MAINT Use tee to pipe stdout to build.log from buildpkg (#2293)

This makes it so that buildpkg generates build.log on its own
even when it isn't run from buildall. This is helpful because
when working on a specific package it is nicer to run buildpkg
directly so you can see the build on the console. However, it
is frustrating when you want to grep the build log for instance
that there isn't a build log.

This tees stdout into a build log from insidde buildpkg. It also
fixes the issue with overwriting build.log when nothing needs to
be done (though that issue I think was also fixed in December by
calling needs_build from buildall). Now buildall can just redirect
the subprocess output to /dev/null.

pyodide-build/pyodide_build/buildall.py

@@ -119,59 +119,42 @@ class Package(BasePackage):
 
     def build(self, outputdir: Path, args) -> None:
 
-        with open(self.pkgdir / "build.log.tmp", "w") as f:
-            p = subprocess.run(
-                [
-                    sys.executable,
-                    "-m",
-                    "pyodide_build",
-                    "buildpkg",
-                    str(self.pkgdir / "meta.yaml"),
-                    "--cflags",
-                    args.cflags,
-                    "--cxxflags",
-                    args.cxxflags,
-                    "--ldflags",
-                    args.ldflags,
-                    "--target-install-dir",
-                    args.target_install_dir,
-                    "--host-install-dir",
-                    args.host_install_dir,
-                    # Either this package has been updated and this doesn't
-                    # matter, or this package is dependent on a package that has
-                    # been updated and should be rebuilt even though its own
-                    # files haven't been updated.
-                    "--force-rebuild",
-                ],
-                check=False,
-                stdout=f,
-                stderr=subprocess.STDOUT,
+        p = subprocess.run(
+            [
+                sys.executable,
+                "-m",
+                "pyodide_build",
+                "buildpkg",
+                str(self.pkgdir / "meta.yaml"),
+                "--cflags",
+                args.cflags,
+                "--cxxflags",
+                args.cxxflags,
+                "--ldflags",
+                args.ldflags,
+                "--target-install-dir",
+                args.target_install_dir,
+                "--host-install-dir",
+                args.host_install_dir,
+                # Either this package has been updated and this doesn't
+                # matter, or this package is dependent on a package that has
+                # been updated and should be rebuilt even though its own
+                # files haven't been updated.
+                "--force-rebuild",
+            ],
+            check=False,
+            stdout=subprocess.DEVNULL,
+            stderr=subprocess.DEVNULL,
+        )
+
+        log_dir = Path(args.log_dir).resolve() if args.log_dir else None
+        if log_dir and (self.pkgdir / "build.log").exists():
+            log_dir.mkdir(exist_ok=True, parents=True)
+            shutil.copy(
+                self.pkgdir / "build.log",
+                log_dir / f"{self.name}.log",
             )
 
-        # Don't overwrite build log if we didn't build the file.
-        # If the file didn't need to be rebuilt, the log will have exactly two lines.
-        rebuilt = True
-        with open(self.pkgdir / "build.log.tmp") as f:
-            try:
-                next(f)
-                next(f)
-                next(f)
-            except StopIteration:
-                rebuilt = False
-
-        if rebuilt:
-            shutil.move(self.pkgdir / "build.log.tmp", self.pkgdir / "build.log")
-            log_dir = Path(args.log_dir).resolve() if args.log_dir else None
-
-            if log_dir and (self.pkgdir / "build.log").exists():
-                log_dir.mkdir(exist_ok=True, parents=True)
-                shutil.copy(
-                    self.pkgdir / "build.log",
-                    log_dir / f"{self.name}.log",
-                )
-        else:
-            (self.pkgdir / "build.log.tmp").unlink()
-
         if p.returncode != 0:
             print(f"Error building {self.name}. Printing build logs.")
 

pyodide-build/pyodide_build/buildpkg.py

@@ -678,6 +678,16 @@ def build_package(
             f"directory at the path {srcpath}, but that path does not exist."
         )
 
+    import os
+    import subprocess
+    import sys
+
+    tee = subprocess.Popen(["tee", pkg_root / "build.log"], stdin=subprocess.PIPE)
+    # Cause tee's stdin to get a copy of our stdin/stdout (as well as that
+    # of any child processes we spawn)
+    os.dup2(tee.stdin.fileno(), sys.stdout.fileno())  # type: ignore[union-attr]
+    os.dup2(tee.stdin.fileno(), sys.stderr.fileno())  # type: ignore[union-attr]
+
     with chdir(pkg_root), get_bash_runner() as bash_runner:
         bash_runner.env["PKG_VERSION"] = version
         if not continue_: