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feat(compiler): Stub panic with unreachable to prevent bad codegen #2382

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feat(compiler): Stub panic with unreachable to prevent bad codegen #2382

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8eacbd2
feat(compiler): Stub panic with unreachable to prevent bad codegen
spotandjake Apr 3, 2026
dfa54d6
fix: skip test in js mode
spotandjake Apr 3, 2026
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37 changes: 25 additions & 12 deletions compiler/src/codegen/compcore.re
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Original file line number Diff line number Diff line change
Expand Up @@ -143,20 +143,33 @@ let get_metadata_ptr = wasm_mod =>
let get_grain_imported_name = (mod_, name) => Ident.unique_name(name);

let call_panic_handler = (wasm_mod, env, args) => {
let args = [
Expression.Global_get.make(
switch (env.compilation_mode) {
| Runtime =>
Expression.Block.make(
wasm_mod,
resolve_global(~env, panic_with_exception_name),
gensym_label("runtime_panic_stub"),
List.fold_left(
(acc, arg) => [Expression.Drop.make(wasm_mod, arg), ...acc],
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@ospencer ospencer May 3, 2026

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This is a little weird to me. This is only the exception being passed to the panic handler, so there's no sense in keeping it around. We should be able to just emit unreachable and have it be a little cleaner.

[Expression.Unreachable.make(wasm_mod)],
args,
),
)
| _ =>
let args = [
Expression.Global_get.make(
wasm_mod,
resolve_global(~env, panic_with_exception_name),
Type.int32,
),
...args,
];
Expression.Call.make(
wasm_mod,
resolve_func(~env, panic_with_exception_name),
args,
Type.int32,
),
...args,
];
Expression.Call.make(
wasm_mod,
resolve_func(~env, panic_with_exception_name),
args,
Type.int32,
);
);
};
};

let call_malloc = (wasm_mod, env, args) => {
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12 changes: 12 additions & 0 deletions compiler/test/suites/runtime.re
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,19 @@ describe("runtime", ({test, testSkip}) => {
let test_or_skip =
Sys.backend_type == Other("js_of_ocaml") ? testSkip : test;

let assertRunError = makeErrorRunner(test_or_skip);
let assertRuntime = makeRuntimeRunner(test_or_skip);

assertRunError(
~config_fn=() => {Grain_utils.Config.compilation_mode := Runtime},
"runtime_mode_panics",
{|
let arr = [> 1, 2, 3]
provide let x = arr[10]
|},
"RuntimeError: unreachable",
);

assertRuntime("numbers.test");

assertRuntime("unsafe/wasmf32.test");
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