Fix up

Author: fmeum

go/private/extensions.bzl

@@ -198,8 +198,34 @@ def _go_sdk_impl(ctx):
     host_detected_goos, host_detected_goarch = detect_host_platform(ctx)
     toolchains = []
 
-    sdks_by_version = getattr(ctx, "facts", None) or {}
-    used_versions = {}
+    all_sdks_by_version = {}
+    used_sdks_by_version = {}
+    facts = getattr(ctx, "facts", {})
+
+    def get_sdks_by_version_cached(version):
+        # Avoid a download without a known digest in the SDK repo rule by fetching the SDKs filename
+        # and digest here. When using a version of Bazel that supports module extension facts, this
+        # info will be persisted in the lockfile, allowing for truly airgapped builds with an
+        # up-to-date lockfile and download (formerly repository) cache.
+        sdks = facts.get(version)
+        if sdks == None:
+            # Lazily fetch the information about all SDKs so that we avoid the download if the facts
+            # already contain all the versions we care about. We take care to only do this once and
+            # also accept failures to support airgapped builds: the user may have set sdk hashes on
+            # all SDK repos they actually intend to use, but others (e.g., the default SDK added by
+            # rules_go) trigger this path even if they would never be selected by toolchain
+            # resolution. We must not break those builds.
+            if not all_sdks_by_version:
+                all_sdks_by_version.clear()
+                all_sdks_by_version.update(fetch_sdks_by_version(ctx, allow_fail = True))
+            sdks = all_sdks_by_version.get(version)
+        if sdks == None:
+            # This is either caused by an invalid version or because we are in an airgapped build
+            # and the version wasn't present in facts. Since we don't want to fail in the latter
+            # case, we leave it to the repository rule to report a useful error message.
+            return None
+        used_sdks_by_version[version] = sdks
+        return sdks
 
     for module in ctx.modules:
         # Apply wrapped toolchains first to override specific platforms from the
@@ -266,9 +292,7 @@ def _go_sdk_impl(ctx):
             )
 
             _download_sdk(
-                module_ctx = ctx,
-                sdks_by_version = sdks_by_version,
-                used_versions = used_versions,
+                get_sdks_by_version = get_sdks_by_version_cached,
                 name = name,
                 goos = download_tag.goos,
                 goarch = download_tag.goarch,
@@ -307,9 +331,7 @@ def _go_sdk_impl(ctx):
                     )
 
                     _download_sdk(
-                        module_ctx = ctx,
-                        sdks_by_version = sdks_by_version,
-                        used_versions = used_versions,
+                        get_sdks_by_version = get_sdks_by_version_cached,
                         name = default_name,
                         goos = goos,
                         goarch = goarch,
@@ -381,11 +403,7 @@ def _go_sdk_impl(ctx):
 
         # See _download_sdk below for details on these facts.
         if hasattr(ctx, "facts"):
-            kwargs["facts"] = {
-                version: sdk_info
-                for version, sdk_info in sdks_by_version.items()
-                if version in used_versions
-            }
+            kwargs["facts"] = used_sdks_by_version
         return ctx.extension_metadata(**kwargs)
     else:
         return None
@@ -416,23 +434,11 @@ def _left_pad_zero(index, length):
         fail("index must be non-negative")
     return ("0" * length + str(index))[-length:]
 
-def _download_sdk(*, module_ctx, sdks_by_version, used_versions, name, goos, goarch, download_tag):
+def _download_sdk(*, get_sdks_by_version, name, goos, goarch, download_tag):
     version = download_tag.version
     sdks = download_tag.sdks
     if version and not sdks:
-        # Avoid a download without a known digest in the SDK repo rule by fetching the SDKs filename
-        # and digest here. When using a version of Bazel that supports module extension facts, this
-        # info will be persisted in the lockfile, allowing for truly airgapped builds with an
-        # up-to-date lockfile and download (formerly repository) cache.
-        if version not in sdks_by_version:
-            # Lazily fetch the information about all SDKs so that we avoid the download if the facts
-            # already contain all the versions we care about.
-            sdks_by_version.clear()
-            sdks_by_version.update(fetch_sdks_by_version(module_ctx))
-        if version not in sdks_by_version:
-            fail("go_sdk: no SDKs found for version {} requested by".format(version), download_tag)
-        used_versions[version] = True
-        sdks = sdks_by_version[version]
+        sdks = get_sdks_by_version(version)
 
     go_download_sdk_rule(
         name = name,

go/private/sdk.bzl

@@ -570,16 +570,26 @@ def _parse_versions_json(data):
         for sdk in sdks
     }
 
-def fetch_sdks_by_version(ctx):
-    ctx.download(
+def fetch_sdks_by_version(ctx, allow_fail = False):
+    result = ctx.download(
         url = [
             "https://go.dev/dl/?mode=json&include=all",
             "https://golang.google.cn/dl/?mode=json&include=all",
         ],
         output = "versions.json",
+        allow_fail = allow_fail,
     )
+    if not result.success:
+        return {}
     data = ctx.read("versions.json")
 
+    # If the download is redirected through a proxy such as Artifactory, it may
+    # drop the query parameters and return an HTML page instead. In that case,
+    # just return an empty map if allow_fail is set. It is unfortunately not
+    # possible to attempt parsing as JSON and catch the error.
+    if (not data or data[0] != "[") and allow_fail:
+        return {}
+
     # module_ctx doesn't have delete, but its files are temporary anyway.
     if hasattr(ctx, "delete"):
         ctx.delete("versions.json")

tests/bcr/.bazelversion

@@ -1 +1,3 @@
-7.4.1
+1079973bd513b69fb56becc7fe678c03449b30c3
+# A commit on the 8.5.0 release branch with support for facts.
+# TODO: Update to 8.5.0 when released.