Add support for parsing and merging AWS config and credentials files (smithy-lang#729)

Co-authored-by: Ujjwal <19787410+ubaskota@users.noreply.github.com>

Author: arandito

packages/smithy-aws-core/.changes/next-release/smithy-aws-core-breaking-daa90c9488264b4099ff3dc55606ed32.json

@@ -0,0 +1,4 @@
+{
+  "type": "feature",
+  "description": "Add utilities for parsing and merging shared AWS configuration and credentials files. These utilities are not yet integrated into generated clients."
+}

packages/smithy-aws-core/src/smithy_aws_core/config/__init__.py

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+# Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+# SPDX-License-Identifier: Apache-2.0
+
+import os
+from pathlib import Path
+
+from smithy_aws_core.config.file_parser import (
+    FileType,
+    parse_config_file,
+    standardize,
+)
+from smithy_aws_core.config.merged_config import MergedConfig
+
+_DEFAULT_CONFIG_FILE = "~/.aws/config"
+_DEFAULT_CREDENTIALS_FILE = "~/.aws/credentials"
+_CONFIG_FILE_ENV_VAR = "AWS_CONFIG_FILE"
+_CREDENTIALS_FILE_ENV_VAR = "AWS_SHARED_CREDENTIALS_FILE"
+
+
+def _resolve_config_paths(
+    config_file_path: Path | None = None,
+    credentials_file_path: Path | None = None,
+) -> tuple[Path, Path]:
+    """Resolve the final config and credentials file paths.
+
+    Resolution order for each path:
+    1. Explicit argument (if provided)
+    2. Environment variable (AWS_CONFIG_FILE / AWS_SHARED_CREDENTIALS_FILE)
+    3. Default (~/.aws/config / ~/.aws/credentials)
+
+    The ~ is expanded to the user's home directory.
+
+    :param config_file_path: Override path for config file.
+    :param credentials_file_path: Override path for credentials file.
+    :returns: Tuple of (resolved_config_path, resolved_credentials_path).
+    """
+    config_path = (
+        config_file_path
+        or Path(os.environ.get(_CONFIG_FILE_ENV_VAR, _DEFAULT_CONFIG_FILE))
+    ).expanduser()
+
+    credentials_path = (
+        credentials_file_path
+        or Path(os.environ.get(_CREDENTIALS_FILE_ENV_VAR, _DEFAULT_CREDENTIALS_FILE))
+    ).expanduser()
+
+    return config_path, credentials_path
+
+
+async def load_config(
+    config_file_path: Path | None = None,
+    credentials_file_path: Path | None = None,
+) -> MergedConfig:
+    """Load and merge AWS config and credentials files.
+
+    Parses both files, standardizes them, and returns a merged
+    MergedConfig ready for querying.
+
+    :param config_file_path: Override path for config file.
+        Defaults to AWS_CONFIG_FILE env var or ~/.aws/config.
+    :param credentials_file_path: Override path for credentials file.
+        Defaults to AWS_SHARED_CREDENTIALS_FILE env var or ~/.aws/credentials.
+    :returns: A MergedConfig with merged profiles from both files.
+    """
+
+    config_path, credentials_path = _resolve_config_paths(
+        config_file_path, credentials_file_path
+    )
+
+    raw_config = await parse_config_file(str(config_path))
+    raw_credentials = await parse_config_file(str(credentials_path))
+
+    std_config = standardize(raw_config, FileType.CONFIG)
+    std_credentials = standardize(raw_credentials, FileType.CREDENTIALS)
+
+    return MergedConfig(std_config, std_credentials)

packages/smithy-aws-core/src/smithy_aws_core/config/exceptions.py

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+# Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+# SPDX-License-Identifier: Apache-2.0
+
+"""Config related exceptions"""
+
+
+class ConfigParseError(Exception):
+    """Raised when a config file cannot be parsed due to invalid syntax."""