Rollup merge of #131830 - hoodmane:emscripten-wasm-eh, r=workingjubilee

Add support for wasm exception handling to Emscripten target

This is a draft because we need some additional setting for the Emscripten target to select between the old exception handling and the new exception handling. I don't know how to add a setting like that, would appreciate advice from Rust folks. We could maybe choose to use the new exception handling if `Ctarget-feature=+exception-handling` is passed? I tried this but I get errors from llvm so I'm not doing it right.

compiler/rustc_session/src/config/cfg.rs

@@ -143,6 +143,7 @@ pub(crate) fn disallow_cfgs(sess: &Session, user_cfgs: &Cfg) {
             | (sym::target_has_atomic_load_store, Some(_))
             | (sym::target_thread_local, None) => disallow(cfg, "--target"),
             (sym::fmt_debug, None | Some(_)) => disallow(cfg, "-Z fmt-debug"),
+            (sym::emscripten_wasm_eh, None | Some(_)) => disallow(cfg, "-Z emscripten_wasm_eh"),
             _ => {}
         }
     }
@@ -295,6 +296,10 @@ pub(crate) fn default_configuration(sess: &Session) -> Cfg {
         ins_none!(sym::ub_checks);
     }
 
+    // Nightly-only implementation detail for the `panic_unwind` and `unwind` crates.
+    if sess.is_nightly_build() && sess.opts.unstable_opts.emscripten_wasm_eh {
+        ins_none!(sym::emscripten_wasm_eh);
+    }
     ret
 }
 

compiler/rustc_session/src/options.rs

@@ -1771,6 +1771,8 @@ options! {
         "emit a section containing stack size metadata (default: no)"),
     emit_thin_lto: bool = (true, parse_bool, [TRACKED],
         "emit the bc module with thin LTO info (default: yes)"),
+    emscripten_wasm_eh: bool = (false, parse_bool, [TRACKED],
+        "Use WebAssembly error handling for wasm32-unknown-emscripten"),
     enforce_type_length_limit: bool = (false, parse_bool, [TRACKED],
         "enforce the type length limit when monomorphizing instances in codegen"),
     export_executable_symbols: bool = (false, parse_bool, [TRACKED],