Uses thin ar static libraries.

We are crossing the 100 MB hard limit on GitHub file sizes.

Two alternatives:

1) Make split archives, and change the LDFLAGS to include all of them.
2) Make split archives, and then make an empty parent archive that sets additional linker flags using "ar l".
   This would avoid having to update Go files, but wide compatibility is less certain.

We can't use GitHub Large Files Support, since go get wouldn't see the files.

For Windows, it's not clear what we'd have to do.

.github/workflows/v8build.yml

@@ -127,7 +127,9 @@ jobs:
                   # The name matches the directory under deps/.
                   name: ${{ matrix.os }}_${{ matrix.arch }}
                   if-no-files-found: error
-                  path: deps/${{ matrix.os }}_${{ matrix.arch }}/libv8.a
+                  path: |
+                      deps/${{ matrix.os }}_${{ matrix.arch }}/libv8.a
+                      deps/${{ matrix.os }}_${{ matrix.arch }}/obj/
                   retention-days: 2
 
     commit:

deps/build.py

@@ -1,9 +1,10 @@
 #!/usr/bin/env python3
-import platform
+import argparse
+import glob
 import os
-import subprocess
+import platform
 import shutil
-import argparse
+import subprocess
 
 valid_archs = ['arm64', 'x86_64']
 # "x86_64" is called "amd64" on Windows
@@ -93,6 +94,36 @@ def v8deps():
                         cwd=deps_path,
                         env=env)
 
+def build_gn_args():
+    is_debug = args.debug
+    is_clang = args.clang if args.clang is not None else args.os != "linux"
+    arch = v8_arch()
+    # symbol_level = 1 includes line number information
+    # symbol_level = 2 can be used for additional debug information, but it can increase the
+    #   compiled library by an order of magnitude and further slow down compilation
+    symbol_level = 1 if args.debug else 0
+    strip_debug_info = not args.debug
+
+    gnargs = gn_args % (
+        str(bool(is_debug)).lower(),
+        str(is_clang).lower(),
+        v8_os(),
+        arch,
+        arch,
+        symbol_level,
+        str(strip_debug_info).lower(),
+    )
+    if args.ccache:
+        gnargs += 'cc_wrapper="ccache"\n'
+    if not is_clang and arch == "arm64":
+        # https://chromium.googlesource.com/chromium/deps/icu/+/2958a507f15e475045906d73af39018d5038a93b
+        # introduced -mmark-bti-property, which isn't supported by GCC.
+        #
+        # V8 itself fixed this in https://chromium-review.googlesource.com/c/v8/v8/+/3930160.
+        gnargs += 'arm_control_flow_integrity="none"\n'
+
+    return gnargs
+
 def cmd(args):
     return ["cmd", "/c"] + args if is_windows else args
 
@@ -125,6 +156,42 @@ def update_last_change():
     out_path = os.path.join(v8_path, "build", "util", "LASTCHANGE")
     subprocess.check_call(["python", "build/util/lastchange.py", "-o", out_path], cwd=v8_path)
 
+def convert_to_thin_ar(src_fn, dest_fn, dest_obj_dn):
+    """Extracts all files from src_fn to dest_obj_dn/ and makes a thin archive at dest_fn.
+
+    GitHub's file size limit is 100 MiB, and the archive is hitting that.
+    """
+    dest_path = os.path.dirname(dest_fn)
+
+    ar_path = "ar"
+    if args.os == "linux" and args.arch == "arm64":
+        ar_path = "aarch64-linux-gnu-ar"
+
+    if os.path.exists(dest_obj_dn):
+        shutil.rmtree(dest_obj_dn)
+    os.makedirs(dest_obj_dn)
+
+    subprocess.check_call(
+        [
+            ar_path,
+            "x",
+            "--output", dest_obj_dn,
+            src_fn,
+        ],
+        cwd=v8_path)
+
+    if os.path.exists(dest_fn):
+        os.unlink(dest_fn)
+
+    subprocess.check_call(
+        [
+            ar_path,
+            "qsc",
+            "--thin",
+            dest_fn,
+        ] + [os.path.relpath(fn, dest_path) for fn in glob.glob(os.path.join(dest_obj_dn, "*"))],
+        cwd=dest_path)
+
 def main():
     v8deps()
     if is_windows:
@@ -136,48 +203,17 @@ def main():
     assert(os.path.exists(ninja_path))
 
     build_path = os.path.join(deps_path, ".build", os_arch())
-    env = os.environ.copy()
-
-    is_debug = args.debug
-    is_clang = args.clang if args.clang is not None else args.os != "linux"
-    arch = v8_arch()
-    # symbol_level = 1 includes line number information
-    # symbol_level = 2 can be used for additional debug information, but it can increase the
-    #   compiled library by an order of magnitude and further slow down compilation
-    symbol_level = 1 if args.debug else 0
-    strip_debug_info = not args.debug
 
-    gnargs = gn_args % (
-        str(bool(is_debug)).lower(),
-        str(is_clang).lower(),
-        v8_os(),
-        arch,
-        arch,
-        symbol_level,
-        str(strip_debug_info).lower(),
-    )
-    if args.ccache:
-        gnargs += 'cc_wrapper="ccache"\n'
-    if not is_clang and arch == "arm64":
-        # https://chromium.googlesource.com/chromium/deps/icu/+/2958a507f15e475045906d73af39018d5038a93b
-        # introduced -mmark-bti-property, which isn't supported by GCC.
-        #
-        # V8 itself fixed this in https://chromium-review.googlesource.com/c/v8/v8/+/3930160.
-        gnargs += 'arm_control_flow_integrity="none"\n'
+    gnargs = build_gn_args()
 
-    subprocess.check_call(cmd([gn_path, "gen", build_path, "--args=" + gnargs.replace('\n', ' ')]),
-                        cwd=v8_path,
-                        env=env)
-    subprocess.check_call([ninja_path, "-v", "-C", build_path, "v8_monolith"],
-                        cwd=v8_path,
-                        env=env)
+    subprocess.check_call(cmd([gn_path, "gen", build_path, "--args=" + gnargs.replace('\n', ' ')]), cwd=v8_path)
+    subprocess.check_call([ninja_path, "-v", "-C", build_path, "v8_monolith"], cwd=v8_path)
 
-    lib_fn = os.path.join(build_path, "obj/libv8_monolith.a")
     dest_path = os.path.join(deps_path, os_arch())
-    if not os.path.exists(dest_path):
-        os.makedirs(dest_path)
-    dest_fn = os.path.join(dest_path, 'libv8.a')
-    shutil.copy(lib_fn, dest_fn)
+    convert_to_thin_ar(
+        os.path.join(build_path, "obj/libv8_monolith.a"),
+        os.path.join(dest_path, "libv8.a"),
+        os.path.join(dest_path, "obj"))
 
 
 if __name__ == "__main__":