Set the basepath for PR previews

.github/workflows/pr-preview.yml

@@ -44,7 +44,11 @@ jobs:
           ref: ${{ github.event.pull_request.head.ref }}
 
       - name: Build static site
-        run: scripts/pr_previews/builder.py ${{ env.PR_PREVIEW_PATH }} --proof-of-concept
+        run: >
+          scripts/pr_previews/builder.py
+          ${{ env.PR_PREVIEW_PATH }}
+          --basepath /documentation/${{ env.PR_PREVIEW_PATH }} 
+          --proof-of-concept
 
       - name: Deploy to GitHub Pages
         run: scripts/pr_previews/deploy.py ${{ env.PR_PREVIEW_PATH }}

scripts/pr_previews/builder.py

@@ -15,6 +15,7 @@
 from __future__ import annotations
 
 import logging
+import os
 import shutil
 from argparse import ArgumentParser
 from contextlib import contextmanager
@@ -32,6 +33,11 @@
 def create_parser() -> ArgumentParser:
     parser = ArgumentParser()
     parser.add_argument("dest", help="The output folder", type=Path)
+    parser.add_argument(
+        "--basepath",
+        help="The subfolder for relative links, like `/documentation/pr-x`",
+        required=True,
+    )
     parser.add_argument(
         "--proof-of-concept",
         help="Build a simple index.html, rather than actual docs app.",
@@ -47,7 +53,7 @@ def main() -> None:
         return
 
     with setup_dir() as dir:
-        yarn_build(dir)
+        yarn_build(dir, args.basepath)
         save_output(dir, args.dest)
 
 
@@ -71,15 +77,22 @@ def write_proof_of_concept(dest: Path) -> None:
     logger.info(f"Wrote proof-of-concept index.html to {dest}")
 
 
-def yarn_build(root_dir: Path) -> None:
+def yarn_build(root_dir: Path, base_path: str) -> None:
     # This ensures that dependencies like Sharp are properly installed. Most
     # dependencies, like the first-party deps, will already have been installed.
     run_subprocess(["yarn", "install"], cwd=root_dir, stream_output=True)
-    run_subprocess(["yarn", "build"], cwd=root_dir, stream_output=True)
+    run_subprocess(
+        ["yarn", "build"],
+        cwd=root_dir,
+        env={**os.environ, "NEXT_PUBLIC_BASE_PATH": base_path},
+        stream_output=True,
+    )
 
 
 def save_output(root_dir: Path, dest: Path) -> None:
-    dest.mkdir(parents=True, exist_ok=True)
+    if dest.exists():
+        shutil.rmtree(dest)
+    dest.mkdir(parents=True)
     for item in (root_dir / "packages/preview/out").iterdir():
         if item.is_dir():
             shutil.copytree(item, dest / item.name)

scripts/pr_previews/utils.py

@@ -32,6 +32,7 @@ def run_subprocess(
     cmd: list[str],
     *,
     cwd: Path | None = None,
+    env: dict[str, str] | None = None,
     stream_output: bool = False,
 ) -> subprocess.CompletedProcess:
     output_dest = None if stream_output else subprocess.PIPE
@@ -40,6 +41,7 @@ def run_subprocess(
     result = subprocess.run(
         cmd,
         cwd=cwd,
+        env=env,
         stdout=output_dest,
         stderr=output_dest,
         text=True,