sphinxcontrib-nexus 0.14.0

Unified code + documentation knowledge graph from Sphinx builds and Python AST analysis

sphinxcontrib-nexus

A unified code + documentation knowledge graph extracted from Sphinx builds and Python AST analysis. Queryable via MCP, CLI, and Python API.

What makes it unique: Nexus is the only tool that puts code structure (call graphs, imports, inheritance, type annotations) and documentation structure (equations, cross-references, citations, theory pages) in the same graph. This enables queries that are impossible with code-only or doc-only tools — like tracing from a literature citation through an equation to the function that implements it.

Quick Start

pip install sphinxcontrib-nexus

As a Sphinx Extension

Add to your docs/conf.py:

extensions = ['sphinxcontrib.nexus']

After sphinx-build, find the graph at <outdir>/_nexus/graph.db (SQLite) and <outdir>/_nexus/graph.json.

Standalone AST Analysis (no Sphinx needed)

nexus analyze src/ --db graph.db

MCP Server (for Claude Code / AI agents)

nexus serve --db graph.db --project-root /path/to/project

Install Skills + MCP Server for Claude Code

nexus setup           # project-level: .mcp.json + .claude/skills/
nexus setup --global  # user-level: ~/.claude.json + ~/.claude/skills/ (all projects)

Ingest a Paper

nexus ingest paper.pdf --db graph.db     # extracts concepts, equations, citations via LLM

Interactive Graph Visualizer

nexus visualize --db graph.db            # opens HTML graph explorer in browser

Configuration

Config value	Default	Description
nexus_output	_nexus	Output directory relative to build output
nexus_ast_analyze	True	Run AST analysis during Sphinx build
nexus_max_viz_nodes	300	Max nodes in auto-generated graph.html
nexus_extra_source_dirs	[]	Extra directories (relative to project root) to analyze in addition to autodetected source roots. Useful for out-of-tree test suites or separate module roots.
nexus_analyze_tests	True	Whether Python test modules are merged into the graph. Set to False to exclude them entirely (e.g. to keep coverage numbers focused on production code).
nexus_test_patterns	["tests/*", "*/tests/*", "test_*.py", "*/test_*.py"]	Glob patterns (POSIX, evaluated with fnmatch against the path relative to each source dir) identifying Python test modules. Used both by nexus_analyze_tests=False exclusion and by the is_test flag on function nodes — a function is marked as a test only when its name follows the test/test_* convention and it lives in a file matching one of these patterns.
nexus_source_exclude_patterns	[]	Extra glob patterns (POSIX, same fnmatch semantics as nexus_test_patterns) listing directories or files to exclude from AST analysis entirely. Use this for tutorial scripts, vendored copies, legacy modules, or any other source that lives in the project tree but should not contribute nodes or edges to the graph. Patterns are applied in addition to the always-on base exclusions (docs/*, .venv/*, __pycache__/*) and to nexus_test_patterns when nexus_analyze_tests=False.
nexus_infer_implements	True	Whether to run the token-intersection heuristic in merge._infer_implements. Set False when explicit registry / marker / directive coverage is complete and the heuristic's inferred edges are noise.
nexus_verification_registry	[]	List of paths (relative to conf.py) to YAML files declaring explicit verification and implementation edges. See schema version 1 in the README's V&V section. Missing nodes are logged and skipped; schema errors raise RegistryError at build time.

Supported Project Layouts

Nexus works with any Python project:

• Standard packages: myproject/mypackage/__init__.py — detected automatically
• src layout: src/mypackage/ — detected automatically
• Flat modules: directories with .py files but no __init__.py — detected automatically
• Custom sys.path: projects that add directories to sys.path in conf.py — picked up from the Sphinx build environment

What the Graph Contains

Node Types (14)

Type	Source	Example
file	Sphinx	RST/doc pages
section	Sphinx	Labeled sections (:ref: targets)
equation	Sphinx	Labeled math equations (:eq: targets)
term	Sphinx	Glossary terms
function	Sphinx + AST	Python functions
class	Sphinx + AST	Python classes
method	Sphinx + AST	Python methods
attribute	Sphinx + AST	Class attributes
module	Sphinx + AST	Python modules
data	Sphinx	Module-level data
exception	Sphinx	Exception classes
type	Sphinx	Type aliases
external	Auto-detected	stdlib, builtins, installed packages (numpy, scipy, ...)
unresolved	Auto-detected	Referenced but not documented symbols

Edge Types (13)

Edge	Meaning	Source
contains	Parent → child (toctree, module→function, class→method)	Sphinx + AST
references	Cross-reference (:ref:, :term:)	Sphinx
documents	Doc page → code symbol (:func:, :class:)	Sphinx
equation_ref	Doc → equation (:eq:)	Sphinx
cites	Doc → citation	Sphinx
implements	Code → equation (inferred from co-occurrence in docs)	Merge
calls	Function → function	AST
imports	Module → module	AST
inherits	Class → parent class	AST
type_uses	Function → type (from annotations)	AST
tests	Test → tested function	AST
derives	Derivation → equation	AST
discriminates_on	Function → tag it branches on (if x == "...", match)	AST

MCP Tools (33)

Exploration

• query — keyword search across node names
• node_at — map a file position (LSP result, stack trace) to the innermost enclosing graph node; warns when the file changed since the graph was built (positions in a snapshot drift with edits)
• context — 360-degree view of a symbol: connections grouped by type, each bucket most-connected-first and token-budgeted (limit_per_type, default 25; honest omitted counts — a hub node's full context is megabytes)
• neighbors — direct connections with direction and type filtering
• callers — functions that call a given node (optionally transitive)
• callees — functions called by a given node (optionally transitive)
• shortest_path — how two concepts connect
• god_nodes — most connected nodes (entry points)
• stats — graph-level statistics

Safety & Refactoring

• impact — blast radius analysis (what breaks if you change X); depth buckets token-budgeted (limit_per_depth, default 50) while total_affected stays the true count
• detect_changes — map git diff to affected symbols
• rename — safe multi-file rename with confidence tagging
• retest — minimum set of tests to re-run after changes
• communities — detect functional groupings with cohesion scores
• graph_query — Cypher-like pattern matching ("function -calls-> function")
• bridges — find architectural hotspots connecting communities
• native_place — functions that may belong inside a class (Feature-Envy / "native place"): every non-test caller is a method of one class. Ranked by strength (genuine relocations first, cross-module before same-module, private before public); public functions tested at least as much as used in production are flagged likely_free_primitive and ranked last (a verified free-function primitive is correctly free)
• twin_paths — independent implementations of the same computation (Type-2/3 clones / single-source-of-truth violations): function bodies sharing a high fraction of AST structural shingles where neither calls the other. The fingerprint captures the array math (@, einsum, slicing) the call graph cannot see; cross-module pairs ranked first
• discriminations — tags discriminated at multiple sites (candidate missing types): the same string/enum tag (if geometry == "...", match kind:) branched on by many functions. Makes the coding-elegance smell "a repeated conditional is a missing type — discriminate once, at the boundary" machine-checkable; ranked by site fan-in
• dead_functions — functions/methods with no static callers (dead-code candidates): zero incoming calls edges from non-test code. A candidate list, not a verdict (dynamic dispatch is invisible to the static graph); public/decorated flags carry the false-positive sources, private+undecorated ranked first
• protocol_conformers — classes satisfying a Protocol's method-set without declaring it: Protocols are satisfied structurally but inherits records only explicit subclassing, so a structural conformer has no edge. Matches by method-name set (a heuristic — the type checker / LSP goToImplementation is authoritative)

Code + Doc Fusion (unique to Nexus)

• provenance_chain — citation → equation → code traceability
• verification_coverage — equation → code → test coverage map (supports limit/offset pagination)
• verification_audit — complete V&V audit: coverage + staleness + prioritized gap list (supports group_by and include_tests)
• verification_gaps — untagged tests, unverified equations, missing err catchers (supports module and level filters)
• staleness — detect docs that drifted from code
• session_briefing — AI agent context restoration
• trace_error — trace from failing test to equations on call path
• migration_plan — plan dependency migration with phased blast radius
• ingest — LLM-powered paper/PDF ingestion into the graph
• processes — detect named execution flows through the codebase (supports limit/offset pagination)

Workspaces (git worktrees)

• workspaces — list every checkout of the project (main tree + linked git worktrees) with branch, graph presence, and build provenance
• use_workspace — switch the server to the graph built inside another checkout, referenced by worktree name, branch name, or absolute root path (per-session; auto-reload follows)

Node results from AST-derived symbols carry file_path and lineno, so any query answer can be fed straight back to an editor, LSP request, or file read — the position → node bridge (node_at) runs in both directions.

Edit-time file brief (the ambient channel)

nexus file-brief path/to/module.py --db _nexus/graph.db --project-root .

Prints ≤6 lines of graph context for one source file — node count and external callers, the highest-degree node's copy-pasteable ID, the equations the file implements and how many tests verify them, the doc pages documenting it, and a staleness flag when the file changed since the graph was built. It reads the SQLite database directly (no graph load, ~100 ms warm), which makes it cheap enough to wire into an edit-time hook (e.g. a Claude Code PostToolUse hook on Edit|Write): graph context then arrives WITH every edit, the way a language server pushes diagnostics, instead of waiting to be asked. --json emits the full structured brief.

Usage journal

Every tool call appends one JSON line to ~/.nexus/usage.jsonl (timestamp, tool, args, duration, outcome, active workspace) so tool adoption can be evaluated from recorded behavior. Set NEXUS_USAGE_LOG=<path> to relocate it, or set it empty to disable. Journaling never blocks or fails a tool call.

MCP Resources (4)

Resource	Content
nexus://graph/stats	Node/edge counts by type
nexus://graph/communities	Functional area summaries
nexus://graph/schema	Node types, edge types, ID format
nexus://briefing	Session briefing for AI agents

Skills (9)

Installed via nexus setup. Each skill triggers on natural language:

Skill	Triggers on
nexus-exploring	"How does X work?", "What calls this?"
nexus-impact	"Is it safe to change X?", "What tests to re-run?"
nexus-debugging	"Why is X failing?", "Which equation is wrong?"
nexus-refactoring	"Rename this", "Extract this into a module"
nexus-verification	"What's verified?", "Which docs are stale?"
nexus-migration	"Plan numpy→jax migration"
nexus-guide	"What Nexus tools are available?"
nexus-cli	"Analyze the codebase", "Start the server"
behavioral-auto-regression	"Agent is using Grep instead of Nexus", "Tool selection is wrong"

V&V Integration

Nexus turns pytest markers, RST directives, and repository-level YAML into typed verification edges in the graph, so audit tools can answer "which equations are actually verified, and by which tests, at what V&V level?" without hand-wiring.

From pytest markers (zero config)

Add standard pytest markers to your tests and they flow through to the graph automatically:

import pytest

@pytest.mark.l0
@pytest.mark.verifies("transport-cartesian")
@pytest.mark.catches("FM-07")
def test_attenuation_vacuum_source():
    ...

After the next Sphinx build, the corresponding test node carries vv_level="L0", verifies=("transport-cartesian",), and catches=("FM-07",) in its metadata. A merge.write_verifies_edges pass then walks every function with a verifies tuple and emits real EdgeType.TESTS edges from the test to math:equation:transport-cartesian. Class-level and module-level pytestmark declarations propagate to contained test methods (gated on is_test=True — private helpers don't inherit).

The @verify.l0(equations=[...], catches=[...]) sugar form is also recognized.

From RST directives

Declare verification edges directly in theory prose:

.. math::
   :label: transport-cartesian

   \dots

.. implements:: transport-cartesian
   :by: orpheus.sn.solve_sn

.. verifies:: transport-cartesian
   :by: tests.test_sn.test_transport

Both directives accept an explicit :by: option naming the Python symbol. When omitted, they fall back to inspecting env.ref_context so usage nested inside .. py:function:: / .. autofunction:: blocks picks up the enclosing signature automatically. Directive edges are tagged source="directive" and survive incremental builds via a docname-keyed pending queue with an env-purge-doc handler.

From a registry YAML

For bulk declarative facts that live with the repo rather than the tests, drop a verification.yaml somewhere and point nexus_verification_registry at it:

version: 1

verifications:
  - test: py:function:tests.test_solver.test_attenuation
    verifies: [transport-cartesian]
    level: L0
    catches: [FM-07]

implementations:
  - function: py:function:orpheus.sn.solve_sn
    implements: [transport-cartesian]
    confidence: 1.0

Schema errors raise RegistryError at build time with a path-and-field context. Missing nodes (test / function / equation) are logged and skipped — the registry can name symbols that don't exist yet without breaking the build.

Querying the result

Every path above produces the same EdgeType.TESTS / EdgeType.IMPLEMENTS edges, so the audit tools don't care which source they came from. The source attribute distinguishes pytest.mark.verifies, directive, registry, and the fallback inferred heuristic.

Tier calibration caveat (#5): the declared tier is the precision instrument; the heuristic tiers are a best-effort safety net. When an equation's implements anchor lands on a low-level primitive (token overlap favors it), tests that exercise the equation through a user-facing driver get credited as heuristic-multihop rather than heuristic-1hop — the coverage is real, but the confidence label reads weaker than it is. Measured on a mature declared-tier project (ORPHEUS, 972 test-bearing entries): 2 equations (0.2%) show this signature. The remedy is an explicit @pytest.mark.verifies("label") on the driver tests, not heuristic tuning — if a multihop-only count surprises you, declare the link.

from sphinxcontrib.nexus.query import GraphQuery
from sphinxcontrib.nexus.export import load_sqlite

q = GraphQuery(load_sqlite("docs/_build/html/_nexus/graph.db"))

# Full audit bucketed by V&V level
audit = q.verification_audit(group_by="level", include_tests=True)
for level, gaps in audit.grouped.items():
    print(f"{level}: {len(gaps)} unverified equations")
print(f"declared: {audit.summary['tests_declared']}  heuristic: {audit.summary['tests_inferred']}")

# Gap hunt
gaps = q.verification_gaps(module="orpheus.sn", level="L0")
print(f"untagged tests in orpheus.sn: {len(gaps.untagged_tests)}")
print(f"unverified L0 equations:     {len(gaps.unverified_equations)}")

Same surface on the MCP side (verification_audit, verification_gaps) and the CLI (nexus audit, nexus gaps).

Git Worktrees & Workspaces

A graph database is a snapshot of one checkout. Agent harnesses (e.g. Claude Code) spawn the MCP server against the main checkout and keep it running when a session moves into a git worktree — so without help, worktree sessions silently query the wrong branch's graph. Nexus closes that hole in four layers:

1. Provenance stamping. Every graph write (Sphinx build, nexus analyze) stamps metadata["provenance"] with source_root, built_at, git_branch, git_commit, git_dirty. Every database says which tree it is a snapshot of.
2. Discovery. workspaces (MCP) / nexus workspaces (CLI) enumerate all checkouts via git worktree list and report which have graphs, on which branch, built from where.
3. Switching + tripwire. use_workspace(root) re-points the server at another checkout's graph (one server per agent session, so the switch is session-scoped); it accepts a worktree directory name, a branch name, or an absolute root path. session_briefing carries a workspace block that warns when the graph's branch no longer matches the checkout or when sibling worktrees have graphs of their own — the wrong-tree mismatch surfaces on the session's first turn.
4. Roots auto-alignment. session_briefing asks the client (MCP roots/list) which directory the session was launched from; when that lies inside a different checkout that has a graph, the server switches to it automatically and reports the switch under workspace.auto_align. Sessions launched inside a worktree need no manual step at all.

Recommended agent protocol for sessions that enter a worktree mid-session (roots updates there are client-dependent): build the docs (or run nexus analyze) inside the worktree, then call use_workspace(<worktree name>).

Storage

The graph is stored in two formats:

• SQLite (primary) — indexed queries, FTS5 full-text search, 0.05ms neighbor lookups. Written with a schema_version row in the metadata table. load_sqlite rejects databases written by a future nexus release with SchemaVersionError, so downgrading consumers fail loud instead of silently misreading.
• JSON (secondary) — human-readable, NetworkX node-link format.

Python API

from sphinxcontrib.nexus.export import load_sqlite
from sphinxcontrib.nexus.query import GraphQuery

kg = load_sqlite("_nexus/graph.db")
q = GraphQuery(kg)

# What uses numpy.ndarray?
q.query("ndarray", node_types=["external"])

# Blast radius of changing a function
q.impact("py:function:sn_solver.solve_sn", direction="upstream")

# Citation → equation → code chain
q.provenance_chain("py:function:sn_sweep.sweep_spherical")

# Migration plan
q.migration_plan("numpy", "jax")

License

MIT