fix: every external-scanner grammar crashed pardes on parse (rust/cpp/python/...; e.g. opening agave cpi.rs or any tracy .cpp), Debug AND ReleaseSafe. Root cause: clang -fsanitize=function (in zig's default C UBSan set) traps at the runtime's indirect call of the scanner because grammars declare external_scanner_create() with EMPTY PARENS — a K&R non-prototype whose type hash differs from the void*(*)(void) pointer type. The ud1 trap lands on a bogus inlined line (stack.c:746), which cost the diagnosis a detour through rr (its gdbserver dies replaying past the task exit — core dump + coredumpctl worked; ud1 0x6(%eax) = SanitizerHandler kind 6 = function_type_mismatch; scanner-less c/zig grammars never crashed). Fix per review direction: -fno-sanitize=function on the grammar TUs in build.zig — uninstrumented callees make the runtime's call-site checks skip; the rest of UBSan stays live. Second half: fatal signals (SIGILL/SEGV/BUS/FPE) never run defers and bypassed the panic hook, leaving the terminal raw after a crash — root.debug.handleSegfault override now runs vaxis.recover() before std.debug.defaultHandleSegfault, verified in a raw pty (kill -ILL $PPID: rmcup + mouse resets precede the trace). Verified: rust/cpp/python opens work with real highlighting (snapstyle: keywords/strings/comments colored), agave cpi.js 2.7k-line open fine, suite 30/30, ReleaseSafe build opens rust identically.

1 files changed, 11 insertions, 2 deletions

diff --git a/build.zig b/build.zig
index beeba648..29188d48 100644
--- a/build.zig
+++ b/build.zig
@@ -163,8 +163,17 @@ pub fn build(b: *std.Build) void {
                     .linkage = .static,
                 });
                 if (libc_file) |f| lib.setLibCFile(f);
-                lib.root_module.addCSourceFile(.{ .file = dep.path(g.src ++ "/parser.c") });
-                if (g.scanner) lib.root_module.addCSourceFile(.{ .file = dep.path(g.src ++ "/scanner.c") });
+                // grammars declare external_scanner_create() with EMPTY PARENS
+                // (a K&R non-prototype, not (void)): under clang's
+                // -fsanitize=function the callee's type hash differs from the
+                // runtime's void*(*)(void) call through the pointer, so the
+                // first scanner call of ANY parse traps (function_type_mismatch,
+                // an ud1 blamed on a random inlined line). Uninstrumented
+                // callees make the runtime's call-site checks skip; the rest
+                // of UBSan stays live for the grammar code.
+                const ts_cflags = [_][]const u8{"-fno-sanitize=function"};
+                lib.root_module.addCSourceFile(.{ .file = dep.path(g.src ++ "/parser.c"), .flags = &ts_cflags });
+                if (g.scanner) lib.root_module.addCSourceFile(.{ .file = dep.path(g.src ++ "/scanner.c"), .flags = &ts_cflags });
                 lib.root_module.addIncludePath(dep.path(g.src));
                 root_mod.linkLibrary(lib);
                 if (is_emscripten) wasm_libs.append(b.allocator, lib.getEmittedBin()) catch @panic("OOM");