emscripten-core · sbc100 · Feb 24, 2026 · Feb 20, 2026 · Feb 20, 2026 · Feb 22, 2026
diff --git a/.circleci/config.yml b/.circleci/config.yml
@@ -374,8 +374,7 @@ workflows:
               bazel_version: 
                 - "7.x"
                 - "8.x"
-              # https://github.com/emscripten-core/emsdk/issues/1642
-              # - "9.x"
+                - "9.x"
   test-bazel-windows:
     jobs:
       - test-bazel-windows:

diff --git a/bazel/MODULE.bazel b/bazel/MODULE.bazel
@@ -8,11 +8,11 @@ bazel_dep(name = "bazel_skylib", version = "1.8.2")
 bazel_dep(name = "aspect_rules_js", version = "2.9.2")
 bazel_dep(name = "rules_nodejs", version = "6.7.3")
 bazel_dep(name = "rules_cc", version = "0.2.16")
-bazel_dep(name = "rules_python", version = "1.8.3")
+bazel_dep(name = "rules_python", version = "1.8.4")
 
 python = use_extension("@rules_python//python/extensions:python.bzl", "python")
 python.toolchain(
-    python_version = "3.13",
+    python_version = "3.14",
 )
 
 node = use_extension("@rules_nodejs//nodejs:extensions.bzl", "node")

diff --git a/bazel/emscripten_toolchain/emar.sh b/bazel/emscripten_toolchain/emar.sh
@@ -2,4 +2,4 @@
 
 source $(dirname $0)/env.sh
 
-exec python3 $EMSCRIPTEN/emar.py "$@"
+exec $EMSDK_PYTHON $EMSCRIPTEN/emar.py "$@"
diff --git a/bazel/emscripten_toolchain/emcc.sh b/bazel/emscripten_toolchain/emcc.sh
@@ -2,4 +2,4 @@
 
 source $(dirname $0)/env.sh
 
-exec python3 $EMSCRIPTEN/emcc.py "$@"
+exec $EMSDK_PYTHON $EMSCRIPTEN/emcc.py "$@"
diff --git a/bazel/emscripten_toolchain/emcc_link.sh b/bazel/emscripten_toolchain/emcc_link.sh
@@ -2,4 +2,4 @@
 
 source $(dirname $0)/env.sh
 
-exec python3 $(dirname $0)/link_wrapper.py "$@"
+exec $EMSDK_PYTHON $(dirname $0)/link_wrapper.py "$@"
diff --git a/bazel/emscripten_toolchain/toolchain.bzl b/bazel/emscripten_toolchain/toolchain.bzl
@@ -75,6 +75,11 @@ def _impl(ctx):
 
     nodejs_path = ctx.file.nodejs_bin.path
 
+    python_exec_runtime = (
+        ctx.toolchains["@rules_python//python:exec_tools_toolchain_type"].
+            exec_tools.exec_interpreter[platform_common.ToolchainInfo].py3_runtime
+        )
+
     builtin_sysroot = emscripten_dir + "/emscripten/cache/sysroot"
 
     emcc_script = "emcc.%s" % ctx.attr.script_extension
@@ -1078,6 +1083,10 @@ def _impl(ctx):
                     key = "NODE_JS_PATH",
                     value = nodejs_path,
                 ),
+                env_entry(
+                    key = "EMSDK_PYTHON",
+                    value = python_exec_runtime.interpreter.path,
+                ),
             ],
         ),
         # Use llvm backend.  Off by default, enabled via --features=llvm_backend
@@ -1156,4 +1165,23 @@ emscripten_cc_toolchain_config_rule = rule(
         "script_extension": attr.string(mandatory = True, values = ["sh", "bat"]),
     },
     provides = [CcToolchainConfigInfo],
+    toolchains = [
+        "@rules_python//python:exec_tools_toolchain_type",
+    ]
+)
+
+def _python_interpreter_files_impl(ctx):
+    python_exec_runtime = (
+        ctx.toolchains["@rules_python//python:exec_tools_toolchain_type"].
+            exec_tools.exec_interpreter[platform_common.ToolchainInfo].py3_runtime
+        )
+
+    return DefaultInfo(files = python_exec_runtime.files)
+
+
+emscripten_python_interpreter_files = rule(
+    implementation = _python_interpreter_files_impl,
+    toolchains = [
+        "@rules_python//python:exec_tools_toolchain_type",
+    ]
 )
diff --git a/bazel/remote_emscripten_repository.bzl b/bazel/remote_emscripten_repository.bzl
@@ -1,6 +1,6 @@
 load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
 load("@rules_cc//cc:defs.bzl", "cc_toolchain", "cc_toolchain_suite")
-load("//emscripten_toolchain:toolchain.bzl", "emscripten_cc_toolchain_config_rule")
+load("//emscripten_toolchain:toolchain.bzl", "emscripten_cc_toolchain_config_rule", "emscripten_python_interpreter_files")
 load(":emscripten_build_file.bzl", "EMSCRIPTEN_BUILD_FILE_CONTENT_TEMPLATE")
 
 def remote_emscripten_repository(
@@ -45,6 +45,7 @@ def create_toolchains(name, repo_name, exec_compatible_with):
     ar_files_name, ar_files_target = _get_name_and_target("ar_files_" + name)
     all_files_name, all_files_target = _get_name_and_target("all_files_" + name)
     cc_wasm_name, cc_wasm_target = _get_name_and_target("cc-compiler-wasm-" + name)
+    python_interpreter_name, python_interpreter_target = _get_name_and_target("python_interpreter-" + name)
 
     wasm_name = "wasm-" + name
 
@@ -54,13 +55,18 @@ def create_toolchains(name, repo_name, exec_compatible_with):
     repo_linker_files_target = remote_repo + ":linker_files"
     repo_ar_files_target = remote_repo + ":ar_files"
 
+    emscripten_python_interpreter_files(
+        name = python_interpreter_name,
+    )
+
     native.filegroup(
         name = common_files_name,
         srcs = [
             "@emscripten_cache//:emscripten_config",
             "@emsdk//emscripten_toolchain:env.sh",
             "@emsdk//emscripten_toolchain:env.bat",
             "@nodejs//:node_files",
+            python_interpreter_target,
         ],
     )
Original file line number	Diff line number	Diff line change
Expand Up		@@ -2,4 +2,4 @@

		source $(dirname $0)/env.sh

		exec python3 $EMSCRIPTEN/emar.py "$@"
		exec $EMSDK_PYTHON $EMSCRIPTEN/emar.py "$@"
Copy link Collaborator sbc100 Feb 22, 2026 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others. Learn more. I wonder if could now maybe remove these custom launcher scripts and just use the standard emcc launcher shell script (as a followup, no in this PR) I guess it depends what else in env.sh is needed? Copy link Contributor Author DoDoENT Feb 23, 2026 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others. Learn more. I actually tried that in one of my unsuccessful iterations. I replaced all those scripts with pure Python, presented them to Bazel via `py_binary`, and then gave those binaries to the `cc_toolchain`. The first problem was that binaries were resolved in the "target context (WASM)" instead of the "exec" context, which then tried to run the "WASM version of Python", which doesn't exist. I circumvented that by creating a transitioned binary in `exec` context, and that almost worked, except final compilation attempts failed because `execv("/path/to/python/wrapper")` failed. I didn't investigate deeply enough to find out what was wrong there, and instead backtracked to pursuing adding Python interpreter runfiles to the toolchain context, so they end up in the sandbox. My first working solution required a patch to `rules_python`, which I created a PR for, but the `rules_python` author then told me this wasn't how it is supposed to be used and instructed me to research the Python exec toolchain. I did that, and this solution now works, so I created this PR. In the future, I'll probably revisit this approach that uses pure Python without any shell wrappers, but I still need to get better at Bazel before that (I'm still learning it).