Allow user provided platform constraints

Author: jkurland-roku

toolchain/extensions/llvm.bzl

@@ -34,6 +34,20 @@ def _root_dict(roots, cls, name, strip_target):
 
     return res
 
+def _constraint_dict(tags, name):
+    constraints = {}
+
+    # Gather all the additional constraints for each target
+    for tag in tags:
+        targets = list(tag.targets)
+        if not targets:
+            targets = [""]
+        for target in targets:
+            constraints_for_target = constraints.setdefault(target, [])
+            constraints_for_target.extend([str(c) for c in tag.constraints])
+
+    return constraints
+
 def _llvm_impl_(module_ctx):
     for mod in module_ctx.modules:
         if not mod.is_root:
@@ -49,6 +63,14 @@ def _llvm_impl_(module_ctx):
             }
             attrs["toolchain_roots"] = _root_dict([root for root in mod.tags.toolchain_root if root.name == name], "toolchain_root", name, True)
             attrs["sysroot"] = _root_dict([sysroot for sysroot in mod.tags.sysroot if sysroot.name == name], "sysroot", name, False)
+            attrs["extra_exec_compatible_with"] = _constraint_dict(
+                [tag for tag in mod.tags.extra_exec_compatible_with if tag.name == name],
+                name,
+            )
+            attrs["extra_target_compatible_with"] = _constraint_dict(
+                [tag for tag in mod.tags.extra_target_compatible_with if tag.name == name],
+                name,
+            )
 
             llvm_toolchain(
                 **attrs
@@ -95,5 +117,19 @@ llvm = module_extension(
                 "path": attr.string(doc = "Absolute path to the sysroot."),
             },
         ),
+        "extra_exec_compatible_with": tag_class(
+            attrs = {
+                "name": attr.string(doc = "Same name as the toolchain tag.", default = "llvm_toolchain"),
+                "targets": attr.string_list(doc = "Specific targets, if any; empty list means this applies to all."),
+                "constraints": attr.label_list(doc = "List of extra constraints to add to exec_compatible_with for the generated toolchains."),
+            },
+        ),
+        "extra_target_compatible_with": tag_class(
+            attrs = {
+                "name": attr.string(doc = "Same name as the toolchain tag.", default = "llvm_toolchain"),
+                "targets": attr.string_list(doc = "Specific targets, if any; empty list means this applies to all."),
+                "constraints": attr.label_list(doc = "List of extra constraints to add to target_compatible_with for the generated toolchains."),
+            },
+        ),
     },
 )

toolchain/internal/configure.bzl

@@ -59,6 +59,8 @@ def _join(path1, path2):
 def llvm_config_impl(rctx):
     _check_os_arch_keys(rctx.attr.sysroot)
     _check_os_arch_keys(rctx.attr.cxx_builtin_include_directories)
+    _check_os_arch_keys(rctx.attr.extra_exec_compatible_with)
+    _check_os_arch_keys(rctx.attr.extra_target_compatible_with)
 
     os = _os(rctx)
     if os == "windows":
@@ -166,6 +168,8 @@ def llvm_config_impl(rctx):
         unfiltered_compile_flags_dict = rctx.attr.unfiltered_compile_flags,
         llvm_version = llvm_version,
         extra_compiler_files = rctx.attr.extra_compiler_files,
+        extra_exec_compatible_with = rctx.attr.extra_exec_compatible_with,
+        extra_target_compatible_with = rctx.attr.extra_target_compatible_with,
     )
     exec_dl_ext = "dylib" if os == "darwin" else "so"
     cc_toolchains_str, toolchain_labels_str = _cc_toolchains_str(
@@ -380,11 +384,11 @@ toolchain(
     exec_compatible_with = [
         "@platforms//cpu:{exec_arch}",
         "@platforms//os:{exec_os_bzl}",
-    ],
+    ] + {extra_exec_compatible_with_specific} + {extra_exec_compatible_with_all_targets},
     target_compatible_with = [
         "@platforms//cpu:{target_arch}",
         "@platforms//os:{target_os_bzl}",
-    ],
+    ] + {extra_target_compatible_with_specific} + {extra_target_compatible_with_all_targets},
     target_settings = {target_settings},
     toolchain = ":cc-clang-{suffix}",
     toolchain_type = "@bazel_tools//tools/cpp:toolchain_type",
@@ -543,6 +547,10 @@ cc_toolchain(
         ]),
         extra_compiler_files = ("\"%s\"," % str(toolchain_info.extra_compiler_files)) if toolchain_info.extra_compiler_files else "",
         major_llvm_version = major_llvm_version,
+        extra_exec_compatible_with_specific = toolchain_info.extra_exec_compatible_with.get(target_pair, []),
+        extra_target_compatible_with_specific = toolchain_info.extra_target_compatible_with.get(target_pair, []),
+        extra_exec_compatible_with_all_targets = toolchain_info.extra_exec_compatible_with.get("", []),
+        extra_target_compatible_with_all_targets = toolchain_info.extra_target_compatible_with.get("", []),
     )
 
 def _convenience_targets_str(rctx, use_absolute_paths, llvm_dist_rel_path, llvm_dist_label_prefix, exec_dl_ext):

toolchain/internal/repo.bzl

@@ -271,6 +271,14 @@ llvm_config_attrs.update({
         default = False,
         doc = "Use absolute paths in the toolchain. Avoids sandbox overhead.",
     ),
+    "extra_exec_compatible_with": attr.string_list_dict(
+        mandatory = False,
+        doc = "Extra constraints to be added to exec_compatible_with for each target",
+    ),
+    "extra_target_compatible_with": attr.string_list_dict(
+        mandatory = False,
+        doc = "Extra constraints to be added to target_compatible_with for each target",
+    ),
     "_cc_toolchain_config_bzl": attr.label(
         default = "//toolchain:cc_toolchain_config.bzl",
     ),