From fdc4ff034a198f92d14ca087bac4e0cf47613dee Mon Sep 17 00:00:00 2001
From: David Hagen <david@drhagen.com>
Date: Sat, 25 Apr 2026 07:53:14 -0400
Subject: [PATCH 1/5] Capture Rust code coverage

---
 .github/workflows/ci.yml |  33 +++++------
 .gitignore               |   3 +-
 docs/contributing.md     |  28 ++++++++-
 noxfile.py               | 121 +++++++++++++++++++++++++++++----------
 pyproject.toml           |   1 +
 rust-toolchain.toml      |   2 +-
 uv.lock                  |  26 +++++++++
 7 files changed, 163 insertions(+), 51 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 2a211da..08bd8e2 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -30,12 +30,10 @@ jobs:
     steps:
       - name: Checkout repo
         uses: actions/checkout@v4
-      - name: Build wheel
-        uses: PyO3/maturin-action@v1
+      - name: Install Rust toolchain
+        uses: actions-rust-lang/setup-rust-toolchain@v1
         with:
-          command: build
-          args: -o dist/ -i python${{ matrix.python }}
-          sccache: true
+          rustflags: ""
       - name: Install uv
         uses: astral-sh/setup-uv@v5
         with:
@@ -45,20 +43,18 @@ jobs:
       - name: Install dependencies
         run: uv sync --locked --only-group nox
       - name: Test
-        run: |
-          uv run --no-sync nox -s test-${{ matrix.python }} -- --use-dist
+        run: uv run --no-sync nox -s test-${{ matrix.python }}
       - name: Test Polars
-        run: |
-          uv run --no-sync nox -s test_polars-${{ matrix.python }} -- --use-dist
+        run: uv run --no-sync nox -s test_polars-${{ matrix.python }}
       - name: Test Pandas
-        run: |
-          uv run --no-sync nox -s test_pandas-${{ matrix.python }} -- --use-dist
+        run: uv run --no-sync nox -s test_pandas-${{ matrix.python }}
       - name: Store coverage
         uses: actions/upload-artifact@v4
         with:
           name: coverage-${{ matrix.platform }}-${{ matrix.python }}
-          path: .coverage.*
-          include-hidden-files: true
+          path: |
+            python.*.lcov
+            rust.*.lcov
           if-no-files-found: error
 
   coverage:
@@ -67,6 +63,8 @@ jobs:
     steps:
       - name: Checkout repo
         uses: actions/checkout@v4
+      - name: Install lcov
+        run: sudo apt-get update && sudo apt-get install -y lcov
       - name: Fetch coverage
         uses: actions/download-artifact@v4
         with:
@@ -80,12 +78,13 @@ jobs:
           cache-suffix: coverage
       - name: Install dependencies
         run: uv sync --locked --only-group nox
-      - name: Combine coverage and generate report
+      - name: Combine coverage
         run: uv run --no-sync nox -s coverage
       - name: Upload coverage to Codecov
         uses: codecov/codecov-action@v4
         with:
           token: ${{ secrets.CODECOV_TOKEN }}
+          files: combined.lcov
           fail_ci_if_error: true
 
   lint:
@@ -93,8 +92,10 @@ jobs:
     steps:
       - name: Checkout repo
         uses: actions/checkout@v4
-      - name: Setup sccache
-        uses: mozilla-actions/sccache-action@65101d47ea8028ed0c98a1cdea8dd9182e9b5133
+      - name: Install Rust toolchain
+        uses: actions-rust-lang/setup-rust-toolchain@v1
+        with:
+          cache-key: lint
       - name: Install uv
         uses: astral-sh/setup-uv@v5
         with:
diff --git a/.gitignore b/.gitignore
index d406832..e4f98a4 100644
--- a/.gitignore
+++ b/.gitignore
@@ -8,7 +8,8 @@ python/**/*.so
 
 # coverage
 /.coverage*
-/coverage.xml
+/*.lcov
+/htmlcov
 
 # mkdocs
 /site
diff --git a/docs/contributing.md b/docs/contributing.md
index 8f45480..623719b 100644
--- a/docs/contributing.md
+++ b/docs/contributing.md
@@ -20,13 +20,30 @@ git clone https://github.com/drhagen/tabeline.git
 
 ## Installing from source
 
-Tabeline uses uv as its packaging and dependency manager. In whatever Python environment you prefer, [install uv](https://docs.astral.sh/uv/getting-started/installation/) and then use uv to install Tabeline and its dependencies:
+Building Tabeline requires that a Rust compiler be available.
+In your environment, install [rustup](https://rustup.rs/) and then use it to install the appropriate rust version and rust-related tools:
+
+```shell
+rustup show
+```
+
+Tabeline uses uv as its Python packaging and dependency manager.
+In Python environment you prefer, [install uv](https://docs.astral.sh/uv/getting-started/installation/) and then use uv to install Tabeline and its dependencies:
 
 ```shell
-pip install uv
 uv sync
 ```
 
+Combining code coverage and generating a coverage report requires that `lcov` be installed.
+It is not available via rustup, cargo, or uv, so you'll have to install it from somewhere else:
+
+```shell
+pixi global install lcov
+sudo apt install lcov
+brew install lcov
+choco install lcov
+```
+
 ## Testing
 
 Tabeline uses pytest to run the tests in the `tests/` directory. The test command is encapsulated with Nox:
@@ -43,6 +60,13 @@ uv run nox -s test-3.13 test_pandas-3.13
 
 It is good to run the tests locally before making a PR, but it is not necessary to have all Python versions run. It is rare for a failure to appear in a single version, and the CI will catch it anyway.
 
+The tests generate code coverage data.
+To merge the coverage data and generate an HTML report at `htmlcov/`, run:
+
+```shell
+uv run nox -s coverage
+```
+
 ## Code quality
 
 Tabeline uses Ruff to ensure a minimum standard of code quality. The code quality commands are encapsulated with Nox:
diff --git a/noxfile.py b/noxfile.py
index 3b90c3d..20dade2 100644
--- a/noxfile.py
+++ b/noxfile.py
@@ -1,4 +1,6 @@
 import platform
+import subprocess
+from pathlib import Path
 
 from nox import Session, options, parametrize
 from nox_uv import session
@@ -7,25 +9,73 @@
 options.sessions = ["test", "test_polars", "test_pandas", "coverage", "lint"]
 
 
-def _install_project(s: Session):
-    # There is no way to cache the build of the project in CI without using the
-    # official Maturin action. So CI separately builds the dist/ wheel and then
-    # Nox installs the project from that wheel.
-    # Furthermore, uv does not build the project when using editable installs,
-    # so we have to explicitly build the project in editable mode by default.
-    if "--use-dist" in s.posargs:
-        s.run(
-            "uv",
-            "pip",
-            "install",
-            "--reinstall-package=tabeline",
-            "--no-index",
-            "--find-links=dist/",
-            "--no-deps",
-            "tabeline",
-        )
-    else:
-        s.run("uv", "pip", "install", "--no-deps", "--no-build", "-e", ".")
+def _run_tests(s: Session, test_name: str, *pytest_args: str):
+    # Almost all of this code is here to provide code coverage for the Rust
+    # code, which requires instrumentation and post-processing
+
+    # Set env so cargo-llvm-cov instruments the Rust build and writes profraw
+    # files to its expected target dir.
+    # This command spits out shell commmands to set variables, so they must be
+    # parsed, somewhat fragilly.
+    cov_env_output = subprocess.check_output(["cargo", "llvm-cov", "show-env"], text=True)
+    for line in cov_env_output.splitlines():
+        key, _, value = line.partition("=")
+        s.env[key] = value.strip().strip("'")
+
+    # Install Tabeline into the test virtual environment
+    # This may seem like a weird way to install the current project, but this is
+    # the only way to do it so that the Rust code actually builds and also does
+    # not interfere with other environments.
+    # Here are some simpler ways to build that do not work and why:
+    # 1. Do not build with `uv sync` because that is an editable build and that
+    #    won't build the Rust code.
+    # 2. Do not build with `uv sync --no-editable` because that won't rebuild
+    #    when the project is changed.
+    # 3. Do not build with `maturin develop --uv` because that will cause the
+    #    intrumentation to be left in dev environment causing raw coverage files
+    #    to be left in working directories every time Python is invoked.
+    s.run(
+        "uv",
+        "pip",
+        "install",
+        # Turn off build isolation so that we still get caching of Rust compiles
+        "--no-build-isolation",
+        # Force installation so that changes get installed
+        "--reinstall-package",
+        "tabeline",
+        # We already installed dependencies with nox-uv
+        "--no-deps",
+        # `uv pip install` triggers a maturin release build, which will put the
+        # instrumented binary in  target/release instead of target/debug where
+        # `cargo llvm-cov report` expects it
+        "--config-settings",
+        "build-args=--profile=dev",
+        ".",
+    )
+
+    coverage_data = f".coverage.{test_name}"
+
+    # Run the tests with coverage
+    s.run("coverage", "run", "--data-file", coverage_data, "-m", "pytest", *pytest_args)
+
+    # Convert the Python coverage data to the common lcov format
+    s.run("coverage", "lcov", "--data-file", coverage_data, "-o", f"python.{test_name}.lcov")
+    Path(coverage_data).unlink()
+
+    # Convert the Rust coverage data to the common lcov format
+    # This must be done here because the cargo-llvm-cov data is not portable
+    # (unlike the Python data)
+    s.run(
+        "cargo",
+        "llvm-cov",
+        "report",
+        "--lcov",
+        "--output-path",
+        f"rust.{test_name}.lcov",
+        "--ignore-filename-regex",
+        r"/\.cargo/|/rustc/",
+        external=True,
+    )
 
 
 @session(
@@ -34,9 +84,7 @@ def _install_project(s: Session):
     uv_no_install_project=True,
 )
 def test(s: Session):
-    _install_project(s)
-    coverage_file = f".coverage.{platform.machine()}.{platform.system()}.{s.python}"
-    s.run("coverage", "run", "--data-file", coverage_file, "-m", "pytest")
+    _run_tests(s, f"{platform.machine()}.{platform.system()}.{s.python}")
 
 
 @session(
@@ -46,9 +94,11 @@ def test(s: Session):
     uv_no_install_project=True,
 )
 def test_polars(s: Session):
-    _install_project(s)
-    coverage_file = f".coverage.{platform.machine()}.{platform.system()}.{s.python}.polars"
-    s.run("coverage", "run", "--data-file", coverage_file, "-m", "pytest", "tests/test_polars.py")
+    _run_tests(
+        s,
+        f"{platform.machine()}.{platform.system()}.{s.python}.polars",
+        "tests/test_polars.py",
+    )
 
 
 @session(
@@ -58,16 +108,25 @@ def test_polars(s: Session):
     uv_no_install_project=True,
 )
 def test_pandas(s: Session):
-    _install_project(s)
-    coverage_file = f".coverage.{platform.machine()}.{platform.system()}.{s.python}.pandas"
-    s.run("coverage", "run", "--data-file", coverage_file, "-m", "pytest", "tests/test_pandas.py")
+    _run_tests(
+        s,
+        f"{platform.machine()}.{platform.system()}.{s.python}.pandas",
+        "tests/test_pandas.py",
+    )
 
 
 @session(uv_only_groups=["test"])
 def coverage(s: Session):
-    s.run("coverage", "combine")
-    s.run("coverage", "html")
-    s.run("coverage", "xml")
+    lcovs = sorted(Path().glob("python.*.lcov")) + sorted(Path().glob("rust.*.lcov"))
+    add_args = [arg for p in lcovs for arg in ("-a", str(p))]
+    s.run("lcov", *add_args, "-o", "combined.lcov", external=True)
+    s.run(
+        "genhtml",
+        "combined.lcov",
+        "-o",
+        "htmlcov",
+        external=True,
+    )
 
 
 @session(uv_only_groups=["lint"])
diff --git a/pyproject.toml b/pyproject.toml
index 40239a3..91db311 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -56,6 +56,7 @@ nox = [
 ]
 
 test = [
+    "maturin == 1.*",
     "pytest == 9.*",
     "coverage",
 ]
diff --git a/rust-toolchain.toml b/rust-toolchain.toml
index 32c68ee..e498309 100644
--- a/rust-toolchain.toml
+++ b/rust-toolchain.toml
@@ -1,3 +1,3 @@
 [toolchain]
 channel = "1.94.1"
-components = ["rustfmt", "clippy"]
+components = ["rustfmt", "clippy", "llvm-tools-preview"]
diff --git a/uv.lock b/uv.lock
index 8d81fab..758087e 100644
--- a/uv.lock
+++ b/uv.lock
@@ -500,6 +500,30 @@ wheels = [
     { url = "https://files.pythonhosted.org/packages/70/bc/6f1c2f612465f5fa89b95bead1f44dcb607670fd42891d8fdcd5d039f4f4/markupsafe-3.0.3-cp314-cp314t-win_arm64.whl", hash = "sha256:32001d6a8fc98c8cb5c947787c5d08b0a50663d139f1305bac5885d98d9b40fa", size = 14146, upload-time = "2025-09-27T18:37:28.327Z" },
 ]
 
+[[package]]
+name = "maturin"
+version = "1.13.1"
+source = { registry = "https://pypi.org/simple" }
+dependencies = [
+    { name = "tomli", marker = "python_full_version < '3.11'" },
+]
+sdist = { url = "https://files.pythonhosted.org/packages/39/16/b284a7bc4af3dd87717c784278c1b8cb18606ad1f6f7a671c47bfd9c3df0/maturin-1.13.1.tar.gz", hash = "sha256:9a87ff3b8e4d1c6eac33ebfe8e261e8236516d98d45c0323550621819b5a1a2f", size = 340369, upload-time = "2026-04-09T15:14:07.026Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/43/4d/a23fc95be881aa8c7a6ea353410417872e4d7065df03d7f3db8f0dbed4a7/maturin-1.13.1-py3-none-linux_armv6l.whl", hash = "sha256:416e4e01cb88b798e606ee43929df897e42c1647b722ef68283816cca99a8742", size = 10102444, upload-time = "2026-04-09T15:13:48.393Z" },
+    { url = "https://files.pythonhosted.org/packages/a6/1e/65c385d65bae95cf04895d52f39dbed8b1453ae55da2903d252ade40a774/maturin-1.13.1-py3-none-macosx_10_12_x86_64.macosx_11_0_arm64.macosx_10_12_universal2.whl", hash = "sha256:72888e87819ce546d0d2df900e4b385e4ef299077d92ee37b48923a5602dae94", size = 19576043, upload-time = "2026-04-09T15:14:08.685Z" },
+    { url = "https://files.pythonhosted.org/packages/8f/13/f6bc868d0bfecd9314870b97f530a167e31f7878ac4945c78245c6eef69c/maturin-1.13.1-py3-none-macosx_10_12_x86_64.whl", hash = "sha256:98b5fcf1a186c217830a8295ecc2989c6b1cf50945417adfc15252107b9475b7", size = 10117339, upload-time = "2026-04-09T15:13:40.559Z" },
+    { url = "https://files.pythonhosted.org/packages/51/58/279e081305c11c1c1c4fccacf77df8959646c5d4de7a57ec7e787653e270/maturin-1.13.1-py3-none-manylinux_2_12_i686.manylinux2010_i686.musllinux_1_1_i686.whl", hash = "sha256:3da18cccf2f683c0977bff9146a0908d6ffce836d600665736ac01679f588cb9", size = 10139689, upload-time = "2026-04-09T15:13:38.291Z" },
+    { url = "https://files.pythonhosted.org/packages/00/94/69391af5396c6aab723932240803f49e5f3de3dd7c57d32f02d237a0ce32/maturin-1.13.1-py3-none-manylinux_2_12_x86_64.manylinux2010_x86_64.musllinux_1_1_x86_64.whl", hash = "sha256:6b1e5916a253243e8f5f9e847b62bbc98420eec48c9ce2e2e8724c6da89d359b", size = 10551141, upload-time = "2026-04-09T15:13:42.887Z" },
+    { url = "https://files.pythonhosted.org/packages/9e/bf/4edac2667b49e3733438062ae416413b8fc8d42e1bd499ba15e1fb02fc55/maturin-1.13.1-py3-none-manylinux_2_17_aarch64.manylinux2014_aarch64.musllinux_1_1_aarch64.whl", hash = "sha256:dc91031e0619c1e28730279ef9ee5f106c9b9ec806b013f888676b242f892eb7", size = 9983094, upload-time = "2026-04-09T15:13:56.868Z" },
+    { url = "https://files.pythonhosted.org/packages/79/94/a6d651cfe8fc6bf2e892c90e3cdbb25c06d81c9115140d03ea1a68a97575/maturin-1.13.1-py3-none-manylinux_2_17_armv7l.manylinux2014_armv7l.musllinux_1_1_armv7l.whl", hash = "sha256:001741c6cff56aa8ea59a0d78ae990c0550d0e3e82b00b683eedb4158a8ef7e6", size = 9949980, upload-time = "2026-04-09T15:13:59.185Z" },
+    { url = "https://files.pythonhosted.org/packages/b5/d1/82c067464f848e38af9910bce55eb54302b1c1284a279d515dbfcf5994f5/maturin-1.13.1-py3-none-manylinux_2_17_ppc64le.manylinux2014_ppc64le.musllinux_1_1_ppc64le.whl", hash = "sha256:01c845825c917c07c1d0b2c9032c59c16a7d383d1e649a46481d3e5693c2750f", size = 13186276, upload-time = "2026-04-09T15:13:45.725Z" },
+    { url = "https://files.pythonhosted.org/packages/7c/f4/25367baf1025580f047f9b37598bb3fadc416e24536afd4f28e190335c73/maturin-1.13.1-py3-none-manylinux_2_17_s390x.manylinux2014_s390x.whl", hash = "sha256:f69093ed4a0e6464e52a7fc26d714f859ce15630ec8070743398c6bf41f38a9e", size = 10891837, upload-time = "2026-04-09T15:13:35.68Z" },
+    { url = "https://files.pythonhosted.org/packages/af/be/caafad8ce74974b7deafdf144d12f758993dfea4c66c9905b138f51a7792/maturin-1.13.1-py3-none-manylinux_2_31_riscv64.musllinux_1_1_riscv64.whl", hash = "sha256:c1490584f3c70af45466ee99065b49e6657ebdccac6b10571bb44681309c9396", size = 10351032, upload-time = "2026-04-09T15:14:01.632Z" },
+    { url = "https://files.pythonhosted.org/packages/66/0e/970a721d27cfa410e8bfa0a1e32e6ef52cb8169692110a5fdabe1af3f570/maturin-1.13.1-py3-none-win32.whl", hash = "sha256:c6a720b252c99de072922dbe4432ab19662b6f80045b0355fec23bdfccb450da", size = 8855465, upload-time = "2026-04-09T15:13:51.122Z" },
+    { url = "https://files.pythonhosted.org/packages/88/70/7c1e0d65fa147d5479055a171541c82b8cdfc1c825d85a82240470f14176/maturin-1.13.1-py3-none-win_amd64.whl", hash = "sha256:a2017d2281203d0c6570240e7d746564d766d756105823b7de68bda6ae722711", size = 10230471, upload-time = "2026-04-09T15:13:53.89Z" },
+    { url = "https://files.pythonhosted.org/packages/c5/2a/afe0193b673a79ffd2e01ad999511b7e9e6b49af02bb3759d82a78c3043d/maturin-1.13.1-py3-none-win_arm64.whl", hash = "sha256:2839024dcd65776abb4759e5bca29941971e095574162a4d335191da4be9ff24", size = 8905575, upload-time = "2026-04-09T15:14:03.891Z" },
+]
+
 [[package]]
 name = "mergedeep"
 version = "1.3.4"
@@ -1278,6 +1302,7 @@ nox = [
 ]
 test = [
     { name = "coverage" },
+    { name = "maturin" },
     { name = "pytest" },
 ]
 
@@ -1298,6 +1323,7 @@ lint = [{ name = "ruff", specifier = "==0.15.*" }]
 nox = [{ name = "nox-uv", specifier = "==0.7.*" }]
 test = [
     { name = "coverage" },
+    { name = "maturin", specifier = "==1.*" },
     { name = "pytest", specifier = "==9.*" },
 ]
 

From 54a7d4656f6ef54cfc3b50f48887050d1f742fc2 Mon Sep 17 00:00:00 2001
From: David Hagen <david@drhagen.com>
Date: Sat, 25 Apr 2026 09:43:37 -0400
Subject: [PATCH 2/5] Install cargo-llvm-cov on CI

---
 .github/workflows/ci.yml | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 08bd8e2..5f53b73 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -34,6 +34,8 @@ jobs:
         uses: actions-rust-lang/setup-rust-toolchain@v1
         with:
           rustflags: ""
+      - name: Install cargo-llvm-cov
+        uses: taiki-e/install-action@cargo-llvm-cov
       - name: Install uv
         uses: astral-sh/setup-uv@v5
         with:

From 808b7c5be80c246bc816ac867b00c74f30a0b98e Mon Sep 17 00:00:00 2001
From: David Hagen <david@drhagen.com>
Date: Sat, 25 Apr 2026 14:45:23 -0400
Subject: [PATCH 3/5] Try to use relative paths

---
 noxfile.py     | 24 ++++++++++++++++++++----
 pyproject.toml |  4 ++++
 2 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/noxfile.py b/noxfile.py
index 20dade2..b8497ad 100644
--- a/noxfile.py
+++ b/noxfile.py
@@ -17,7 +17,13 @@ def _run_tests(s: Session, test_name: str, *pytest_args: str):
     # files to its expected target dir.
     # This command spits out shell commmands to set variables, so they must be
     # parsed, somewhat fragilly.
-    cov_env_output = subprocess.check_output(["cargo", "llvm-cov", "show-env"], text=True)
+    # --remap-path-prefix injects rustc's --remap-path-prefix=$workspace= flag
+    # into the build, so SF: paths in the resulting lcov are repo-relative and
+    # therefore portable across OS runners. The matching flag is also passed
+    # to `cargo llvm-cov report` below.
+    cov_env_output = subprocess.check_output(
+        ["cargo", "llvm-cov", "show-env", "--remap-path-prefix"], text=True
+    )
     for line in cov_env_output.splitlines():
         key, _, value = line.partition("=")
         s.env[key] = value.strip().strip("'")
@@ -58,13 +64,22 @@ def _run_tests(s: Session, test_name: str, *pytest_args: str):
     # Run the tests with coverage
     s.run("coverage", "run", "--data-file", coverage_data, "-m", "pytest", *pytest_args)
 
+    # Combine the data file into itself to apply [tool.coverage.paths] aliasing,
+    # which remaps the nox-installed site-packages location back to the source
+    # tree (e.g. .nox/.../site-packages/tabeline/ -> python/tabeline/). Without
+    # this step `coverage lcov` would emit the literal recorded path, which
+    # varies per OS and Python version and breaks cross-runner combining.
+    combined_data = f"{coverage_data}.combined"
+    s.run("coverage", "combine", "--data-file", combined_data, coverage_data)
+
     # Convert the Python coverage data to the common lcov format
-    s.run("coverage", "lcov", "--data-file", coverage_data, "-o", f"python.{test_name}.lcov")
-    Path(coverage_data).unlink()
+    s.run("coverage", "lcov", "--data-file", combined_data, "-o", f"python.{test_name}.lcov")
+    Path(combined_data).unlink()
 
     # Convert the Rust coverage data to the common lcov format
     # This must be done here because the cargo-llvm-cov data is not portable
-    # (unlike the Python data)
+    # (unlike the Python data). --remap-path-prefix strips the workspace root
+    # from SF: paths so the lcov is portable across OS runners.
     s.run(
         "cargo",
         "llvm-cov",
@@ -74,6 +89,7 @@ def _run_tests(s: Session, test_name: str, *pytest_args: str):
         f"rust.{test_name}.lcov",
         "--ignore-filename-regex",
         r"/\.cargo/|/rustc/",
+        "--remap-path-prefix",
         external=True,
     )
 
diff --git a/pyproject.toml b/pyproject.toml
index 91db311..e20a07b 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -86,6 +86,10 @@ filterwarnings = ["error"]
 [tool.coverage.run]
 branch = true
 source = ["tabeline"]
+# Record relative paths so coverage data combines cleanly across OS runners
+# and so [tool.coverage.paths] aliasing maps the nox-installed site-packages
+# location back to the source tree.
+relative_files = true
 
 [tool.coverage.report]
 exclude_lines = [

From 2df973fb2dde7a42b4117c7d55294b6f2cac684a Mon Sep 17 00:00:00 2001
From: David Hagen <david@drhagen.com>
Date: Sat, 25 Apr 2026 21:10:44 -0400
Subject: [PATCH 4/5] Rewrite Windows paths

---
 noxfile.py | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/noxfile.py b/noxfile.py
index b8497ad..4b4b5a3 100644
--- a/noxfile.py
+++ b/noxfile.py
@@ -80,19 +80,32 @@ def _run_tests(s: Session, test_name: str, *pytest_args: str):
     # This must be done here because the cargo-llvm-cov data is not portable
     # (unlike the Python data). --remap-path-prefix strips the workspace root
     # from SF: paths so the lcov is portable across OS runners.
+    rust_lcov = Path(f"rust.{test_name}.lcov")
     s.run(
         "cargo",
         "llvm-cov",
         "report",
         "--lcov",
         "--output-path",
-        f"rust.{test_name}.lcov",
+        str(rust_lcov),
         "--ignore-filename-regex",
         r"/\.cargo/|/rustc/",
         "--remap-path-prefix",
         external=True,
     )
 
+    # On Windows, cargo-llvm-cov writes SF: paths with backslashes, which break
+    # genhtml when the lcov is later merged on Linux (backslashes get treated
+    # as literal filename characters). Neither cargo-llvm-cov nor llvm-cov has
+    # a flag to force forward slashes, so rewrite SF: lines in place.
+    rust_lcov.write_text(
+        "\n".join(
+            "SF:" + line[3:].replace("\\", "/") if line.startswith("SF:") else line
+            for line in rust_lcov.read_text().splitlines()
+        )
+        + "\n"
+    )
+
 
 @session(
     python=["3.10", "3.11", "3.12", "3.13", "3.14"],

From 04c7e03e7d0192e3cfeef73edeb21e53b8df5a3d Mon Sep 17 00:00:00 2001
From: David Hagen <david@drhagen.com>
Date: Sun, 26 Apr 2026 21:57:45 -0400
Subject: [PATCH 5/5] Normalize Windows line endings for Python too

---
 noxfile.py | 30 ++++++++++++++++++------------
 1 file changed, 18 insertions(+), 12 deletions(-)

diff --git a/noxfile.py b/noxfile.py
index 4b4b5a3..fb6114d 100644
--- a/noxfile.py
+++ b/noxfile.py
@@ -9,6 +9,20 @@
 options.sessions = ["test", "test_polars", "test_pandas", "coverage", "lint"]
 
 
+def _normalize_lcov_separators(lcov: Path) -> None:
+    # On Windows, both coverage.py and cargo-llvm-cov write SF: paths with
+    # backslashes, which break genhtml when the lcov is later merged on Linux
+    # (backslashes get treated as literal filename characters). Neither tool
+    # has a flag to force forward slashes, so rewrite SF: lines in place.
+    lcov.write_text(
+        "\n".join(
+            "SF:" + line[3:].replace("\\", "/") if line.startswith("SF:") else line
+            for line in lcov.read_text().splitlines()
+        )
+        + "\n"
+    )
+
+
 def _run_tests(s: Session, test_name: str, *pytest_args: str):
     # Almost all of this code is here to provide code coverage for the Rust
     # code, which requires instrumentation and post-processing
@@ -73,8 +87,10 @@ def _run_tests(s: Session, test_name: str, *pytest_args: str):
     s.run("coverage", "combine", "--data-file", combined_data, coverage_data)
 
     # Convert the Python coverage data to the common lcov format
-    s.run("coverage", "lcov", "--data-file", combined_data, "-o", f"python.{test_name}.lcov")
+    python_lcov = Path(f"python.{test_name}.lcov")
+    s.run("coverage", "lcov", "--data-file", combined_data, "-o", str(python_lcov))
     Path(combined_data).unlink()
+    _normalize_lcov_separators(python_lcov)
 
     # Convert the Rust coverage data to the common lcov format
     # This must be done here because the cargo-llvm-cov data is not portable
@@ -94,17 +110,7 @@ def _run_tests(s: Session, test_name: str, *pytest_args: str):
         external=True,
     )
 
-    # On Windows, cargo-llvm-cov writes SF: paths with backslashes, which break
-    # genhtml when the lcov is later merged on Linux (backslashes get treated
-    # as literal filename characters). Neither cargo-llvm-cov nor llvm-cov has
-    # a flag to force forward slashes, so rewrite SF: lines in place.
-    rust_lcov.write_text(
-        "\n".join(
-            "SF:" + line[3:].replace("\\", "/") if line.startswith("SF:") else line
-            for line in rust_lcov.read_text().splitlines()
-        )
-        + "\n"
-    )
+    _normalize_lcov_separators(rust_lcov)
 
 
 @session(