PY-36374 Clean up in ImportFromExistingAction and ImportCandidateHolder

* Remove some obsolete comments
* Simplify a redundant PECS signature
* Fix visibility of the fields in ImportFromExistingAction
* Make a precondition violation an IllegalArgumentException instead of assertion

GitOrigin-RevId: e37ea9974ac56f385f1993d6b953c522f564efe5

python/python-psi-impl/src/com/jetbrains/python/codeInsight/imports/ImportCandidateHolder.java

@@ -28,9 +28,9 @@ import java.util.List;
  *
  * @author dcheryasov
  */
-// visibility is intentionally package-level
 public class ImportCandidateHolder implements Comparable<ImportCandidateHolder> {
   private static final Logger LOG = Logger.getInstance(ImportCandidateHolder.class);
+
   @NotNull private final SmartPsiElementPointer<PsiNamedElement> myImportable;
   @Nullable private final SmartPsiElementPointer<PyImportElement> myImportElement;
   @NotNull private final SmartPsiElementPointer<PsiFileSystemItem> myFile;
@@ -49,10 +49,12 @@ public class ImportCandidateHolder implements Comparable<ImportCandidateHolder>
    *                      For top-level imported symbols it's <em>qualified name of containing module</em> (or package for __init__.py).
    *                      For modules and packages it should be <em>qualified name of their parental package</em>
    *                      (empty for modules and packages located at source roots).
-   *
    */
   public ImportCandidateHolder(@NotNull PsiNamedElement importable, @NotNull PsiFileSystemItem file,
                                @Nullable PyImportElement importElement, @Nullable QualifiedName path, @Nullable String asName) {
+    if (importElement == null && path == null) {
+      throw new IllegalArgumentException("Either an import path or an existing import should be provided for " + importable);
+    }
     SmartPointerManager pointerManager = SmartPointerManager.getInstance(importable.getProject());
     myFile = pointerManager.createSmartPsiElementPointer(file);
     myImportable = pointerManager.createSmartPsiElementPointer(importable);
@@ -63,7 +65,6 @@ public class ImportCandidateHolder implements Comparable<ImportCandidateHolder>
     myAsName = asName;
     myRelevance = PyCompletionUtilsKt.computeCompletionWeight(importable, myImportableName, myPath, null, false);
     LOG.debug("Computed relevance for import item ", myImportableName, ": ", myRelevance);
-    assert importElement != null || path != null; // one of these must be present
   }
 
   public ImportCandidateHolder(@NotNull PsiNamedElement importable, @NotNull PsiFileSystemItem file,

python/python-psi-impl/src/com/jetbrains/python/codeInsight/imports/ImportFromExistingAction.java

@@ -27,10 +27,10 @@ import static com.jetbrains.python.psi.PyUtil.as;
  * @author dcheryasov
  */
 public class ImportFromExistingAction implements QuestionAction {
-  PsiElement myTarget;
-  List<? extends ImportCandidateHolder> mySources; // list of <import, imported_item>
-  String myName;
-  boolean myUseQualifiedImport;
+  private final PsiElement myTarget;
+  private final List<ImportCandidateHolder> mySources;
+  private final String myName;
+  private final boolean myUseQualifiedImport;
   private Runnable myOnDoneCallback;
   private final boolean myImportLocally;
 
@@ -40,7 +40,7 @@ public class ImportFromExistingAction implements QuestionAction {
    * @param name relevant name ot the target element (e.g. of identifier in an expression).
    * @param useQualified if True, use qualified "import modulename" instead of "from modulename import ...".
    */
-  public ImportFromExistingAction(@NotNull PsiElement target, @NotNull List<? extends ImportCandidateHolder> sources, @NotNull String name,
+  public ImportFromExistingAction(@NotNull PsiElement target, @NotNull List<ImportCandidateHolder> sources, @NotNull String name,
                                   boolean useQualified, boolean importLocally) {
     myTarget = target;
     mySources = sources;