feat: Indent backslash continuation lines according to style guide (#218)

Close #180

* Indent backslash continuation lines according to style guide

From gdscript style guide[^1]:
> Use 2 indent levels to distinguish continuation lines from regular code blocks.

Currently the formatter indents continuation lines to the same level as
the first line:

```gdscript
func test(thing):
    thing.calling(1) \
    .a(12314) \
    .long() \
    .chain("a string breaks things") \
    .of() \
    .functions()
```

With this change, continuation lines (joined with a backslash) are
formatted with double indention:

```gdscript
func test(thing):
    thing.calling(1) \
            .a(12314) \
            .long() \
            .chain("a string breaks things") \
            .of() \
            .functions()
```

fixes #180

[^1]: https://docs.godotengine.org/en/stable/tutorials/scripting/gdscript/gdscript_styleguide.html#indentation

* Use queries to narrow and address the indent backslash continuation line issue

---------

Co-authored-by: Nathan Lovato <12694995+NathanLovato@users.noreply.github.com>

Author: dmlary

queries/gdscript.scm

@@ -246,3 +246,10 @@
 (get_node) @leaf
 
 (line_continuation) @prepend_space @append_antispace @append_hardline
+; Indent nodes that immediately follows a line continuation ("\") by two levels,
+; following the GDScript style guide. The line_continuation token only appears
+; as a direct child of these three node types. We're leaving arrays, dicts, and
+; enums out because they should have a single indent level inside their bodies
+(attribute (line_continuation) @append_indent_start @append_indent_start . (_) @append_indent_end @append_indent_end)
+(binary_operator (line_continuation) @append_indent_start @append_indent_start . (_) @append_indent_end @append_indent_end)
+(variable_statement (line_continuation) @append_indent_start @append_indent_start . (_) @append_indent_end @append_indent_end)

src/formatter.rs

@@ -53,6 +53,7 @@ struct Formatter {
     input_tree: GdTree,
     tree: Tree,
     original_source: Option<String>,
+    indent_string: String,
 }
 
 impl Formatter {
@@ -72,6 +73,11 @@ impl Formatter {
         } else {
             None
         };
+        let indent_string = if config.use_spaces {
+            " ".repeat(config.indent_size)
+        } else {
+            "\t".to_string()
+        };
 
         Self {
             original_source,
@@ -80,22 +86,17 @@ impl Formatter {
             tree,
             input_tree,
             parser,
+            indent_string,
         }
     }
 
     #[inline(always)]
     fn format(&mut self) -> Result<&mut Self, Box<dyn std::error::Error>> {
-        let indent_string = if self.config.use_spaces {
-            " ".repeat(self.config.indent_size)
-        } else {
-            "\t".to_string()
-        };
-
         let language = Language {
             name: "gdscript".to_owned(),
             query: TopiaryQuery::new(&tree_sitter_gdscript::LANGUAGE.into(), QUERY).unwrap(),
             grammar: tree_sitter_gdscript::LANGUAGE.into(),
-            indent: Some(indent_string),
+            indent: Some(self.indent_string.clone()),
         };
 
         let mut output = Vec::new();
@@ -528,7 +529,9 @@ impl Formatter {
                 .root_node()
                 .descendant_for_byte_range(start_byte, start_byte)
                 .unwrap();
-            if node.kind() == "string" {
+            // String nodes may also contain escape_sequence nodes.  These are
+            // found when a backslash is present within a string.
+            if node.kind() == "string" || node.kind() == "escape_sequence" {
                 continue;
             }
 

tests/expected/line_continuation.gd

@@ -1,4 +1,4 @@
 func _handles(resource: Resource) -> bool:
 	return resource is NoiseTexture2D \
-	or resource is GradientTexture1D \
-	or resource is GradientTexture2D
+			or resource is GradientTexture1D \
+			or resource is GradientTexture2D

tests/expected/line_continuation_indent.gd

@@ -0,0 +1,31 @@
+var is_valid: bool = some_condition \
+		and another_condition
+
+
+func _handles(resource: Resource) -> bool:
+	return resource is NoiseTexture2D \
+			or resource is GradientTexture1D
+
+
+func _process(delta: float) -> void:
+	if is_on_floor() \
+			and not is_jumping:
+		apply_gravity(delta)
+
+
+func _calculate() -> float:
+	var x: float = some_long_value \
+			+ another_value
+	return x
+
+
+func _ready() -> void:
+	node.set_position(Vector2.ZERO) \
+			.rotated(PI)
+
+
+# string with \ must not change indentation
+func _get_message() -> String:
+	var greeting: String = "\
+	Hello world"
+	return greeting

tests/input/line_continuation_indent.gd

@@ -0,0 +1,31 @@
+var is_valid: bool = some_condition \
+and another_condition
+
+
+func _handles(resource: Resource) -> bool:
+	return resource is NoiseTexture2D \
+	or resource is GradientTexture1D
+
+
+func _process(delta: float) -> void:
+	if is_on_floor() \
+	and not is_jumping:
+		apply_gravity(delta)
+
+
+func _calculate() -> float:
+	var x: float = some_long_value \
+	+ another_value
+	return x
+
+
+func _ready() -> void:
+	node.set_position(Vector2.ZERO) \
+	.rotated(PI)
+
+
+# string with \ must not change indentation
+func _get_message() -> String:
+	var greeting: String = "\
+	Hello world"
+	return greeting