CPP-51572 [debugger]: fix debug switcher showing in non-python sessions

The problem was noticed in CLion, where mode switcher is shown even if a cpp file is being debugged. The reason of the problem is that we decided to show the switcher even if no handlers are registered (Python DAP/Jupyter are not installed) for promotion purposes.

The fix is to move part of condition (show switcher only during Python debug sessions) from handlers to switcher directly

Merge-request: IJ-MR-217766
Merged-by: Maxim Popov <maxim.popov@jetbrains.com>

(cherry picked from commit 00cedac5434715f87e131d6bfd99ec9ccb18155d)


Merge-request: IJ-MR-217937
Merged-by: Maxim Popov <maxim.popov@jetbrains.com>

GitOrigin-RevId: b2cbda67623ca368400eeeb7b7313a92d567b448

python/src/com/jetbrains/python/debugger/PyDebuggerBackendSwitchHandler.kt

@@ -25,6 +25,8 @@ interface PyDebuggerBackendSwitchHandler {
   /**
    * Controls visibility of the backend switcher UI.
    * Return false to hide the switcher (e.g., when the currently open file uses a remote kernel).
+   * This is one of two gates: returning true does not show the switcher by itself, since it is also
+   * hidden on Debug tool window tabs that do not run a Python or Jupyter session.
    */
   fun shouldShowSwitcher(project: Project): Boolean = true
 

python/src/com/jetbrains/python/debugger/PyDebuggerBackendSwitcherAction.kt

@@ -13,6 +13,7 @@ import com.intellij.openapi.actionSystem.AnAction
 import com.intellij.openapi.actionSystem.AnActionEvent
 import com.intellij.openapi.actionSystem.DataContext
 import com.intellij.openapi.actionSystem.DefaultActionGroup
+import com.intellij.openapi.actionSystem.LangDataKeys
 import com.intellij.openapi.actionSystem.ex.ActionUtil
 import com.intellij.openapi.actionSystem.ex.ComboBoxAction
 import com.intellij.openapi.components.service
@@ -47,9 +48,11 @@ import com.intellij.util.ui.JBUI
 import com.jetbrains.python.sdk.findPythonSdk
 import kotlinx.coroutines.launch
 import com.intellij.openapi.projectRoots.Sdk
+import com.intellij.platform.debugger.impl.ui.XDebuggerEntityConverter
 import com.intellij.xdebugger.XDebugSession
 import com.intellij.xdebugger.XDebugSessionListener
 import com.intellij.xdebugger.XDebuggerManager
+import com.intellij.xdebugger.impl.ui.DebuggerUIUtil
 import com.jetbrains.python.icons.PythonIcons
 import org.jetbrains.annotations.ApiStatus
 import java.lang.ref.WeakReference
@@ -103,12 +106,12 @@ internal class PyDebuggerBackendSwitcherAction : ComboBoxAction(), DumbAware {
       return
     }
 
-    if (!PyDebuggerBackendSwitcherVisibilityPin.isPinned(project)) {
-      val handlers = PyDebuggerBackendSwitchHandler.EP_NAME.extensionList
-      if (isPythonDapPluginInstalledAndEnabled() && handlers.all { !it.shouldShowSwitcher(project) }) {
-        e.presentation.isEnabledAndVisible = false
-        return
-      }
+    if (!isPyDebuggerBackendSwitcherVisible(project, e)) {
+      // Only the toolbar presence is in question here, so the action stays enabled: invoking it by id
+      // keeps working, which is how the backend is chosen before the first session exists.
+      e.presentation.isEnabled = true
+      e.presentation.isVisible = false
+      return
     }
 
     e.presentation.isEnabledAndVisible = true
@@ -254,6 +257,39 @@ internal class PyDebuggerBackendSwitcherAction : ComboBoxAction(), DumbAware {
 
 }
 
+/**
+ * Whether the backend switcher belongs on the Debug tool window tab the [e] context points at.
+ *
+ * The switcher lives in the tool window header, which is shared by every tab of every product that
+ * bundles the Python plugin, so it has to opt in per tab rather than default to visible: a C++ or a
+ * JavaScript session must not be told which Python debugger backend it runs on (CPP-51572).
+ */
+@ApiStatus.Internal
+fun isPyDebuggerBackendSwitcherVisible(project: Project, e: AnActionEvent): Boolean {
+  if (PyDebuggerBackendSwitcherVisibilityPin.isPinned(project)) return true
+
+  // While the PythonDAP plugin is installed, the handlers report whether the current editor and run
+  // configuration are Python at all, and a unanimous no hides the switcher. That is what keeps it off a
+  // notebook backed by a remote kernel.
+  val handlers = PyDebuggerBackendSwitchHandler.EP_NAME.extensionList
+  if (isPythonDapPluginInstalledAndEnabled() && handlers.all { !it.shouldShowSwitcher(project) }) return false
+
+  // Neither the pin nor the handlers look at the Debug tool window, which is why a C++ or a JavaScript tab
+  // kept the switcher. It belongs on Python and Jupyter tabs only, whether or not the plugin is installed:
+  // without it the switcher is the promotion surface for debugpy, and those tabs are where it belongs.
+  return isPythonDebugTab(e)
+}
+
+private fun isPythonDebugTab(e: AnActionEvent): Boolean {
+  // The header toolbar takes its data context from the selected tab, but a tab only publishes a run
+  // profile when it was started from an execution environment, which a Jupyter or console session
+  // was not. Those are recognized through the session instead: they run a pydevd-backed process.
+  if (e.getData(LangDataKeys.RUN_PROFILE) is AbstractPythonRunConfiguration<*>) return true
+  val sessionProxy = DebuggerUIUtil.getSessionProxy(e) ?: return false
+  val session = XDebuggerEntityConverter.getSession(sessionProxy) ?: return false
+  return session.runProfile is AbstractPythonRunConfiguration<*> || session.debugProcess is PyDebugProcess
+}
+
 /**
  * Returns the SDK of the currently selected run configuration, falling back to the project SDK.
  */