate HCL indent query

* Replace custom loading in indent tests with a designated languages.toml

* Update indent query file name for --health command.

* Fix single-space formatting in indent queries.

* Add explanation for unwrapping.

Co-authored-by: Triton171 <triton0171@gmail.com>

6 files changed, 571 insertions, 241 deletions

diff --git a/helix-core/src/indent.rs b/helix-core/src/indent.rs
index 30f4a340..529139b8 100644
--- a/helix-core/src/indent.rs
+++ b/helix-core/src/indent.rs
@@ -1,6 +1,10 @@
+use std::collections::HashMap;
+
+use tree_sitter::{Query, QueryCursor, QueryPredicateArg};
+
 use crate::{
     chars::{char_is_line_ending, char_is_whitespace},
-    syntax::{IndentQuery, LanguageConfiguration, Syntax},
+    syntax::{LanguageConfiguration, RopeProvider, Syntax},
     tree_sitter::Node,
     Rope, RopeSlice,
 };
@@ -186,103 +190,405 @@ pub fn indent_level_for_line(line: RopeSlice, tab_width: usize) -> usize {
     len / tab_width
 }
 
-/// Find the highest syntax node at position.
-/// This is to identify the column where this node (e.g., an HTML closing tag) ends.
-fn get_highest_syntax_node_at_bytepos(syntax: &Syntax, pos: usize) -> Option<Node> {
-    let tree = syntax.tree();
-
-    // named_descendant
-    let mut node = tree.root_node().descendant_for_byte_range(pos, pos)?;
-
-    while let Some(parent) = node.parent() {
-        if parent.start_byte() == node.start_byte() {
-            node = parent
+/// Computes for node and all ancestors whether they are the first node on their line.
+/// The first entry in the return value represents the root node, the last one the node itself
+fn get_first_in_line(mut node: Node, byte_pos: usize, new_line: bool) -> Vec<bool> {
+    let mut first_in_line = Vec::new();
+    loop {
+        if let Some(prev) = node.prev_sibling() {
+            // If we insert a new line, the first node at/after the cursor is considered to be the first in its line
+            let first = prev.end_position().row != node.start_position().row
+                || (new_line && node.start_byte() >= byte_pos && prev.start_byte() < byte_pos);
+            first_in_line.push(Some(first));
+        } else {
+            // Nodes that have no previous siblings are first in their line if and only if their parent is
+            // (which we don't know yet)
+            first_in_line.push(None);
+        }
+        if let Some(parent) = node.parent() {
+            node = parent;
         } else {
             break;
         }
     }
 
-    Some(node)
+    let mut result = Vec::with_capacity(first_in_line.len());
+    let mut parent_is_first = true; // The root node is by definition the first node in its line
+    for first in first_in_line.into_iter().rev() {
+        if let Some(first) = first {
+            result.push(first);
+            parent_is_first = first;
+        } else {
+            result.push(parent_is_first);
+        }
+    }
+    result
 }
 
-/// Calculate the indentation at a given treesitter node.
-/// If newline is false, then any "indent" nodes on the line are ignored ("outdent" still applies).
-/// This is because the indentation is only increased starting at the second line of the node.
-fn calculate_indentation(
-    query: &IndentQuery,
-    node: Option<Node>,
-    line: usize,
-    newline: bool,
-) -> usize {
-    let mut increment: isize = 0;
-
-    let mut node = match node {
-        Some(node) => node,
-        None => return 0,
-    };
+/// The total indent for some line of code.
+/// This is usually constructed in one of 2 ways:
+/// - Successively add indent captures to get the (added) indent from a single line
+/// - Successively add the indent results for each line
+#[derive(Default)]
+struct Indentation {
+    /// The total indent (the number of indent levels) is defined as max(0, indent-outdent).
+    /// The string that this results in depends on the indent style (spaces or tabs, etc.)
+    indent: usize,
+    outdent: usize,
+}
+impl Indentation {
+    /// Add some other [IndentResult] to this.
+    /// The added indent should be the total added indent from one line
+    fn add_line(&mut self, added: &Indentation) {
+        if added.indent > 0 && added.outdent == 0 {
+            self.indent += 1;
+        } else if added.outdent > 0 && added.indent == 0 {
+            self.outdent += 1;
+        }
+    }
+    /// Add an indent capture to this indent.
+    /// All the captures that are added in this way should be on the same line.
+    fn add_capture(&mut self, added: IndentCaptureType) {
+        match added {
+            IndentCaptureType::Indent => {
+                self.indent = 1;
+            }
+            IndentCaptureType::Outdent => {
+                self.outdent = 1;
+            }
+        }
+    }
+    fn as_string(&self, indent_style: &IndentStyle) -> String {
+        let indent_level = if self.indent >= self.outdent {
+            self.indent - self.outdent
+        } else {
+            log::warn!("Encountered more outdent than indent nodes while calculating indentation: {} outdent, {} indent", self.outdent, self.indent);
+            0
+        };
+        indent_style.as_str().repeat(indent_level)
+    }
+}
 
-    let mut current_line = line;
-    let mut consider_indent = newline;
-    let mut increment_from_line: isize = 0;
+/// An indent definition which corresponds to a capture from the indent query
+struct IndentCapture {
+    capture_type: IndentCaptureType,
+    scope: IndentScope,
+}
+#[derive(Clone, Copy)]
+enum IndentCaptureType {
+    Indent,
+    Outdent,
+}
+impl IndentCaptureType {
+    fn default_scope(&self) -> IndentScope {
+        match self {
+            IndentCaptureType::Indent => IndentScope::Tail,
+            IndentCaptureType::Outdent => IndentScope::All,
+        }
+    }
+}
+/// This defines which part of a node an [IndentCapture] applies to.
+/// Each [IndentCaptureType] has a default scope, but the scope can be changed
+/// with `#set!` property declarations.
+#[derive(Clone, Copy)]
+enum IndentScope {
+    /// The indent applies to the whole node
+    All,
+    /// The indent applies to everything except for the first line of the node
+    Tail,
+}
 
-    loop {
-        let node_kind = node.kind();
-        let start = node.start_position().row;
-        if current_line != start {
-            // Indent/dedent by at most one per line:
-            // .map(|a| {       <-- ({ is two scopes
-            //     let len = 1; <-- indents one level
-            // })               <-- }) is two scopes
-            if consider_indent || increment_from_line < 0 {
-                increment += increment_from_line.signum();
+/// Execute the indent query.
+/// Returns for each node (identified by its id) a list of indent captures for that node.
+fn query_indents(
+    query: &Query,
+    syntax: &Syntax,
+    cursor: &mut QueryCursor,
+    text: RopeSlice,
+    range: std::ops::Range<usize>,
+    // Position of the (optional) newly inserted line break.
+    // Given as (line, byte_pos)
+    new_line_break: Option<(usize, usize)>,
+) -> HashMap<usize, Vec<IndentCapture>> {
+    let mut indent_captures: HashMap<usize, Vec<IndentCapture>> = HashMap::new();
+    cursor.set_byte_range(range);
+    // Iterate over all captures from the query
+    for m in cursor.matches(query, syntax.tree().root_node(), RopeProvider(text)) {
+        // Skip matches where not all custom predicates are fulfilled
+        if !query.general_predicates(m.pattern_index).iter().all(|pred| {
+            match pred.operator.as_ref() {
+                "not-kind-eq?" => match (pred.args.get(0), pred.args.get(1)) {
+                    (
+                        Some(QueryPredicateArg::Capture(capture_idx)),
+                        Some(QueryPredicateArg::String(kind)),
+                    ) => {
+                        let node = m.nodes_for_capture_index(*capture_idx).next();
+                        match node {
+                            Some(node) => node.kind()!=kind.as_ref(),
+                            _ => true,
+                        }
+                    }
+                    _ => {
+                        panic!("Invalid indent query: Arguments to \"not-kind-eq?\" must be a capture and a string");
+                    }
+                },
+                "same-line?" | "not-same-line?" => {
+                    match (pred.args.get(0), pred.args.get(1)) {
+                        (
+                            Some(QueryPredicateArg::Capture(capt1)),
+                            Some(QueryPredicateArg::Capture(capt2))
+                        ) => {
+                            let get_line_num = |node: Node| {
+                                let mut node_line = node.start_position().row;
+                                // Adjust for the new line that will be inserted
+                                if let Some((line, byte)) = new_line_break {
+                                    if node_line==line && node.start_byte()>=byte {
+                                        node_line += 1;
+                                    }
+                                }
+                                node_line
+                            };
+                            let n1 = m.nodes_for_capture_index(*capt1).next();
+                            let n2 = m.nodes_for_capture_index(*capt2).next();
+                            match (n1, n2) {
+                                (Some(n1), Some(n2)) => {
+                                    let same_line = get_line_num(n1)==get_line_num(n2);
+                                    same_line==(pred.operator.as_ref()=="same-line?")
+                                }
+                                _ => true,
+                            }
+                        }
+                        _ => {
+                            panic!("Invalid indent query: Arguments to \"{}\" must be 2 captures", pred.operator);
+                        }
+                    }
+                }
+                _ => {
+                    panic!(
+                        "Invalid indent query: Unknown predicate (\"{}\")",
+                        pred.operator
+                    );
+                }
             }
-            increment_from_line = 0;
-            current_line = start;
-            consider_indent = true;
+        }) {
+            continue;
         }
-
-        if query.outdent.contains(node_kind) {
-            increment_from_line -= 1;
+        for capture in m.captures {
+            let capture_type = query.capture_names()[capture.index as usize].as_str();
+            let capture_type = match capture_type {
+                "indent" => IndentCaptureType::Indent,
+                "outdent" => IndentCaptureType::Outdent,
+                _ => {
+                    // Ignore any unknown captures (these may be needed for predicates such as #match?)
+                    continue;
+                }
+            };
+            let scope = capture_type.default_scope();
+            let mut indent_capture = IndentCapture {
+                capture_type,
+                scope,
+            };
+            // Apply additional settings for this capture
+            for property in query.property_settings(m.pattern_index) {
+                match property.key.as_ref() {
+                    "scope" => {
+                        indent_capture.scope = match property.value.as_deref() {
+                            Some("all") => IndentScope::All,
+                            Some("tail") => IndentScope::Tail,
+                            Some(s) => {
+                                panic!("Invalid indent query: Unknown value for \"scope\" property (\"{}\")", s);
+                            }
+                            None => {
+                                panic!(
+                                    "Invalid indent query: Missing value for \"scope\" property"
+                                );
+                            }
+                        }
+                    }
+                    _ => {
+                        panic!(
+                            "Invalid indent query: Unknown property \"{}\"",
+                            property.key
+                        );
+                    }
+                }
+            }
+            indent_captures
+                .entry(capture.node.id())
+                // Most entries only need to contain a single IndentCapture
+                .or_insert_with(|| Vec::with_capacity(1))
+                .push(indent_capture);
         }
-        if query.indent.contains(node_kind) {
-            increment_from_line += 1;
+    }
+    indent_captures
+}
+
+/// Use the syntax tree to determine the indentation for a given position.
+/// This can be used in 2 ways:
+///
+/// - To get the correct indentation for an existing line (new_line=false), not necessarily equal to the current indentation.
+///   - In this case, pos should be inside the first tree-sitter node on that line.
+///     In most cases, this can just be the first non-whitespace on that line.
+///   - To get the indentation for a new line (new_line=true). This behaves like the first usecase if the part of the current line
+///     after pos were moved to a new line.
+///
+/// The indentation is determined by traversing all the tree-sitter nodes containing the position.
+/// Each of these nodes produces some [AddedIndent] for:
+///
+/// - The line of the (beginning of the) node. This is defined by the scope `all` if this is the first node on its line.
+/// - The line after the node. This is defined by:
+///   - The scope `tail`.
+///   - The scope `all` if this node is not the first node on its line.
+/// Intuitively, `all` applies to everything contained in this node while `tail` applies to everything except for the first line of the node.
+/// The indents from different nodes for the same line are then combined.
+/// The [IndentResult] is simply the sum of the [AddedIndent] for all lines.
+///
+/// Specifying which line exactly an [AddedIndent] applies to is important because indents on the same line combine differently than indents on different lines:
+/// ```ignore
+/// some_function(|| {
+///     // Both the function parameters as well as the contained block should be indented.
+///     // Because they are on the same line, this only yields one indent level
+/// });
+/// ```
+///
+/// ```ignore
+/// some_function(
+///     parm1,
+///     || {
+///         // Here we get 2 indent levels because the 'parameters' and the 'block' node begin on different lines
+///     },
+/// );
+/// ```
+pub fn treesitter_indent_for_pos(
+    query: &Query,
+    syntax: &Syntax,
+    indent_style: &IndentStyle,
+    text: RopeSlice,
+    line: usize,
+    pos: usize,
+    new_line: bool,
+) -> Option<String> {
+    let byte_pos = text.char_to_byte(pos);
+    let mut node = syntax
+        .tree()
+        .root_node()
+        .descendant_for_byte_range(byte_pos, byte_pos)?;
+    let mut first_in_line = get_first_in_line(node, byte_pos, new_line);
+    let new_line_break = if new_line {
+        Some((line, byte_pos))
+    } else {
+        None
+    };
+    let query_result = crate::syntax::PARSER.with(|ts_parser| {
+        let mut ts_parser = ts_parser.borrow_mut();
+        let mut cursor = ts_parser.cursors.pop().unwrap_or_else(QueryCursor::new);
+        let query_result = query_indents(
+            query,
+            syntax,
+            &mut cursor,
+            text,
+            byte_pos..byte_pos + 1,
+            new_line_break,
+        );
+        ts_parser.cursors.push(cursor);
+        query_result
+    });
+
+    let mut result = Indentation::default();
+    // We always keep track of all the indent changes on one line, in order to only indent once
+    // even if there are multiple "indent" nodes on the same line
+    let mut indent_for_line = Indentation::default();
+    let mut indent_for_line_below = Indentation::default();
+    loop {
+        // This can safely be unwrapped because `first_in_line` contains
+        // one entry for each ancestor of the node (which is what we iterate over)
+        let is_first = *first_in_line.last().unwrap();
+        // Apply all indent definitions for this node
+        if let Some(definitions) = query_result.get(&node.id()) {
+            for definition in definitions {
+                match definition.scope {
+                    IndentScope::All => {
+                        if is_first {
+                            indent_for_line.add_capture(definition.capture_type);
+                        } else {
+                            indent_for_line_below.add_capture(definition.capture_type);
+                        }
+                    }
+                    IndentScope::Tail => {
+                        indent_for_line_below.add_capture(definition.capture_type);
+                    }
+                }
+            }
         }
 
         if let Some(parent) = node.parent() {
+            let mut node_line = node.start_position().row;
+            let mut parent_line = parent.start_position().row;
+            if node_line == line && new_line {
+                // Also consider the line that will be inserted
+                if node.start_byte() >= byte_pos {
+                    node_line += 1;
+                }
+                if parent.start_byte() >= byte_pos {
+                    parent_line += 1;
+                }
+            };
+            if node_line != parent_line {
+                if node_line < line + (new_line as usize) {
+                    // Don't add indent for the line below the line of the query
+                    result.add_line(&indent_for_line_below);
+                }
+                if node_line == parent_line + 1 {
+                    indent_for_line_below = indent_for_line;
+                } else {
+                    result.add_line(&indent_for_line);
+                    indent_for_line_below = Indentation::default();
+                }
+                indent_for_line = Indentation::default();
+            }
+
             node = parent;
+            first_in_line.pop();
         } else {
+            result.add_line(&indent_for_line_below);
+            result.add_line(&indent_for_line);
             break;
         }
     }
-    if consider_indent || increment_from_line < 0 {
-        increment += increment_from_line.signum();
-    }
-    increment.max(0) as usize
+    Some(result.as_string(indent_style))
 }
 
-// TODO: two usecases: if we are triggering this for a new, blank line:
-// - it should return 0 when mass indenting stuff
-// - it should look up the wrapper node and count it too when we press o/O
-pub fn suggested_indent_for_pos(
+/// Returns the indentation for a new line.
+/// This is done either using treesitter, or if that's not available by copying the indentation from the current line
+#[allow(clippy::too_many_arguments)]
+pub fn indent_for_newline(
     language_config: Option<&LanguageConfiguration>,
     syntax: Option<&Syntax>,
+    indent_style: &IndentStyle,
+    tab_width: usize,
     text: RopeSlice,
-    pos: usize,
-    line: usize,
-    new_line: bool,
-) -> Option<usize> {
+    line_before: usize,
+    line_before_end_pos: usize,
+    current_line: usize,
+) -> String {
     if let (Some(query), Some(syntax)) = (
         language_config.and_then(|config| config.indent_query()),
         syntax,
     ) {
-        let byte_start = text.char_to_byte(pos);
-        let node = get_highest_syntax_node_at_bytepos(syntax, byte_start);
-        // TODO: special case for comments
-        // TODO: if preserve_leading_whitespace
-        Some(calculate_indentation(query, node, line, new_line))
-    } else {
-        None
+        if let Some(indent) = treesitter_indent_for_pos(
+            query,
+            syntax,
+            indent_style,
+            text,
+            line_before,
+            line_before_end_pos,
+            true,
+        ) {
+            return indent;
+        };
     }
+    let indent_level = indent_level_for_line(text.line(current_line), tab_width);
+    indent_style.as_str().repeat(indent_level)
 }
 
 pub fn get_scopes(syntax: Option<&Syntax>, text: RopeSlice, pos: usize) -> Vec<&'static str> {
@@ -326,156 +632,4 @@ mod test {
         let line = Rope::from("\t    \tfn new"); // 1 tab, 4 spaces, tab
         assert_eq!(indent_level_for_line(line.slice(..), tab_width), 3);
     }
-
-    #[test]
-    fn test_suggested_indent_for_line() {
-        let doc = Rope::from(
-            "
-use std::{
-    io::{self, stdout, Stdout, Write},
-    path::PathBuf,
-    sync::Arc,
-    time::Duration,
-}
-mod test {
-    fn hello_world() {
-        1 + 1;
-
-        let does_indentation_work = 1;
-
-        let test_function = function_with_param(this_param,
-            that_param
-        );
-
-        let test_function = function_with_param(
-            this_param,
-            that_param
-        );
-
-        let test_function = function_with_proper_indent(param1,
-            param2,
-        );
-
-        let selection = Selection::new(
-            changes
-                .clone()
-                .map(|(start, end, text): (usize, usize, Option<Tendril>)| {
-                    let len = text.map(|text| text.len()).unwrap() - 1; // minus newline
-                    let pos = start + len;
-                    Range::new(pos, pos)
-                })
-                .collect(),
-            0,
-        );
-
-        return;
-    }
-}
-
-impl<A, D> MyTrait<A, D> for YourType
-where
-    A: TraitB + TraitC,
-    D: TraitE + TraitF,
-{
-
-}
-#[test]
-//
-match test {
-    Some(a) => 1,
-    None => {
-        unimplemented!()
-    }
-}
-std::panic::set_hook(Box::new(move |info| {
-    hook(info);
-}));
-
-{ { {
-    1
-}}}
-
-pub fn change<I>(document: &Document, changes: I) -> Self
-where
-    I: IntoIterator<Item = Change> + ExactSizeIterator,
-{
-    [
-        1,
-        2,
-        3,
-    ];
-    (
-        1,
-        2
-    );
-    true
-}
-",
-        );
-
-        let doc = doc;
-        use crate::diagnostic::Severity;
-        use crate::syntax::{
-            Configuration, IndentationConfiguration, LanguageConfiguration, Loader,
-        };
-        use once_cell::sync::OnceCell;
-        let loader = Loader::new(Configuration {
-            language: vec![LanguageConfiguration {
-                scope: "source.rust".to_string(),
-                file_types: vec!["rs".to_string()],
-                shebangs: vec![],
-                language_id: "Rust".to_string(),
-                highlight_config: OnceCell::new(),
-                config: None,
-                //
-                injection_regex: None,
-                roots: vec![],
-                comment_token: None,
-                auto_format: false,
-                diagnostic_severity: Severity::Warning,
-                grammar: None,
-                language_server: None,
-                indent: Some(IndentationConfiguration {
-                    tab_width: 4,
-                    unit: String::from("    "),
-                }),
-                indent_query: OnceCell::new(),
-                textobject_query: OnceCell::new(),
-                debugger: None,
-                auto_pairs: None,
-            }],
-        });
-
-        // set runtime path so we can find the queries
-        let mut runtime = std::path::PathBuf::from(env!("CARGO_MANIFEST_DIR"));
-        runtime.push("../runtime");
-        std::env::set_var("HELIX_RUNTIME", runtime.to_str().unwrap());
-
-        let language_config = loader.language_config_for_scope("source.rust").unwrap();
-        let highlight_config = language_config.highlight_config(&[]).unwrap();
-        let syntax = Syntax::new(&doc, highlight_config, std::sync::Arc::new(loader));
-        let text = doc.slice(..);
-        let tab_width = 4;
-
-        for i in 0..doc.len_lines() {
-            let line = text.line(i);
-            if let Some(pos) = crate::find_first_non_whitespace_char(line) {
-                let indent = indent_level_for_line(line, tab_width);
-                assert_eq!(
-                    suggested_indent_for_pos(
-                        Some(&language_config),
-                        Some(&syntax),
-                        text,
-                        text.line_to_char(i) + pos,
-                        i,
-                        false
-                    ),
-                    Some(indent),
-                    "line {}: \"{}\"",
-                    i,
-                    line
-                );
-            }
-        }
-    }
 }
diff --git a/helix-core/src/syntax.rs b/helix-core/src/syntax.rs
index d3750e75..dde7e90c 100644
--- a/helix-core/src/syntax.rs
+++ b/helix-core/src/syntax.rs
@@ -92,7 +92,7 @@ pub struct LanguageConfiguration {
     pub indent: Option<IndentationConfiguration>,
 
     #[serde(skip)]
-    pub(crate) indent_query: OnceCell<Option<IndentQuery>>,
+    pub(crate) indent_query: OnceCell<Option<Query>>,
     #[serde(skip)]
     pub(crate) textobject_query: OnceCell<Option<TextObjectQuery>>,
     #[serde(skip_serializing_if = "Option::is_none")]
@@ -220,17 +220,6 @@ impl FromStr for AutoPairConfig {
     }
 }
 
-#[derive(Debug, Serialize, Deserialize)]
-#[serde(rename_all = "kebab-case")]
-pub struct IndentQuery {
-    #[serde(default)]
-    #[serde(skip_serializing_if = "HashSet::is_empty")]
-    pub indent: HashSet<String>,
-    #[serde(default)]
-    #[serde(skip_serializing_if = "HashSet::is_empty")]
-    pub outdent: HashSet<String>,
-}
-
 #[derive(Debug)]
 pub struct TextObjectQuery {
     pub query: Query,
@@ -404,13 +393,13 @@ impl LanguageConfiguration {
         self.highlight_config.get().is_some()
     }
 
-    pub fn indent_query(&self) -> Option<&IndentQuery> {
+    pub fn indent_query(&self) -> Option<&Query> {
         self.indent_query
             .get_or_init(|| {
-                let language = self.language_id.to_ascii_lowercase();
-
-                let toml = load_runtime_file(&language, "indents.toml").ok()?;
-                toml::from_slice(toml.as_bytes()).ok()
+                let lang_name = self.language_id.to_ascii_lowercase();
+                let query_text = read_query(&lang_name, "indents.scm");
+                let lang = self.highlight_config.get()?.as_ref()?.language;
+                Query::new(lang, &query_text).ok()
             })
             .as_ref()
     }
@@ -557,7 +546,7 @@ impl Loader {
 
 pub struct TsParser {
     parser: tree_sitter::Parser,
-    cursors: Vec<QueryCursor>,
+    pub cursors: Vec<QueryCursor>,
 }
 
 // could also just use a pool, or a single instance?
@@ -1180,7 +1169,7 @@ struct HighlightIter<'a> {
 }
 
 // Adapter to convert rope chunks to bytes
-struct ChunksBytes<'a> {
+pub struct ChunksBytes<'a> {
     chunks: ropey::iter::Chunks<'a>,
 }
 impl<'a> Iterator for ChunksBytes<'a> {
@@ -1190,7 +1179,7 @@ impl<'a> Iterator for ChunksBytes<'a> {
     }
 }
 
-struct RopeProvider<'a>(RopeSlice<'a>);
+pub struct RopeProvider<'a>(pub RopeSlice<'a>);
 impl<'a> TextProvider<'a> for RopeProvider<'a> {
     type I = ChunksBytes<'a>;
 
@@ -2126,7 +2115,7 @@ mod test {
     #[test]
     fn test_load_runtime_file() {
         // Test to make sure we can load some data from the runtime directory.
-        let contents = load_runtime_file("rust", "indents.toml").unwrap();
+        let contents = load_runtime_file("rust", "indents.scm").unwrap();
         assert!(!contents.is_empty());
 
         let results = load_runtime_file("rust", "does-not-exist");
diff --git a/helix-core/tests/data/indent/indent.rs b/helix-core/tests/data/indent/indent.rs
new file mode 120000
index 00000000..2ac16cf9
--- /dev/null
+++ b/helix-core/tests/data/indent/indent.rs
@@ -0,0 +1 @@
+../../../src/indent.rs
\ No newline at end of file
diff --git a/helix-core/tests/data/indent/languages.toml b/helix-core/tests/data/indent/languages.toml
new file mode 100644
index 00000000..f9cef494
--- /dev/null
+++ b/helix-core/tests/data/indent/languages.toml
@@ -0,0 +1,13 @@
+# This languages.toml should contain definitions for all languages for which we have indent tests
+[[language]]
+name = "rust"
+scope = "source.rust"
+injection-regex = "rust"
+file-types = ["rs"]
+comment-token = "//"
+roots = ["Cargo.toml", "Cargo.lock"]
+indent = { tab-width = 4, unit = "    " }
+
+[[grammar]]
+name = "rust"
+source = { git = "https://github.com/tree-sitter/tree-sitter-rust", rev = "a360da0a29a19c281d08295a35ecd0544d2da211" }
diff --git a/helix-core/tests/data/indent/rust.rs b/helix-core/tests/data/indent/rust.rs
new file mode 100644
index 00000000..010745e0
--- /dev/null
+++ b/helix-core/tests/data/indent/rust.rs
@@ -0,0 +1,105 @@
+use std::{
+    io::{self, stdout, Stdout, Write},
+    path::PathBuf,
+    sync::Arc,
+    time::Duration,
+};
+mod test {
+    fn hello_world() {
+        1 + 1;
+
+        let does_indentation_work = 1;
+
+        let mut really_long_variable_name_using_up_the_line =
+            really_long_fn_that_should_definitely_go_on_the_next_line();
+        really_long_variable_name_using_up_the_line =
+            really_long_fn_that_should_definitely_go_on_the_next_line();
+        really_long_variable_name_using_up_the_line |=
+            really_long_fn_that_should_definitely_go_on_the_next_line();
+
+        let (
+            a_long_variable_name_in_this_tuple,
+            b_long_variable_name_in_this_tuple,
+            c_long_variable_name_in_this_tuple,
+            d_long_variable_name_in_this_tuple,
+            e_long_variable_name_in_this_tuple,
+        ): (usize, usize, usize, usize, usize) =
+            if really_long_fn_that_should_definitely_go_on_the_next_line() {
+                (
+                    03294239434,
+                    1213412342314,
+                    21231234134,
+                    834534234549898789,
+                    9879234234543853457,
+                )
+            } else {
+                (0, 1, 2, 3, 4)
+            };
+
+        let test_function = function_with_param(this_param,
+            that_param
+        );
+
+        let test_function = function_with_param(
+            this_param,
+            that_param
+        );
+
+        let test_function = function_with_proper_indent(param1,
+            param2,
+        );
+
+        let selection = Selection::new(
+            changes
+                .clone()
+                .map(|(start, end, text): (usize, usize, Option<Tendril>)| {
+                    let len = text.map(|text| text.len()).unwrap() - 1; // minus newline
+                    let pos = start + len;
+                    Range::new(pos, pos)
+                })
+                .collect(),
+            0,
+        );
+
+        return;
+    }
+}
+
+impl<A, D> MyTrait<A, D> for YourType
+where
+    A: TraitB + TraitC,
+    D: TraitE + TraitF,
+{
+
+}
+#[test]
+//
+match test {
+    Some(a) => 1,
+    None => {
+        unimplemented!()
+    }
+}
+std::panic::set_hook(Box::new(move |info| {
+    hook(info);
+}));
+
+{ { {
+    1
+}}}
+
+pub fn change<I>(document: &Document, changes: I) -> Self
+where
+    I: IntoIterator<Item = Change> + ExactSizeIterator,
+{
+    [
+        1,
+        2,
+        3,
+    ];
+    (
+        1,
+        2
+    );
+    true
+}
diff --git a/helix-core/tests/indent.rs b/helix-core/tests/indent.rs
new file mode 100644
index 00000000..ff04d05f
--- /dev/null
+++ b/helix-core/tests/indent.rs
@@ -0,0 +1,68 @@
+use helix_core::{
+    indent::{treesitter_indent_for_pos, IndentStyle},
+    syntax::Loader,
+    Syntax,
+};
+use std::path::PathBuf;
+
+#[test]
+fn test_treesitter_indent_rust() {
+    test_treesitter_indent("rust.rs", "source.rust");
+}
+#[test]
+fn test_treesitter_indent_rust_2() {
+    test_treesitter_indent("indent.rs", "source.rust");
+    // TODO Use commands.rs as indentation test.
+    // Currently this fails because we can't align the parameters of a closure yet
+    // test_treesitter_indent("commands.rs", "source.rust");
+}
+
+fn test_treesitter_indent(file_name: &str, lang_scope: &str) {
+    let mut test_dir = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
+    test_dir.push("tests/data/indent");
+
+    let mut test_file = test_dir.clone();
+    test_file.push(file_name);
+    let test_file = std::fs::File::open(test_file).unwrap();
+    let doc = ropey::Rope::from_reader(test_file).unwrap();
+
+    let mut config_file = test_dir;
+    config_file.push("languages.toml");
+    let config = std::fs::read(config_file).unwrap();
+    let config = toml::from_slice(&config).unwrap();
+    let loader = Loader::new(config);
+
+    // set runtime path so we can find the queries
+    let mut runtime = std::path::PathBuf::from(env!("CARGO_MANIFEST_DIR"));
+    runtime.push("../runtime");
+    std::env::set_var("HELIX_RUNTIME", runtime.to_str().unwrap());
+
+    let language_config = loader.language_config_for_scope(lang_scope).unwrap();
+    let highlight_config = language_config.highlight_config(&[]).unwrap();
+    let syntax = Syntax::new(&doc, highlight_config, std::sync::Arc::new(loader));
+    let indent_query = language_config.indent_query().unwrap();
+    let text = doc.slice(..);
+
+    for i in 0..doc.len_lines() {
+        let line = text.line(i);
+        if let Some(pos) = helix_core::find_first_non_whitespace_char(line) {
+            let suggested_indent = treesitter_indent_for_pos(
+                indent_query,
+                &syntax,
+                &IndentStyle::Spaces(4),
+                text,
+                i,
+                text.line_to_char(i) + pos,
+                false,
+            )
+            .unwrap();
+            assert!(
+                line.get_slice(..pos).map_or(false, |s| s == suggested_indent),
+                "Wrong indentation on line {}:\n\"{}\" (original line)\n\"{}\" (suggested indentation)\n",
+                i+1,
+                line.slice(..line.len_chars()-1),
+                suggested_indent,
+            );
+        }
+    }
+}