QmlJs: Fix reformatter for arrow functions

Fixes: QTCREATORBUG-23019
Change-Id: I6c6bee7092cb12f225ad744df2b3834dfd4bbc8f
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@qt.io>

src/libs/qmljs/parser/qmljs.g

@@ -4019,14 +4019,16 @@ ArrowFunction_In: ArrowParameters T_ARROW ConciseBodyLookahead AssignmentExpress
 /.
     case $rule_number: {
         AST::ReturnStatement *ret = new (pool) AST::ReturnStatement(sym(4).Expression);
-        ret->returnToken = sym(4).Node->firstSourceLocation();
+        const auto zeroLength = [](SourceLocation l){ l.length = 0; return l; };
-        ret->semicolonToken = sym(4).Node->lastSourceLocation();
+        ret->returnToken = zeroLength(sym(4).Node->firstSourceLocation());
+        ret->semicolonToken = zeroLength(sym(4).Node->lastSourceLocation());
         AST::StatementList *statements = (new (pool) AST::StatementList(ret))->finish();
-        AST::FunctionExpression *f = new (pool) AST::FunctionExpression(QStringView(), sym(1).FormalParameterList, statements);
+        AST::FunctionExpression *f = new (pool)
+            AST::FunctionExpression(QStringView(), sym(1).FormalParameterList, statements);
         f->isArrowFunction = true;
         f->functionToken = sym(1).Node ? sym(1).Node->firstSourceLocation() : loc(1);
-        f->lbraceToken = sym(4).Node->firstSourceLocation();
+        f->lbraceToken = zeroLength(sym(4).Node->firstSourceLocation());
-        f->rbraceToken = sym(4).Node->lastSourceLocation();
+        f->rbraceToken = zeroLength(sym(4).Node->lastSourceLocation());
         sym(1).Node = f;
     } break;
 ./
@@ -4039,7 +4041,7 @@ ArrowFunction_In: ArrowParameters T_ARROW ConciseBodyLookahead T_FORCE_BLOCK Fun
         AST::FunctionExpression *f = new (pool) AST::FunctionExpression(QStringView(), sym(1).FormalParameterList, sym(6).StatementList);
         f->isArrowFunction = true;
         f->functionToken = sym(1).Node ? sym(1).Node->firstSourceLocation() : loc(1);
-        f->lbraceToken = loc(6);
+        f->lbraceToken = loc(5);
         f->rbraceToken = loc(7);
         sym(1).Node = f;
     } break;

src/libs/qmljs/parser/qmljsparser.cpp

@@ -3001,15 +3001,16 @@ case 241: {
 
     case 528: {
         AST::ReturnStatement *ret = new (pool) AST::ReturnStatement(sym(4).Expression);
-        ret->returnToken = sym(4).Node->firstSourceLocation();
+        const auto zeroLength = [](SourceLocation l){ l.length = 0; return l; };
-        ret->semicolonToken = sym(4).Node->lastSourceLocation();
+        ret->returnToken = zeroLength(sym(4).Node->firstSourceLocation());
+        ret->semicolonToken = zeroLength(sym(4).Node->lastSourceLocation());
         AST::StatementList *statements = (new (pool) AST::StatementList(ret))->finish();
         AST::FunctionExpression *f = new (pool)
             AST::FunctionExpression(QStringView(), sym(1).FormalParameterList, statements);
         f->isArrowFunction = true;
         f->functionToken = sym(1).Node ? sym(1).Node->firstSourceLocation() : loc(1);
-        f->lbraceToken = sym(4).Node->firstSourceLocation();
+        f->lbraceToken = zeroLength(sym(4).Node->firstSourceLocation());
-        f->rbraceToken = sym(4).Node->lastSourceLocation();
+        f->rbraceToken = zeroLength(sym(4).Node->lastSourceLocation());
         sym(1).Node = f;
     } break;
 
@@ -3022,7 +3023,7 @@ case 241: {
             AST::FunctionExpression(QStringView(), sym(1).FormalParameterList, sym(6).StatementList);
         f->isArrowFunction = true;
         f->functionToken = sym(1).Node ? sym(1).Node->firstSourceLocation() : loc(1);
-        f->lbraceToken = loc(6);
+        f->lbraceToken = loc(5);
         f->rbraceToken = loc(7);
         sym(1).Node = f;
     } break;

src/libs/qmljs/qmljsreformatter.cpp

@@ -1097,7 +1097,8 @@ protected:
     {
         out(ast->returnToken);
         if (ast->expression) {
-            out(" ");
+            if (ast->returnToken.isValid())
+                out(" ");
             accept(ast->expression);
         }
         return false;
@@ -1218,17 +1219,32 @@ protected:
 
     bool visit(FunctionExpression *ast) override
     {
-        out("function ", ast->functionToken);
+        if (!ast->isArrowFunction) {
-        if (!ast->name.isNull())
+            out("function ", ast->functionToken);
-            out(ast->identifierToken);
+            if (!ast->name.isNull())
+                out(ast->identifierToken);
+        }
         out(ast->lparenToken);
+        if (ast->isArrowFunction && ast->formals && ast->formals->next)
+            out("(");
         accept(ast->formals);
+        if (ast->isArrowFunction && ast->formals && ast->formals->next)
+            out(")");
         out(ast->rparenToken);
+        if (ast->isArrowFunction && !ast->formals)
+            out("()");
         out(" ");
+        if (ast->isArrowFunction)
+            out("=> ");
         out(ast->lbraceToken);
         if (ast->body) {
-            lnAcceptIndented(ast->body);
+            if (ast->body->next || ast->lbraceToken.isValid()) {
-            newLine();
+                lnAcceptIndented(ast->body);
+                newLine();
+            } else {
+                // print a single statement in one line. E.g. x => x * 2
+                accept(ast->body);
+            }
         }
         out(ast->rbraceToken);
         return false;

tests/auto/qml/reformatter/jssyntax.js

@@ -12,6 +12,15 @@ function foo(a, b) {
 
 var foo = function (a, b) {}
 
+const func1 = x => x * 2
+const func2 = x => {
+    return x * 7
+}
+const func3 = (x, y) => x + y
+const func4 = (x, y) => {
+    return x + y
+}
+
 while (true) {
     for (var a = 1; a < 5; ++a) {
         switch (a) {