feat: Swift Language Support + bug fix + missing frontend build docs

[ayodm]

Summary

Three items bundled in this issue for discussion — happy to split into separate PRs if preferred.

1. Swift Language Support (feat)

I added Swift parsing support to Axon. Tested on a ~350-file Swift iOS project — successfully indexes 2988 symbols and 8351 relationships.

Constructs extracted:

• Symbols: functions, methods (including init), classes, structs, enums, protocols (→ interface), typealiases (→ type_alias), extensions (walked for methods, no separate symbol emitted)
• Imports: import Foundation, import UIKit, etc.
• Calls: direct calls (MyClass(name:)) and method calls (someObj.method())
• Type references: parameter types and return types from function signatures
• Heritage: class/struct inheritance and protocol conformance

Files changed:

• pyproject.toml — added tree-sitter-swift>=0.0.1 dependency
• src/axon/config/languages.py — added .swift → "swift" extension mapping
• src/axon/core/ingestion/parser_phase.py — registered SwiftParser in _PARSER_FACTORIES
• src/axon/core/parsers/swift.py — new file, full parser implementation (~400 lines)

tree-sitter-swift AST notes (useful for reviewers):

• class_declaration is reused for class, struct, enum, and extension — distinguished by the first keyword child
• protocol_declaration is separate from class_declaration
• Function names are in simple_identifier children (not a name field)
• Method calls use navigation_expression → navigation_suffix (not member_expression)
• protocol_function_declaration is distinct from function_declaration

2. Bug fix: max_workers crash on empty repos (fix)

process_imports() in src/axon/core/ingestion/imports.py crashes with ValueError: max_workers must be greater than 0 when parse_data is empty (e.g., a repo with no supported files).

# Before (crashes when len(parse_data) == 0)
workers = min(os.cpu_count() or 4, 8, len(parse_data))

# After
workers = max(1, min(os.cpu_count() or 4, 8, len(parse_data)))

3. Frontend build needed for axon ui (docs)

After a fresh pip install -e ., axon ui serves {"detail":"Not Found"} because the frontend hasn't been built. The dist/ directory is listed in pyproject.toml artifacts but isn't included in the repo or built during install.

Fix is to run:

cd src/axon/web/frontend && npm install && npm run build

This could be documented in the README or automated in the build process.

---

Code Changes

Diff of existing files

diff --git a/pyproject.toml b/pyproject.toml
index 3b0bfaf..613dbf0 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -27,6 +27,7 @@ dependencies = [
     "tree-sitter-python>=0.23.0",
     "tree-sitter-javascript>=0.23.0",
     "tree-sitter-typescript>=0.23.0",
+    "tree-sitter-swift>=0.0.1",
     "kuzu>=0.11.0",
     "igraph>=1.0.0",
     "leidenalg>=0.11.0",

diff --git a/src/axon/config/languages.py b/src/axon/config/languages.py
index bd34817..d4716e5 100644
--- a/src/axon/config/languages.py
+++ b/src/axon/config/languages.py
@@ -12,6 +12,7 @@ SUPPORTED_EXTENSIONS: dict[str, str] = {
     ".jsx": "javascript",
     ".mjs": "javascript",
     ".cjs": "javascript",
+    ".swift": "swift",
 }

diff --git a/src/axon/core/ingestion/imports.py b/src/axon/core/ingestion/imports.py
index 841d88e..dfe8e91 100644
--- a/src/axon/core/ingestion/imports.py
+++ b/src/axon/core/ingestion/imports.py
@@ -154,7 +154,7 @@ def process_imports(
     source_roots = _detect_source_roots(file_index)
 
     if parallel:
-        workers = min(os.cpu_count() or 4, 8, len(parse_data))
+        workers = max(1, min(os.cpu_count() or 4, 8, len(parse_data)))
         with ThreadPoolExecutor(max_workers=workers) as pool:

diff --git a/src/axon/core/ingestion/parser_phase.py b/src/axon/core/ingestion/parser_phase.py
index 93840e9..39558f4 100644
--- a/src/axon/core/ingestion/parser_phase.py
+++ b/src/axon/core/ingestion/parser_phase.py
@@ -26,6 +26,7 @@ from axon.core.graph.model import (
 from axon.core.parsers.base import LanguageParser, ParseResult
 from axon.core.parsers.python_lang import PythonParser
+from axon.core.parsers.swift import SwiftParser
 from axon.core.parsers.typescript import TypeScriptParser
 
@@ -45,6 +46,7 @@ _PARSER_FACTORIES: dict[str, Callable[[], LanguageParser]] = {
     "javascript": lambda: TypeScriptParser(dialect="javascript"),
+    "swift": SwiftParser,
 }

New file: src/axon/core/parsers/swift.py (~400 lines)

"""Swift language parser using tree-sitter.

Extracts functions, classes, structs, enums, protocols, methods, imports,
calls, type annotations, and inheritance relationships from Swift source code.
"""

from __future__ import annotations

import tree_sitter_swift as tsswift
from tree_sitter import Language, Node, Parser

from axon.core.parsers.base import (
    CallInfo,
    ImportInfo,
    LanguageParser,
    ParseResult,
    SymbolInfo,
    TypeRef,
)

SWIFT_LANGUAGE = Language(tsswift.language())

_BUILTIN_TYPES: frozenset[str] = frozenset(
    {
        "Int", "Int8", "Int16", "Int32", "Int64",
        "UInt", "UInt8", "UInt16", "UInt32", "UInt64",
        "Float", "Double", "Bool", "String", "Character",
        "Void", "Any", "AnyObject", "Never",
        "Optional", "Array", "Dictionary", "Set",
    }
)


class SwiftParser(LanguageParser):
    """Parses Swift source code using tree-sitter."""

    def __init__(self) -> None:
        self._parser = Parser(SWIFT_LANGUAGE)

    def parse(self, content: str, file_path: str) -> ParseResult:
        tree = self._parser.parse(content.encode("utf-8"))
        result = ParseResult()
        self._walk(tree.root_node, content, result, class_name="")
        return result

    def _walk(self, node, content, result, class_name):
        for child in node.children:
            ntype = child.type
            if ntype == "function_declaration":
                self._extract_function(child, content, result, class_name)
            elif ntype == "class_declaration":
                self._extract_class_like(child, content, result)
            elif ntype == "protocol_declaration":
                self._extract_protocol(child, content, result)
            elif ntype == "typealias_declaration":
                self._extract_typealias(child, content, result)
            elif ntype == "import_declaration":
                self._extract_import(child, result)
            elif ntype == "call_expression":
                self._extract_call(child, result)
            elif ntype == "init_declaration":
                self._extract_init(child, content, result, class_name)
            elif ntype == "protocol_function_declaration":
                self._extract_protocol_function(child, content, result, class_name)
            else:
                self._walk(child, content, result, class_name)

    # ... (full implementation in the linked file above)

Full file is ~400 lines following the same _extract_* pattern as the Python and TypeScript parsers. Handles Swift-specific AST quirks like class_declaration reuse and navigation_expression for method calls.

---

Happy to split these into separate issues/PRs, add tests in tests/core/test_parser_swift.py, or adjust scope based on your feedback.