Implement parsing of desctructuring declarations in lambdas

#KT-5828 In Progress

compiler/frontend/src/org/jetbrains/kotlin/parsing/KotlinExpressionParsing.java

@@ -45,6 +45,7 @@ public class KotlinExpressionParsing extends AbstractKotlinParsing {
 
     private static final IElementType[] LOCAL_DECLARATION_FIRST =
             new IElementType[] {CLASS_KEYWORD, INTERFACE_KEYWORD, FUN_KEYWORD, VAL_KEYWORD, VAR_KEYWORD, TYPE_ALIAS_KEYWORD};
+    private static final TokenSet TOKEN_SET_TO_FOLLOW_AFTER_DESTRUCTURING_DECLARATION_IN_LAMBDA = TokenSet.create(ARROW, COMMA, COLON);
 
     private static ImmutableMap<String, KtToken> tokenSetToMap(TokenSet tokens) {
         ImmutableMap.Builder<String, KtToken> builder = ImmutableMap.builder();
@@ -1054,10 +1055,11 @@ public class KotlinExpressionParsing extends AbstractKotlinParsing {
             advance(); // ARROW
             paramsFound = true;
         }
-        else if (at(IDENTIFIER) || at(COLON)) {
+        else if (at(IDENTIFIER) || at(COLON) || at(LPAR)) {
             // Try to parse a simple name list followed by an ARROW
             //   {a -> ...}
             //   {a, b -> ...}
+            //   {(a, b) -> ... }
             PsiBuilder.Marker rollbackMarker = mark();
             IElementType nextToken = lookahead(1);
             boolean preferParamsToExpressions = (nextToken == COMMA || nextToken == COLON);
@@ -1144,7 +1146,11 @@ public class KotlinExpressionParsing extends AbstractKotlinParsing {
 
 
     /*
-     * (SimpleName (":" type)?){","}
+     * lambdaParameter{","}
+     *
+     * lambdaParameter
+     *   : variableDeclarationEntry
+     *   : multipleVariableDeclarations (":" type)?
      */
     private void parseFunctionLiteralParameterList() {
         PsiBuilder.Marker parameterList = mark();
@@ -1155,6 +1161,11 @@ public class KotlinExpressionParsing extends AbstractKotlinParsing {
             if (at(COLON)) {
                 error("Expecting parameter name");
             }
+            else if (at(LPAR)) {
+                PsiBuilder.Marker destructuringDeclaration = mark();
+                myKotlinParsing.parseMultiDeclarationName(TOKEN_SET_TO_FOLLOW_AFTER_DESTRUCTURING_DECLARATION_IN_LAMBDA);
+                destructuringDeclaration.done(DESTRUCTURING_DECLARATION);
+            }
             else {
                 expect(IDENTIFIER, "Expecting parameter name", TokenSet.create(ARROW));
             }

compiler/frontend/src/org/jetbrains/kotlin/parsing/KotlinParsing.java

@@ -1325,7 +1325,7 @@ public class KotlinParsing extends AbstractKotlinParsing {
     }
 
     /*
-     * (SimpleName (":" type)){","}
+     * (SimpleName (":" type){","})
      */
     public void parseMultiDeclarationName(TokenSet follow) {
         // Parsing multi-name, e.g.