Feature: Add an option to generate exceptions for Conjure errors

conjure-python-core/src/main/java/com/palantir/conjure/python/ConjurePythonGenerator.java

@@ -42,6 +42,7 @@
 import com.palantir.conjure.python.processors.typename.PackagePrependingTypeNameProcessor;
 import com.palantir.conjure.python.processors.typename.TypeNameProcessor;
 import com.palantir.conjure.python.types.DefinitionImportTypeDefinitionVisitor;
+import com.palantir.conjure.python.types.PythonErrorGenerator;
 import com.palantir.conjure.python.types.PythonTypeGenerator;
 import com.palantir.conjure.spec.ConjureDefinition;
 import com.palantir.conjure.spec.TypeName;
@@ -146,6 +147,12 @@ private PythonFile getImplPythonFile(
                 definitionPackageNameProcessor,
                 definitionTypeNameProcessor,
                 dealiasingTypeVisitor);
+        PythonErrorGenerator errorGenerator = new PythonErrorGenerator(
+                implPackageNameProcessor,
+                implTypeNameProcessor,
+                definitionPackageNameProcessor,
+                definitionTypeNameProcessor,
+                dealiasingTypeVisitor);
 
         List<PythonSnippet> snippets = new ArrayList<>();
         snippets.addAll(conjureDefinition.getTypes().stream()
@@ -154,6 +161,11 @@ private PythonFile getImplPythonFile(
         snippets.addAll(conjureDefinition.getServices().stream()
                 .map(clientGenerator::generateClient)
                 .toList());
+        if (config.generateErrorTypes()) {
+            snippets.addAll(conjureDefinition.getErrors().stream()
+                    .map(errorGenerator::generateError)
+                    .toList());
+        }
 
         Map<PythonPackage, List<PythonSnippet>> snippetsByPackage =
                 snippets.stream().collect(Collectors.groupingBy(PythonSnippet::pythonPackage));
@@ -203,6 +215,19 @@ private List<PythonFile> getInitFiles(
             importsByPackage.put(pythonPackage, pythonImport);
         });
 
+        if (config.generateErrorTypes()) {
+            conjureDefinition.getErrors().forEach(errorDefinition -> {
+                PythonPackage pythonPackage = PythonPackage.of(definitionPackageNameProcessor.process(
+                        errorDefinition.getErrorName().getPackage()));
+                PythonImport pythonImport = PythonImport.of(
+                        moduleSpecifier,
+                        NamedImport.of(
+                                implTypeNameProcessor.process(errorDefinition.getErrorName()),
+                                definitionTypeNameProcessor.process(errorDefinition.getErrorName())));
+                importsByPackage.put(pythonPackage, pythonImport);
+            });
+        }
+
         return KeyedStream.stream(importsByPackage.build().asMap())
                 .map((pythonPackage, imports) -> {
                     List<String> importNames = imports.stream()

conjure-python-core/src/main/java/com/palantir/conjure/python/GeneratorConfiguration.java

@@ -43,6 +43,11 @@ public interface GeneratorConfiguration {
 
     boolean generateRawSource();
 
+    @Value.Default
+    default boolean generateErrorTypes() {
+        return false;
+    }
+
     default Optional<String> pythonicPackageName() {
         return packageName().map(packageName -> packageName.replace('-', '_'));
     }

conjure-python-core/src/main/java/com/palantir/conjure/python/poet/ErrorSnippet.java

@@ -0,0 +1,179 @@
+/*
+ * (c) Copyright 2025 Palantir Technologies Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.palantir.conjure.python.poet;
+
+import com.google.common.collect.ImmutableList;
+import com.palantir.conjure.python.processors.PythonIdentifierSanitizer;
+import com.palantir.conjure.python.types.ImportTypeVisitor;
+import com.palantir.conjure.spec.Documentation;
+import java.util.List;
+import java.util.Optional;
+import org.immutables.value.Value;
+
+@Value.Immutable
+public interface ErrorSnippet extends PythonSnippet {
+    ImmutableList<PythonImport> DEFAULT_IMPORTS = ImmutableList.of(
+            PythonImport.builder()
+                    .moduleSpecifier(ImportTypeVisitor.CONJURE_PYTHON_CLIENT)
+                    .addNamedImports(NamedImport.of("ConjureHTTPError"))
+                    .build(),
+            PythonImport.builder()
+                    .moduleSpecifier(ImportTypeVisitor.TYPING)
+                    .addNamedImports(NamedImport.of("TypedDict"))
+                    .build());
+
+    @Override
+    @Value.Default
+    default String idForSorting() {
+        return className();
+    }
+
+    String className();
+
+    String definitionName();
+
+    PythonPackage definitionPackage();
+
+    Optional<Documentation> docs();
+
+    String errorCode();
+
+    String namespace();
+
+    List<PythonField> safeArgs();
+
+    List<PythonField> unsafeArgs();
+
+    @Override
+    default void emit(PythonPoetWriter poetWriter) {
+        poetWriter.writeIndentedLine(String.format("class %s(ConjureHTTPError):", className()));
+        poetWriter.increaseIndent();
+        docs().ifPresent(poetWriter::writeDocs);
+
+        poetWriter.writeLine();
+
+        // Error constants
+        poetWriter.writeIndentedLine(String.format("ERROR_CODE = \"%s\"", errorCode()));
+        poetWriter.writeIndentedLine(String.format("ERROR_NAMESPACE = \"%s\"", namespace()));
+        poetWriter.writeIndentedLine(String.format("ERROR_NAME = \"%s\"", definitionName()));
+
+        poetWriter.writeLine();
+
+        // args
+        emitTypedDict(poetWriter, "SafeArgs", safeArgs());
+        emitTypedDict(poetWriter, "UnsafeArgs", unsafeArgs());
+
+        emitConstructor(poetWriter);
+
+        // classmethods
+        emitIsInstanceMethod(poetWriter);
+        emitFromErrorMethod(poetWriter);
+
+        // end of class def
+        poetWriter.decreaseIndent();
+        poetWriter.writeLine();
+        poetWriter.writeLine();
+
+        PythonClassRenamer.renameClass(poetWriter, className(), definitionPackage(), definitionName());
+    }
+
+    default void emitTypedDict(PythonPoetWriter poetWriter, String typedDictName, List<PythonField> fields) {
+        if (fields.isEmpty()) {
+            return;
+        }
+        poetWriter.writeIndentedLine(String.format("class %s(TypedDict):", typedDictName));
+        poetWriter.increaseIndent();
+        for (PythonField field : fields) {
+            poetWriter.writeIndentedLine(String.format(
+                    "%s: %s", PythonIdentifierSanitizer.sanitize(field.attributeName()), field.myPyType()));
+        }
+        poetWriter.decreaseIndent();
+        poetWriter.writeLine();
+    }
+
+    default void emitConstructor(PythonPoetWriter poetWriter) {
+        poetWriter.writeIndentedLine("def __init__(self, base_error: ConjureHTTPError) -> None:");
+        poetWriter.increaseIndent();
+        poetWriter.writeIndentedLine("super().__init__(");
+        poetWriter.increaseIndent();
+        poetWriter.writeIndentedLine("status_code=base_error.status_code,");
+        // TODO(bzhang): Use enum once https://github.com/palantir/conjure-python-client/pull/171 is merged
+        poetWriter.writeIndentedLine("error_code=base_error.error_code,");
+        poetWriter.writeIndentedLine("error_name=base_error.error_name,");
+        poetWriter.writeIndentedLine("error_instance_id=base_error.error_instance_id,");
+        poetWriter.writeIndentedLine("parameters=base_error.parameters");
+        poetWriter.decreaseIndent();
+        poetWriter.writeIndentedLine(")");
+
+        emitArgsParser(poetWriter, "safe_args", "SafeArgs", safeArgs());
+        emitArgsParser(poetWriter, "unsafe_args", "UnsafeArgs", unsafeArgs());
+
+        poetWriter.decreaseIndent();
+        poetWriter.writeLine();
+    }
+
+    default void emitArgsParser(
+            PythonPoetWriter poetWriter, String fieldName, String typeName, List<PythonField> fields) {
+        if (fields.isEmpty()) {
+            return;
+        }
+        poetWriter.writeIndentedLine(String.format("self.%s: %s.%s = {", fieldName, className(), typeName));
+        poetWriter.increaseIndent();
+        for (int i = 0; i < fields.size(); i++) {
+            PythonField field = fields.get(i);
+            String comma = i == fields.size() - 1 ? "" : ",";
+            poetWriter.writeIndentedLine(String.format(
+                    "'%s': base_error.parameters['%s']%s",
+                    PythonIdentifierSanitizer.sanitize(field.attributeName()), field.jsonIdentifier(), comma));
+        }
+        poetWriter.decreaseIndent();
+        poetWriter.writeIndentedLine("}");
+    }
+
+    default void emitIsInstanceMethod(PythonPoetWriter poetWriter) {
+        poetWriter.writeIndentedLine("@classmethod");
+        poetWriter.writeIndentedLine("def is_instance(cls, error: ConjureHTTPError) -> bool:");
+        poetWriter.increaseIndent();
+        poetWriter.writeIndentedLine("return (");
+        poetWriter.increaseIndent();
+        poetWriter.writeIndentedLine("error.error_name == cls.ERROR_NAME and");
+        poetWriter.writeIndentedLine("error.error_code == cls.ERROR_CODE");
+        poetWriter.decreaseIndent();
+        poetWriter.writeIndentedLine(")");
+        poetWriter.decreaseIndent();
+        poetWriter.writeLine();
+    }
+
+    default void emitFromErrorMethod(PythonPoetWriter poetWriter) {
+        poetWriter.writeIndentedLine("@classmethod");
+        poetWriter.writeIndentedLine(
+                String.format("def from_error(cls, error: ConjureHTTPError) -> '%s':", className()));
+        poetWriter.increaseIndent();
+        poetWriter.writeIndentedLine("if not cls.is_instance(error):");
+        poetWriter.increaseIndent();
+        poetWriter.writeIndentedLine("raise ValueError(f\"Error is not a {cls.ERROR_NAME}\")");
+        poetWriter.decreaseIndent();
+        poetWriter.writeIndentedLine("return cls(error)");
+        poetWriter.decreaseIndent();
+    }
+
+    class Builder extends ImmutableErrorSnippet.Builder {}
+
+    static Builder builder() {
+        return new Builder();
+    }
+}

conjure-python-core/src/main/java/com/palantir/conjure/python/types/PythonErrorGenerator.java

@@ -0,0 +1,114 @@
+/*
+ * (c) Copyright 2025 Palantir Technologies Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.palantir.conjure.python.types;
+
+import com.palantir.conjure.CaseConverter;
+import com.palantir.conjure.python.poet.ErrorSnippet;
+import com.palantir.conjure.python.poet.PythonField;
+import com.palantir.conjure.python.poet.PythonImport;
+import com.palantir.conjure.python.poet.PythonPackage;
+import com.palantir.conjure.python.processors.packagename.PackageNameProcessor;
+import com.palantir.conjure.python.processors.typename.TypeNameProcessor;
+import com.palantir.conjure.spec.ErrorDefinition;
+import com.palantir.conjure.visitor.DealiasingTypeVisitor;
+import com.palantir.conjure.visitor.TypeVisitor;
+import java.util.List;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+public final class PythonErrorGenerator {
+
+    private final PackageNameProcessor implPackageNameProcessor;
+    private final TypeNameProcessor implTypeNameProcessor;
+    private final PackageNameProcessor definitionPackageNameProcessor;
+    private final TypeNameProcessor definitionTypeNameProcessor;
+    private final DealiasingTypeVisitor dealiasingTypeVisitor;
+    private final PythonTypeNameVisitor pythonTypeNameVisitor;
+    private final MyPyTypeNameVisitor myPyTypeNameVisitor;
+
+    public PythonErrorGenerator(
+            PackageNameProcessor implPackageNameProcessor,
+            TypeNameProcessor implTypeNameProcessor,
+            PackageNameProcessor definitionPackageNameProcessor,
+            TypeNameProcessor definitionTypeNameProcessor,
+            DealiasingTypeVisitor dealiasingTypeVisitor) {
+        this.implPackageNameProcessor = implPackageNameProcessor;
+        this.implTypeNameProcessor = implTypeNameProcessor;
+        this.definitionPackageNameProcessor = definitionPackageNameProcessor;
+        this.definitionTypeNameProcessor = definitionTypeNameProcessor;
+        this.dealiasingTypeVisitor = dealiasingTypeVisitor;
+        this.pythonTypeNameVisitor = new PythonTypeNameVisitor(implTypeNameProcessor);
+        this.myPyTypeNameVisitor = new MyPyTypeNameVisitor(dealiasingTypeVisitor, implTypeNameProcessor);
+    }
+
+    public ErrorSnippet generateError(ErrorDefinition errorDef) {
+        ImportTypeVisitor importVisitor =
+                new ImportTypeVisitor(errorDef.getErrorName(), implTypeNameProcessor, implPackageNameProcessor);
+
+        // Collect imports from all field types
+        Set<PythonImport> imports = errorDef.getSafeArgs().stream()
+                .flatMap(entry -> entry.getType().accept(importVisitor).stream())
+                .collect(Collectors.toSet());
+        imports.addAll(errorDef.getUnsafeArgs().stream()
+                .flatMap(entry -> entry.getType().accept(importVisitor).stream())
+                .collect(Collectors.toSet()));
+
+        // Convert safe args to PythonFields
+        List<PythonField> safeArgs = errorDef.getSafeArgs().stream()
+                .map(entry -> PythonField.builder()
+                        .attributeName(CaseConverter.toCase(entry.getFieldName().get(), CaseConverter.Case.SNAKE_CASE))
+                        .jsonIdentifier(entry.getFieldName().get())
+                        .docs(entry.getDocs())
+                        .pythonType(entry.getType().accept(pythonTypeNameVisitor))
+                        .myPyType(entry.getType().accept(myPyTypeNameVisitor))
+                        .isOptional(dealiasingTypeVisitor
+                                .dealias(entry.getType())
+                                .fold(_typeDefinition -> false, type -> type.accept(TypeVisitor.IS_OPTIONAL)))
+                        .build())
+                .collect(Collectors.toList());
+
+        // Convert unsafe args to PythonFields
+        List<PythonField> unsafeArgs = errorDef.getUnsafeArgs().stream()
+                .map(entry -> PythonField.builder()
+                        .attributeName(CaseConverter.toCase(entry.getFieldName().get(), CaseConverter.Case.SNAKE_CASE))
+                        .jsonIdentifier(entry.getFieldName().get())
+                        .docs(entry.getDocs())
+                        .pythonType(entry.getType().accept(pythonTypeNameVisitor))
+                        .myPyType(entry.getType().accept(myPyTypeNameVisitor))
+                        .isOptional(dealiasingTypeVisitor
+                                .dealias(entry.getType())
+                                .fold(_typeDefinition -> false, type -> type.accept(TypeVisitor.IS_OPTIONAL)))
+                        .build())
+                .collect(Collectors.toList());
+
+        return ErrorSnippet.builder()
+                .pythonPackage(PythonPackage.of(
+                        implPackageNameProcessor.process(errorDef.getErrorName().getPackage())))
+                .className(implTypeNameProcessor.process(errorDef.getErrorName()))
+                .definitionPackage(PythonPackage.of(definitionPackageNameProcessor.process(
+                        errorDef.getErrorName().getPackage())))
+                .definitionName(definitionTypeNameProcessor.process(errorDef.getErrorName()))
+                .addAllImports(ErrorSnippet.DEFAULT_IMPORTS)
+                .addAllImports(imports)
+                .docs(errorDef.getDocs())
+                .errorCode(errorDef.getCode().toString())
+                .namespace(errorDef.getNamespace().toString())
+                .safeArgs(safeArgs)
+                .unsafeArgs(unsafeArgs)
+                .build();
+    }
+}

conjure-python-core/src/test/java/com/palantir/conjure/python/ConjurePythonGeneratorTest.java

@@ -44,6 +44,7 @@ public final class ConjurePythonGeneratorTest {
             .generatorVersion("0.0.0")
             .shouldWriteCondaRecipe(true)
             .generateRawSource(false)
+            .generateErrorTypes(true)
             .build());
     private final InMemoryPythonFileWriter pythonFileWriter = new InMemoryPythonFileWriter();