WIP: prototype of wasm host as run_binary wrapper #1210

alexeagle · 2025-11-16T17:18:01Z

See comments in tools/run_binary/main.go

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chatgpt-codex-connector · 2025-11-16T17:20:29Z

lib/private/run_binary.bzl

    ctx.actions.run(
        outputs = outputs,
        inputs = inputs,
-        executable = ctx.executable.tool,
+        executable = ctx.executable.tool_launcher,
        arguments = [args],


Keep running the user-specified tool

The run_binary action now executes only ctx.executable.tool_launcher and never references ctx.executable.tool. Because the tool attribute is no longer added to the action’s inputs or invoked, every run_binary target will invoke the launcher binary regardless of what tool the rule declares, and the declared tool will not even be built when the action runs. This completely regresses the behavior of run_binary and breaks all existing usages of the rule.

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chatgpt-codex-connector · 2025-11-16T17:20:29Z

tools/run_binary/main.go

+	// Load wasm code by reading /Users/alexeagle/Projects/bazel-lib/bazel-bin/path/to/package/tool_/tool.wasm
+	wasmCode, err := os.ReadFile("/Users/alexeagle/Projects/bazel-lib/bazel-bin/path/to/package/tool_/tool.wasm")
+	if err != nil {


Don’t hard-code developer path to the WASM binary

The new launcher reads a WASM module from the absolute path /Users/alexeagle/Projects/bazel-lib/bazel-bin/path/to/package/tool_/tool.wasm. That path only exists on the author’s workstation, so the launcher will fail immediately on any other machine, workspace location, or remote executor. There is currently no way for Bazel to tell the launcher which tool to run, making the wrapper unusable for any run_binary target.

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chatgpt-codex-connector · 2025-11-16T17:20:30Z

tools/run_binary/main.go

+	_, err = spawnFunc.Call(store, "bazel-out/darwin_arm64-fastbuild/bin/path/to/package/output.txt")
+	if err != nil {


Output path is hard-coded to one platform

The launcher calls the WASM export with the literal path "bazel-out/darwin_arm64-fastbuild/bin/path/to/package/output.txt". This ignores the outs and args declared on the run_binary rule and forces every action to write to a darwin/arm64 fastbuild path, even when the build is running on Linux, on a different configuration, or produces a different file. As written the wrapper cannot produce the outputs requested by the Bazel action, so every run_binary target will either fail or write to the wrong location.

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aspect-workflows · 2025-11-16T17:23:11Z

Bazel 8 (Test)

⚠️ Buildkite build #252 failed.

//lib/tests/run_binary_expansions:expansions failed to build

run_binary failed: error executing RunBinary command (from target //lib/tests/run_binary_expansions:expansions) bazel-out/k8-opt-exec-ST-d57f47055a04/bin/tools/run_binary/run_binary_/run_binary bazel-out/k8-fastbuild/bin/lib/tests/run_binary_expansions/expansions_out ... (remaining 19 arguments skipped)
 
Use --sandbox_debug to see verbose messages from the sandbox and retain the sandbox build root for debugging
 
Failed to read wasm code: open /Users/alexeagle/Projects/bazel-lib/bazel-bin/path/to/package/wasm_tool_/wasm_tool.wasm: no such file or directory

//lib/tests/run_binary:dir_a failed to build

run_binary failed: error executing SomeAction command (from target //lib/tests/run_binary:dir_a) bazel-out/k8-opt-exec-ST-d57f47055a04/bin/tools/run_binary/run_binary_/run_binary bazel-out/k8-fastbuild/bin/lib/tests/run_binary/dir_a_out
 
Use --sandbox_debug to see verbose messages from the sandbox and retain the sandbox build root for debugging
 
Failed to read wasm code: open /Users/alexeagle/Projects/bazel-lib/bazel-bin/path/to/package/wasm_tool_/wasm_tool.wasm: no such file or directory

//lib/tests/stamping:run_stamper failed to build

run_binary failed: error executing RunBinary command (from target //lib/tests/stamping:run_stamper) bazel-out/k8-opt-exec-ST-d57f47055a04/bin/tools/run_binary/run_binary_/run_binary bazel-out/k8-fastbuild/bin/lib/tests/stamping/stamped
 
Use --sandbox_debug to see verbose messages from the sandbox and retain the sandbox build root for debugging
 
Failed to read wasm code: open /Users/alexeagle/Projects/bazel-lib/bazel-bin/path/to/package/wasm_tool_/wasm_tool.wasm: no such file or directory

//path/to/package:package failed to build

run_binary failed: error executing RunBinary command (from target //path/to/package:package) bazel-out/k8-opt-exec-ST-d57f47055a04/bin/tools/run_binary/run_binary_/run_binary bazel-out/k8-fastbuild/bin/path/to/package/output.txt
 
Use --sandbox_debug to see verbose messages from the sandbox and retain the sandbox build root for debugging
 
Failed to read wasm code: open /Users/alexeagle/Projects/bazel-lib/bazel-bin/path/to/package/wasm_tool_/wasm_tool.wasm: no such file or directory

💡 To reproduce the build failures, run

bazel build //lib/tests/run_binary_expansions:expansions //lib/tests/run_binary:dir_a //lib/tests/stamping:run_stamper //path/to/package:package

Bazel 9 (Test)

⚠️ Buildkite build #252 failed.

//lib/tests/run_binary_expansions:expansions failed to build

run_binary failed: error executing RunBinary command (from _run_binary rule target //lib/tests/run_binary_expansions:expansions) bazel-out/k8-opt-exec/bin/tools/run_binary/run_binary_/run_binary bazel-out/k8-fastbuild/bin/lib/tests/run_binary_expansions/expansions_out ... (remaining 19 arguments skipped)
 
Use --sandbox_debug to see verbose messages from the sandbox and retain the sandbox build root for debugging
 
Failed to read wasm code: open /Users/alexeagle/Projects/bazel-lib/bazel-bin/path/to/package/wasm_tool_/wasm_tool.wasm: no such file or directory

//lib/tests/stamping:run_stamper failed to build

run_binary failed: error executing RunBinary command (from _run_binary rule target //lib/tests/stamping:run_stamper) bazel-out/k8-opt-exec/bin/tools/run_binary/run_binary_/run_binary bazel-out/k8-fastbuild/bin/lib/tests/stamping/stamped
 
Use --sandbox_debug to see verbose messages from the sandbox and retain the sandbox build root for debugging
 
Failed to read wasm code: open /Users/alexeagle/Projects/bazel-lib/bazel-bin/path/to/package/wasm_tool_/wasm_tool.wasm: no such file or directory

//path/to/package:package failed to build

run_binary failed: error executing RunBinary command (from _run_binary rule target //path/to/package:package) bazel-out/k8-opt-exec/bin/tools/run_binary/run_binary_/run_binary bazel-out/k8-fastbuild/bin/path/to/package/output.txt
 
Use --sandbox_debug to see verbose messages from the sandbox and retain the sandbox build root for debugging
 
Failed to read wasm code: open /Users/alexeagle/Projects/bazel-lib/bazel-bin/path/to/package/wasm_tool_/wasm_tool.wasm: no such file or directory

//lib/tests/run_binary:dir_a failed to build

run_binary failed: error executing SomeAction command (from _run_binary rule target //lib/tests/run_binary:dir_a) bazel-out/k8-opt-exec/bin/tools/run_binary/run_binary_/run_binary bazel-out/k8-fastbuild/bin/lib/tests/run_binary/dir_a_out
 
Use --sandbox_debug to see verbose messages from the sandbox and retain the sandbox build root for debugging
 
Failed to read wasm code: open /Users/alexeagle/Projects/bazel-lib/bazel-bin/path/to/package/wasm_tool_/wasm_tool.wasm: no such file or directory

💡 To reproduce the build failures, run

bazel build //lib/tests/run_binary_expansions:expansions //lib/tests/stamping:run_stamper //path/to/package:package //lib/tests/run_binary:dir_a

WIP: prototype of wasm host as run_binary wrapper

56e8443

alexeagle requested review from dzbarsky and thesayyn November 16, 2025 17:18

chatgpt-codex-connector bot reviewed Nov 16, 2025

View reviewed changes

use wasmzero runtime, seems easier

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WIP: prototype of wasm host as run_binary wrapper #1210

WIP: prototype of wasm host as run_binary wrapper #1210

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aspect-workflows bot commented Nov 16, 2025 •

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		_, err = spawnFunc.Call(store, "bazel-out/darwin_arm64-fastbuild/bin/path/to/package/output.txt")
		if err != nil {

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