Fix RTD docs build failure by skipping Rust/maturin compilation

The PR #146 change to build from source triggers maturin, which compiles
the full Rust backend (faer, pyo3, rayon) with LTO — exceeding RTD's
build limits. The Rust backend is unnecessary for docs.

- Remove Rust toolchain and pip install from .readthedocs.yaml
- Install only runtime + docs deps via post_install hook
- Add sys.path insert in docs/conf.py so autodoc imports from source

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: igerber

.readthedocs.yaml

@@ -7,18 +7,17 @@ build:
   os: ubuntu-22.04
   tools:
     python: "3.11"
-    # Rust needed for maturin build. Pin for cache stability; update periodically.
-    rust: "1.82"
+  jobs:
+    post_install:
+      # Install runtime + docs deps without building the package itself.
+      # The Rust backend is optional and unnecessary for docs, so we skip
+      # the maturin build entirely. Sphinx imports diff_diff from the
+      # checked-out source via sys.path (see docs/conf.py).
+      #
+      # Keep in sync with pyproject.toml [project.dependencies]
+      # and [project.optional-dependencies.docs].
+      - pip install "numpy>=1.20.0" "pandas>=1.3.0" "scipy>=1.7.0" "sphinx>=6.0" "sphinx-rtd-theme>=1.0"
 
 # Build documentation in the "docs/" directory with Sphinx
 sphinx:
   configuration: docs/conf.py
-
-# Install from checked-out source so autodoc always matches the code at this ref.
-# Dependencies consolidated in pyproject.toml [project.optional-dependencies.docs].
-python:
-  install:
-    - method: pip
-      path: .
-      extra_requirements:
-        - docs

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 - Fix docs/PyPI version mismatch (issue #146) — RTD now builds versioned docs from source
+- Fix RTD docs build failure caused by Rust/maturin compilation timeout on ReadTheDocs
 
 ### Changed
 - Remove Rust outer-loop variance estimation for SyntheticDiD (placebo and bootstrap)

docs/conf.py

@@ -4,6 +4,14 @@
 # https://www.sphinx-doc.org/en/master/usage/configuration.html
 
 import os
+import sys
+
+# Add repository root to sys.path so autodoc imports from checked-out source
+# without needing pip install (which would require the Rust/maturin toolchain).
+# Note: visualization.py lazily imports matplotlib inside functions, so it is
+# not needed as a build dependency. If a future module adds a top-level
+# matplotlib import, add it to the RTD dep list in .readthedocs.yaml.
+sys.path.insert(0, os.path.abspath(".."))
 
 import diff_diff