From ac5f5705e030d385f2adc972323054b90bae68d2 Mon Sep 17 00:00:00 2001
From: Mikhail Golubev <mikhail.golubev@jetbrains.com>
Date: Wed, 22 Oct 2025 22:37:11 +0300
Subject: [PATCH] [python] refactoring: Introduce
 PyAstNamedParameter.isPositionalOnly

GitOrigin-RevId: f072b2135128fdfb1d46dca68232968b20a6b078
---
 .../python/ast/PyAstNamedParameter.java       | 43 +++++++++++++++
 .../PyMiscellaneousPsiOperationsTest.java     | 53 +++++++++++++++++++
 2 files changed, 96 insertions(+)

diff --git a/python/python-ast/src/com/jetbrains/python/ast/PyAstNamedParameter.java b/python/python-ast/src/com/jetbrains/python/ast/PyAstNamedParameter.java
index f7c6b64a9633..57da256a4127 100644
--- a/python/python-ast/src/com/jetbrains/python/ast/PyAstNamedParameter.java
+++ b/python/python-ast/src/com/jetbrains/python/ast/PyAstNamedParameter.java
@@ -18,6 +18,7 @@ package com.jetbrains.python.ast;
 import com.intellij.lang.ASTNode;
 import com.intellij.psi.*;
 import com.intellij.util.ObjectUtils;
+import com.jetbrains.python.PyNamesKt;
 import com.jetbrains.python.PyTokenTypes;
 import com.jetbrains.python.PythonDialectsTokenSetProvider;
 import com.jetbrains.python.ast.impl.ParamHelperCore;
@@ -136,6 +137,48 @@ public interface PyAstNamedParameter extends PyAstParameter, PsiNamedElement, Ps
     return varargSeen;
   }
 
+  default boolean isPositionalOnly() {
+    if (isSelf() ||
+        isKeywordContainer() ||
+        isPositionalContainer() ||
+        this instanceof PyAstSingleStarParameter ||
+        this instanceof PyAstSlashParameter) {
+      return false;
+    }
+    final PyAstParameterList parameters = getStubOrPsiParentOfType(PyAstParameterList.class);
+    if (parameters == null) {
+      return false;
+    }
+    boolean thisSeen = false;
+    boolean allBeforeThisPrivate = true;
+    for (PyAstParameter param : parameters.getParameters()) {
+      if (param.isSelf()) {
+        continue;
+      }
+      if (param instanceof PyAstSingleStarParameter ||
+          (param instanceof PyAstNamedParameter np && (np.isPositionalContainer() || np.isKeywordContainer()))) {
+        // None of the positional-only parameter kinds can follow these
+        if (!thisSeen) {
+          return false;
+        }
+        // No need to continue, as `/` can't follow them either
+        break;
+      }
+      // New-style positional-only syntax, decide purely by the position
+      if (param instanceof PyAstSlashParameter) {
+        return thisSeen;
+      }
+      if (param == this) {
+        thisSeen = true;
+      }
+      else if (!thisSeen) {
+        allBeforeThisPrivate &= param.getName() != null && PyNamesKt.isPrivate(param.getName());
+      }
+    }
+    // Legacy-style positional only
+    return thisSeen && allBeforeThisPrivate && getName() != null && PyNamesKt.isPrivate(getName());
+  }
+
   @Override
   default boolean isSelf() {
     if (isPositionalContainer() || isKeywordContainer()) {
diff --git a/python/testSrc/com/jetbrains/python/PyMiscellaneousPsiOperationsTest.java b/python/testSrc/com/jetbrains/python/PyMiscellaneousPsiOperationsTest.java
index 2fd99640ae6b..f122e18428db 100644
--- a/python/testSrc/com/jetbrains/python/PyMiscellaneousPsiOperationsTest.java
+++ b/python/testSrc/com/jetbrains/python/PyMiscellaneousPsiOperationsTest.java
@@ -152,4 +152,57 @@ public class PyMiscellaneousPsiOperationsTest extends PyTestCase {
     final PyQualifiedExpression expr = (PyQualifiedExpression)generator.createExpressionFromText(LanguageLevel.PYTHON27, expression);
     assertEquals(expectedQualifiedName, expr.asQualifiedName());
   }
+
+  public void testNamedParameterIsPositionalOnly() {
+    doTestParameterIsPositionalOnly(List.of(false, true, true, false, false), """
+      class C:
+          def func(__self, __a, __b, c, __d):
+              pass
+      """);
+    doTestParameterIsPositionalOnly(List.of(true, true), """
+      class C:
+          @staticmethod
+          def func(__self, __a):
+              pass
+      """);
+    doTestParameterIsPositionalOnly(List.of(false, true), """
+      class C:
+          @classmethod
+          def func(__self, __a):
+              pass
+      """);
+    doTestParameterIsPositionalOnly(List.of(true, true), """
+      def func(__self, __a):
+          pass
+      """);
+    doTestParameterIsPositionalOnly(List.of(false, true, false, false), """
+      class C:
+          def func(self, __a, *__args, __b):
+              pass
+      """);
+    doTestParameterIsPositionalOnly(List.of(false, true, false, false), """
+      class C:
+          def func(self, __a, *, __b):
+              pass
+      """);
+    doTestParameterIsPositionalOnly(List.of(false, true, false), """
+      class C:
+          def func(self, __a, **__kwargs):
+              pass
+      """);
+    doTestParameterIsPositionalOnly(List.of(false, true, false, false), """
+      class C:
+          def func(self, a, /, __b):
+              pass
+      """);
+  }
+
+  private void doTestParameterIsPositionalOnly(List<Boolean> expected, String testData) {
+    myFixture.configureByText("a.py", testData);
+    PyFunction func = myFixture.findElementByText("func", PyFunction.class);
+    assertNotNull(func);
+    List<Boolean> actual = ContainerUtil.map(func.getParameterList().getParameters(),
+                                             p -> p instanceof PyNamedParameter np && np.isPositionalOnly());
+    assertOrderedEquals(actual, expected);
+  }
 }