Fix default key logic in urls attribute

We were not using the strip_prefix attribute correctly when the default
key was being used instead of the host OS key. This resulted in the
archive being extracted without any strip_prefix value.

Author: Siddhartha Bagaria

tests/WORKSPACE

@@ -31,9 +31,9 @@ llvm_toolchain(
     name = "llvm_toolchain",
     llvm_version = LLVM_VERSION,
     # To test (manually) if the URLs feature works to fetch an archive.
-    #sha256 = {"ubuntu-20.04-x86_64": "a9ff205eb0b73ca7c86afc6432eed1c2d49133bd0d49e47b15be59bbf0dd292e"},
-    #strip_prefix = {"ubuntu-20.04-x86_64": "clang+llvm-14.0.0-x86_64-linux-gnu-ubuntu-20.04"},
-    #urls = {"ubuntu-20.04-x86_64": ["https://github.com/llvm/llvm-project/releases/download/llvmorg-14.0.0/clang+llvm-14.0.0-x86_64-linux-gnu-ubuntu-20.04.tar.xz"]},
+    #sha256 = {"": "61582215dafafb7b576ea30cc136be92c877ba1f1c31ddbbd372d6d65622fef5"},
+    #strip_prefix = {"": "clang+llvm-14.0.0-x86_64-linux-gnu-ubuntu-18.04"},
+    #urls = {"": ["https://github.com/llvm/llvm-project/releases/download/llvmorg-14.0.0/clang+llvm-14.0.0-x86_64-linux-gnu-ubuntu-18.04.tar.xz"]},
 )
 
 # This is the last known LLVM version with zlib support in ld.lld. Without zlib

toolchain/internal/llvm_distributions.bzl

@@ -255,8 +255,11 @@ def _get_auth(ctx, urls):
 
 def download_llvm(rctx):
     urls = []
+    update_sha256 = False
     if rctx.attr.urls:
         urls, sha256, strip_prefix, key = _urls(rctx)
+        if not sha256:
+            update_sha256 = True
     if not urls:
         urls, sha256, strip_prefix = _distribution_urls(rctx)
 
@@ -268,21 +271,24 @@ def download_llvm(rctx):
     )
 
     updated_attrs = _attr_dict(rctx.attr)
-    if not sha256 and key:
-        # Only using the urls attribute can result in no sha256.
-        # Report back the sha256 if the URL came from a non-empty key.
+    if update_sha256:
         updated_attrs["sha256"].update([(key, res.sha256)])
-
     return updated_attrs
 
 def _urls(rctx):
     key = _host_os_key(rctx)
 
-    urls = rctx.attr.urls.get(key, default = rctx.attr.urls.get("", default = []))
+    key_orig = key
+    if key not in rctx.attr.urls:
+        print("LLVM archive URLs missing for host OS key '%s'; checking fallback with key ''" % (key))
+        key = ""
+
+    urls = rctx.attr.urls.get(key, default = [])
     if not urls:
-        print("llvm archive urls missing for host OS key '%s' and no default provided; will try 'distribution' attribute" % (key))
-    sha256 = rctx.attr.sha256.get(key, "")
-    strip_prefix = rctx.attr.strip_prefix.get(key, "")
+        print("LLVM archive URLs missing for host OS key '%s' and no default fallback provided; will try 'distribution' attribute" % (key_orig))
+
+    sha256 = rctx.attr.sha256.get(key, default = "")
+    strip_prefix = rctx.attr.strip_prefix.get(key, default = "")
 
     return urls, sha256, strip_prefix, key