better recovery for syntax errors in parameter list (PY-3635); fix old bug with tuple parameters parsing

python/src/com/jetbrains/python/parsing/FunctionParsing.java

@@ -113,16 +113,17 @@ public class FunctionParsing extends Parsing {
         if (myBuilder.getTokenType() == PyTokenTypes.COMMA) {
           myBuilder.advanceLexer();
         }
-        else if (myBuilder.getTokenType() == PyTokenTypes.LPAR) {
-          parseParameterSubList();
-          continue;
-        }
         else {
           myBuilder.error(message("PARSE.expected.comma.lpar.rpar"));
           break;
         }
       }
 
+      if (myBuilder.getTokenType() == PyTokenTypes.LPAR) {
+        parseParameterSubList();
+        continue;
+      }
+
       final PsiBuilder.Marker parameter = myBuilder.mark();
       boolean isStarParameter = false;
       if (myBuilder.getTokenType() == PyTokenTypes.MULT) {
@@ -155,8 +156,13 @@ public class FunctionParsing extends Parsing {
         parameter.done(PyElementTypes.NAMED_PARAMETER);
       }
       else {
-        myBuilder.error(message("PARSE.expected.formal.param.name"));
         parameter.rollbackTo();
+        PsiBuilder.Marker invalidElements = myBuilder.mark();
+        while (!atToken(endToken) && !atToken(PyTokenTypes.LINE_BREAK) && !atToken(PyTokenTypes.COMMA) && !atToken(null)) {
+          nextToken();
+        }
+        invalidElements.error(message("PARSE.expected.formal.param.name"));
+        break;
       }
     }
 

python/src/com/jetbrains/python/parsing/Parsing.java

@@ -5,6 +5,7 @@ import com.intellij.openapi.diagnostic.Logger;
 import com.intellij.psi.tree.IElementType;
 import com.intellij.psi.tree.TokenSet;
 import com.jetbrains.python.psi.PyElementType;
+import org.jetbrains.annotations.Nullable;
 
 /**
  * @author yole
@@ -57,7 +58,7 @@ public class Parsing {
     LOG.assertTrue(myBuilder.getTokenType() == tokenType);
   }
 
-  protected boolean atToken(final IElementType tokenType) {
+  protected boolean atToken(@Nullable final IElementType tokenType) {
     return myBuilder.getTokenType() == tokenType;
   }
 

python/testData/psi/ErrorInParameterList.py

@@ -0,0 +1,2 @@
+def select2 (self,filds=None, from=''):
+        print (sql)

python/testData/psi/ErrorInParameterList.txt

@@ -0,0 +1,34 @@
+PyFile:ErrorInParameterList.py
+  PyFunction('select2')
+    PsiElement(Py:DEF_KEYWORD)('def')
+    PsiWhiteSpace(' ')
+    PsiElement(Py:IDENTIFIER)('select2')
+    PsiWhiteSpace(' ')
+    PyParameterList
+      PsiElement(Py:LPAR)('(')
+      PyNamedParameter('self')
+        PsiElement(Py:IDENTIFIER)('self')
+      PsiElement(Py:COMMA)(',')
+      PyNamedParameter('filds')
+        PsiElement(Py:IDENTIFIER)('filds')
+        PsiElement(Py:EQ)('=')
+        PyReferenceExpression: None
+          PsiElement(Py:IDENTIFIER)('None')
+      PsiElement(Py:COMMA)(',')
+      PsiWhiteSpace(' ')
+      PsiErrorElement:formal parameter name expected
+        PsiElement(Py:FROM_KEYWORD)('from')
+        PsiElement(Py:EQ)('=')
+        PsiElement(Py:STRING_LITERAL)('''')
+      PsiElement(Py:RPAR)(')')
+    PsiElement(Py:COLON)(':')
+    PsiWhiteSpace('\n        ')
+    PyStatementList
+      PyPrintStatement
+        PsiElement(Py:PRINT_KEYWORD)('print')
+        PsiWhiteSpace(' ')
+        PyParenthesizedExpression
+          PsiElement(Py:LPAR)('(')
+          PyReferenceExpression: sql
+            PsiElement(Py:IDENTIFIER)('sql')
+          PsiElement(Py:RPAR)(')')

python/testSrc/com/jetbrains/python/PythonParsingTest.java

@@ -267,6 +267,10 @@ public class PythonParsingTest extends ParsingTestCase {
     doTest();
   }
 
+  public void testErrorInParameterList() {  // PY-3635
+    doTest();
+  }
+
   public void doTest() {
     doTest(LanguageLevel.PYTHON25);
   }