fix(kotlin): classes with newlines (#476)

## What:
This PR makes it so we can parse Kotlin classes that have a newline between the class identifier and constructor.

## Why:
Parse rate.

## How:
The problem is in cases like:
```
class Foo
constructor Bar() { ... }
```

Here, we insert an automatic semicolon between `Foo` and `constructor`. This leaves us able to parse `class Foo` as a `class_declaration`, but `constructor Bar ...` is not allowed on its own.

We simply allow `constructor Bar ...` to be a standalone statement, and resolve to stitch them together at parsing time.

### Testing

Tested with `make test` and `test-lang kotlin`

### Security

- [ ] Change has no security implications (otherwise, ping the security team)

---------

Co-authored-by: Amarin Phaosawasdi <amchiclet@users.noreply.github.com>

lang/semgrep-grammars/src/semgrep-kotlin/grammar.js

@@ -6,7 +6,7 @@
  */
 
 // INVARIATN: Make sure that you are merging any commits into the `semgrep`
-// branch of `tree-sitter-kotlin`! This is because our version of 
+// branch of `tree-sitter-kotlin`! This is because our version of
 // `tree-sitter-kotlin` is forked from the original repository, and we
 // want our branch to be kept separate.
 
@@ -40,7 +40,7 @@ module.exports = grammar(standard_grammar, {
 
         typed_metavar: $ =>  seq(
           "(", $.simple_identifier, ":", $._type, ")"
-        ), 
+        ),
 
         // Statement ellipsis: '...' not followed by ';'
         _expression: ($, previous) => {
@@ -74,13 +74,48 @@ module.exports = grammar(standard_grammar, {
 	    );
 	},
 
+  // We would like to be able to parse programs which have a newline between the
+  // class name and the constructor:
+  // class Foo
+  // constructor Bar() { ... }
+
+  // The problem is that the Kotlin parser inserts a semicolon after "Foo", making
+  // it such that we get interrupted in the middle of the class_declaration.
+  // To make it so we can continue, we allow everything after the class identifier
+  // to be a standalone statement in its own right. This way, we can parse both parts
+  // individually, and stitch them together at parsing time.
+
+  // We only need to amend statements here, because the consumers of _declaration are
+  // only class_member_declaration, top_level_object and _statement.
+  // The former has `secondary_constructor`, which already looks like what we want to
+  // add, and the second seems to be unused.
+  // So we just need to fix _statement.
+
+  // A more proper fix would likely require changes to the external scanner to properly
+  // handle automatic semicolon insertion, which is the cause of this whole issue.
+  // We filed an issue to tree-sitter-kotlin to track this:
+  // https://github.com/fwcd/tree-sitter-kotlin/issues/75
+  _statement: ($, previous) => choice(
+    ...previous.members,
+    $.partial_class_declaration,
+  ),
+
+  partial_class_declaration: $ => prec.left(seq(
+    optional($.type_parameters),
+    seq(optional($.modifiers), "constructor"),
+    $._class_parameters,
+    optional(seq(":", $._delegation_specifiers)),
+    optional($.type_constraints),
+    optional($.class_body)
+  )),
+
 	class_parameter: ($, previous) => {
 	    return choice(
 		previous,
 		$.ellipsis
 	    );
 	},
-	
+
         deep_ellipsis: $ => seq(
             '<...', $._expression, '...>'
         ),

lang/semgrep-grammars/src/semgrep-kotlin/test/corpus/semgrep.txt

@@ -32,7 +32,6 @@ class $CLASS {
                   (value_argument
                     (integer_literal)))))))))))
 
-
 =====================================
 Typed Metavariables
 =====================================
@@ -54,7 +53,7 @@ val x = ($X : int)
 Ellipsis Metavariable
 =====================================
 
-$...X 
+$...X
 val x = 2
 
 ---
@@ -67,7 +66,7 @@ val x = 2
     (integer_literal)))
 
 =====================================
-Expression Ellipsis 
+Expression Ellipsis
 =====================================
 
 class Foo {
@@ -89,7 +88,6 @@ class Foo {
           (statements
             (ellipsis)))))))
 
-
 =====================================
 Deep Ellipsis
 =====================================
@@ -132,22 +130,31 @@ class Foo {
 }
 
 ---
+
 (source_file
-    (class_declaration (type_identifier)
-       (class_body (ellipsis))))
+  (class_declaration
+    (type_identifier)
+    (class_body
+      (ellipsis))))
 
 =====================================
 Argument Ellipsis
 =====================================
 foo(1, ..., 2)
 
 ---
+
 (source_file
-   (call_expression (simple_identifier)
-      (call_suffix (value_arguments
-         (value_argument (integer_literal))
-	 (value_argument (ellipsis))
-	 (value_argument (integer_literal))))))
+  (call_expression
+    (simple_identifier)
+    (call_suffix
+      (value_arguments
+        (value_argument
+          (integer_literal))
+        (value_argument
+          (ellipsis))
+        (value_argument
+          (integer_literal))))))
 
 =====================================
 Parameter Ellipsis
@@ -157,12 +164,16 @@ fun foo(..., bar: String, ...) {}
 ---
 
 (source_file
-  (function_declaration (simple_identifier)
-     (function_value_parameters
+  (function_declaration
+    (simple_identifier)
+    (function_value_parameters
       (ellipsis)
-      (parameter (simple_identifier) (user_type (type_identifier)))
+      (parameter
+        (simple_identifier)
+        (user_type
+          (type_identifier)))
       (ellipsis))
-     (function_body))) 
+    (function_body)))
 
 =====================================
 Class Parameter Ellipsis
@@ -171,11 +182,17 @@ class Foo(...) : Filter {
 }
 
 ---
+
 (source_file
-   (class_declaration (type_identifier)
-       (primary_constructor (class_parameter (ellipsis)))
-       (delegation_specifier (user_type (type_identifier)))
-     (class_body)))
+  (class_declaration
+    (type_identifier)
+    (primary_constructor
+      (class_parameter
+        (ellipsis)))
+    (delegation_specifier
+      (user_type
+        (type_identifier)))
+    (class_body)))
 
 =====================================
 Statement Ellipsis
@@ -187,15 +204,22 @@ fun foo() {
 }
 
 ---
+
 (source_file
-  (function_declaration (simple_identifier)
+  (function_declaration
+    (simple_identifier)
     (function_value_parameters)
     (function_body
       (statements
-        (call_expression (simple_identifier) (call_suffix (value_arguments)))
-	(ellipsis)
-	(call_expression (simple_identifier) (call_suffix (value_arguments))))
-	)))
+        (call_expression
+          (simple_identifier)
+          (call_suffix
+            (value_arguments)))
+        (ellipsis)
+        (call_expression
+          (simple_identifier)
+          (call_suffix
+            (value_arguments)))))))
 
 =====================================
 Statement Ellipsis and metavarible
@@ -205,11 +229,17 @@ $COOKIE.setValue("")
 ...
 
 ---
+
 (source_file
   (call_expression
-    (navigation_expression (simple_identifier)
-       (navigation_suffix (simple_identifier)))
-    (call_suffix (value_arguments (value_argument (string_literal)))))
+    (navigation_expression
+      (simple_identifier)
+      (navigation_suffix
+        (simple_identifier)))
+    (call_suffix
+      (value_arguments
+        (value_argument
+          (string_literal)))))
   (ellipsis))
 
 =====================================
@@ -218,14 +248,97 @@ Method chaining Ellipsis
 obj. ... .foo().bar()
 
 ---
+
 (source_file
   (call_expression
     (navigation_expression
       (call_expression
         (navigation_expression
-	   (navigation_expression (simple_identifier)
-	     (navigation_suffix (ellipsis)))
-	   (navigation_suffix (simple_identifier)))
-	(call_suffix (value_arguments)))
-      (navigation_suffix (simple_identifier)))
-    (call_suffix (value_arguments))))
+          (navigation_expression
+            (simple_identifier)
+            (navigation_suffix
+              (ellipsis)))
+          (navigation_suffix
+            (simple_identifier)))
+        (call_suffix
+          (value_arguments)))
+      (navigation_suffix
+        (simple_identifier)))
+    (call_suffix
+      (value_arguments))))
+
+=====================================
+Class with a newline
+=====================================
+
+class BlahClass
+constructor(arg: Int) {
+  private val blah2 = "foo${arg}"
+}
+
+---
+
+(source_file
+  (class_declaration
+    (type_identifier))
+  (partial_class_declaration
+    (class_parameter
+      (simple_identifier)
+      (user_type
+        (type_identifier)))
+    (class_body
+      (property_declaration
+        (modifiers
+          (visibility_modifier))
+        (variable_declaration
+          (simple_identifier))
+        (string_literal
+          (interpolated_expression
+            (simple_identifier)))))))
+
+=====================================
+Class in a class
+=====================================
+
+class Foo {
+  class BlahClass
+  constructor(arg: Int) {
+    private val blah2 = "foo${arg}"
+  }
+}
+
+---
+
+(source_file
+  (class_declaration
+    (type_identifier)
+    (class_body
+      (class_declaration
+        (type_identifier))
+      (secondary_constructor
+        (function_value_parameters
+          (parameter
+            (simple_identifier)
+            (user_type
+              (type_identifier))))
+        (statements
+          (property_declaration
+            (modifiers
+              (visibility_modifier))
+            (variable_declaration
+              (simple_identifier))
+            (string_literal
+              (interpolated_expression
+                (simple_identifier)))))))))
+
+=====================================
+Class without body
+=====================================
+
+class Foo
+
+---
+
+(source_file
+  (class_declaration
+    (type_identifier)))