fix: generation of Python imports (#979)

Closes #974

### Summary of Changes

Fix the generation of Python imports. It now also works without explicit
imports or if stubs are declared in the same module.

packages/safe-ds-lang/src/language/generation/safe-ds-python-generator.ts

@@ -40,7 +40,6 @@ import {
     isSdsPipeline,
     isSdsPlaceholder,
     isSdsPrefixOperation,
-    isSdsQualifiedImport,
     isSdsReference,
     isSdsSegment,
     isSdsTemplateString,
@@ -49,7 +48,6 @@ import {
     isSdsTemplateStringPart,
     isSdsTemplateStringStart,
     isSdsWildcard,
-    isSdsWildcardImport,
     isSdsYield,
     SdsArgument,
     SdsAssignee,
@@ -64,17 +62,16 @@ import {
     SdsParameterList,
     SdsPipeline,
     SdsPlaceholder,
+    SdsReference,
     SdsSegment,
     SdsStatement,
 } from '../generated/ast.js';
-import { isInStubFile, isStubFile } from '../helpers/fileExtensions.js';
+import { isStubFile } from '../helpers/fileExtensions.js';
 import { IdManager } from '../helpers/idManager.js';
 import {
     getAbstractResults,
     getArguments,
     getAssignees,
-    getImportedDeclarations,
-    getImports,
     getModuleMembers,
     getParameters,
     getPlaceholderByName,
@@ -905,11 +902,9 @@ export class SafeDsPythonGenerator {
             }
         } else if (isSdsReference(expression)) {
             const declaration = expression.target.ref!;
-            const referenceImport =
-                this.getExternalReferenceNeededImport(expression, declaration) ||
-                this.getInternalReferenceNeededImport(expression, declaration);
+            const referenceImport = this.createImportDataForReference(expression);
             frame.addImport(referenceImport);
-            return traceToNode(expression)(referenceImport?.alias || this.getPythonNameOrDefault(declaration));
+            return traceToNode(expression)(referenceImport?.alias ?? this.getPythonNameOrDefault(declaration));
         }
         /* c8 ignore next 2 */
         throw new Error(`Unknown expression type: ${expression.$type}`);
@@ -1127,68 +1122,38 @@ export class SafeDsPythonGenerator {
         }${this.generateExpression(argument.value, frame)}`;
     }
 
-    private getExternalReferenceNeededImport(
-        expression: SdsExpression | undefined,
-        declaration: SdsDeclaration | undefined,
-    ): ImportData | undefined {
-        if (!expression || !declaration) {
+    private createImportDataForReference(reference: SdsReference): ImportData | undefined {
+        const target = reference.target.ref;
+        if (!target) {
             /* c8 ignore next 2 */
             return undefined;
         }
 
-        // Root Node is always a module.
-        const currentModule = <SdsModule>AstUtils.findRootNode(expression);
-        const targetModule = <SdsModule>AstUtils.findRootNode(declaration);
-        for (const value of getImports(currentModule)) {
-            // Verify same package
-            if (value.package !== targetModule.name) {
-                continue;
-            }
-            if (isSdsQualifiedImport(value)) {
-                const importedDeclarations = getImportedDeclarations(value);
-                for (const importedDeclaration of importedDeclarations) {
-                    if (declaration === importedDeclaration.declaration?.ref) {
-                        if (importedDeclaration.alias !== undefined) {
-                            return {
-                                importPath: this.getPythonModuleOrDefault(targetModule),
-                                declarationName: importedDeclaration.declaration?.ref?.name,
-                                alias: importedDeclaration.alias.alias,
-                            };
-                        } else {
-                            return {
-                                importPath: this.getPythonModuleOrDefault(targetModule),
-                                declarationName: importedDeclaration.declaration?.ref?.name,
-                            };
-                        }
-                    }
-                }
-            }
-            if (isSdsWildcardImport(value)) {
-                return {
-                    importPath: this.getPythonModuleOrDefault(targetModule),
-                    declarationName: declaration.name,
-                };
+        const sourceModule = <SdsModule>AstUtils.findRootNode(reference);
+        const targetModule = <SdsModule>AstUtils.findRootNode(target);
+
+        // Compute import path
+        let importPath: string | undefined = undefined;
+        if (isSdsPipeline(target) || isSdsSegment(target)) {
+            if (sourceModule !== targetModule) {
+                importPath = `${this.getPythonModuleOrDefault(targetModule)}.${this.formatGeneratedFileName(
+                    this.getModuleFileBaseName(targetModule),
+                )}`;
             }
+        } else if (isSdsModule(target.$container)) {
+            importPath = this.getPythonModuleOrDefault(targetModule);
         }
-        return undefined;
-    }
 
-    private getInternalReferenceNeededImport(
-        expression: SdsExpression,
-        declaration: SdsDeclaration,
-    ): ImportData | undefined {
-        // Root Node is always a module.
-        const currentModule = <SdsModule>AstUtils.findRootNode(expression);
-        const targetModule = <SdsModule>AstUtils.findRootNode(declaration);
-        if (currentModule !== targetModule && !isInStubFile(targetModule)) {
+        if (importPath) {
+            const refText = reference.target.$refText;
             return {
-                importPath: `${this.getPythonModuleOrDefault(targetModule)}.${this.formatGeneratedFileName(
-                    this.getModuleFileBaseName(targetModule),
-                )}`,
-                declarationName: this.getPythonNameOrDefault(declaration),
+                importPath,
+                declarationName: this.getPythonNameOrDefault(target),
+                alias: refText === target.name ? undefined : refText,
             };
+        } else {
+            return undefined;
         }
-        return undefined;
     }
 
     private getModuleFileBaseName(module: SdsModule): string {

packages/safe-ds-lang/tests/resources/generation/python/declarations/parameter with python name/generated/tests/generator/parameterWithPythonName/gen_input.py

@@ -1,3 +1,7 @@
+# Imports ----------------------------------------------------------------------
+
+from tests.generator.parameterWithPythonName import f1, f2
+
 # Segments ---------------------------------------------------------------------
 
 def test(param1, param_2, param_3=0):

packages/safe-ds-lang/tests/resources/generation/python/declarations/pipeline with python name/generated/tests/generator/pipelineWithPythonName/gen_input.py

@@ -1,3 +1,7 @@
+# Imports ----------------------------------------------------------------------
+
+from tests.generator.pipelineWithPythonName import f
+
 # Pipelines --------------------------------------------------------------------
 
 def test_pipeline():

packages/safe-ds-lang/tests/resources/generation/python/declarations/segment with python name/generated/tests/generator/segmentWithPythonName/gen_input.py

@@ -1,3 +1,7 @@
+# Imports ----------------------------------------------------------------------
+
+from tests.generator.segmentWithPythonName import f
+
 # Segments ---------------------------------------------------------------------
 
 def test_segment():

packages/safe-ds-lang/tests/resources/generation/python/declarations/two pipelines/generated/tests/generator/twoPipelines/gen_input.py

@@ -1,3 +1,7 @@
+# Imports ----------------------------------------------------------------------
+
+from tests.generator.twoPipelines import f
+
 # Pipelines --------------------------------------------------------------------
 
 def test1():

packages/safe-ds-lang/tests/resources/generation/python/declarations/two segments/generated/tests/generator/twoSegments/gen_input.py

@@ -1,3 +1,7 @@
+# Imports ----------------------------------------------------------------------
+
+from tests.generator.twoSegments import f
+
 # Segments ---------------------------------------------------------------------
 
 def test1(a, b=0):

packages/safe-ds-lang/tests/resources/generation/python/expressions/block lambda result/generated/tests/generator/blockLambdaResult/gen_input.py

@@ -1,3 +1,7 @@
+# Imports ----------------------------------------------------------------------
+
+from tests.generator.blockLambdaResult import g, h
+
 # Segments ---------------------------------------------------------------------
 
 def f1(l):

packages/safe-ds-lang/tests/resources/generation/python/expressions/block lambda/generated/tests/generator/blockLambda/gen_input.py

@@ -1,3 +1,7 @@
+# Imports ----------------------------------------------------------------------
+
+from tests.generator.blockLambda import f1, f2, f3, g, g2
+
 # Pipelines --------------------------------------------------------------------
 
 def test():

packages/safe-ds-lang/tests/resources/generation/python/expressions/call/generated/tests/generator/call/gen_input.py

@@ -1,5 +1,6 @@
 # Imports ----------------------------------------------------------------------
 
+from tests.generator.call import f, g, h, i, j, k
 from typing import Any, Callable, TypeVar
 
 # Type variables ---------------------------------------------------------------

packages/safe-ds-lang/tests/resources/generation/python/expressions/constant/generated/tests/generator/constant/gen_input.py

@@ -1,3 +1,7 @@
+# Imports ----------------------------------------------------------------------
+
+from tests.generator.constant import f
+
 # Pipelines --------------------------------------------------------------------
 
 def test():

packages/safe-ds-lang/tests/resources/generation/python/expressions/enum variant call/generated/tests/generator/enumVariantCall/gen_input.py

@@ -1,3 +1,7 @@
+# Imports ----------------------------------------------------------------------
+
+from tests.generator.enumVariantCall import f, MyEnum
+
 # Pipelines --------------------------------------------------------------------
 
 def test():

packages/safe-ds-lang/tests/resources/generation/python/expressions/expression lambda/generated/tests/generator/expressionLambda/gen_input.py

@@ -1,3 +1,7 @@
+# Imports ----------------------------------------------------------------------
+
+from tests.generator.expressionLambda import f
+
 # Pipelines --------------------------------------------------------------------
 
 def test():

packages/safe-ds-lang/tests/resources/generation/python/expressions/indexed access/generated/tests/generator/indexedAccess/gen_input.py

@@ -1,5 +1,6 @@
 # Imports ----------------------------------------------------------------------
 
+from tests.generator.indexedAccess import f
 from typing import Any, TypeVar
 
 # Type variables ---------------------------------------------------------------

packages/safe-ds-lang/tests/resources/generation/python/expressions/infix operation/generated/tests/generator/infixOperation/gen_input.py

@@ -1,5 +1,6 @@
 # Imports ----------------------------------------------------------------------
 
+from tests.generator.infixOperation import f, g, h, i
 from typing import TypeVar
 
 # Type variables ---------------------------------------------------------------