feat(errors): panic(msg) + assert(cond, msg) with file:line — no raw crashes (#8)

RFC decision (the split the issue recommended): programmer bugs abort loud and
located; recoverable failures become values. This ships the first half.

panic(msg) prints `file:line: panic: <msg>` to stderr and aborts the process with
exit code 1 — a clear, located error instead of a segfault or a silent wrong
result. assert(cond, msg) is the guarded form: it aborts with `file:line:
assertion failed: <msg>` only when cond is false, otherwise execution continues.
The location is baked in at compile time (the call node carries its source line,
g_src_name carries the file); the message is any string.

Both lower in emit_call to an fprintf-to-stderr + exit(1) + unreachable tail
(assert branches on the condition first). @fprintf and the format constant are
declared on demand (g_uses_panic), so a program that never panics is unchanged —
and the compiler's own source uses neither, so the C-free bootstrap fixpoint holds.

- panic/assert registered as builtins across the vocabulary (ludic_syntax.h, the
  JetBrains lexer, the TextMate grammar) and documented (docs/language/builtins/)
- examples/library/errors.ludic covers the success path (asserts hold, program
  runs to the end); a panic_case in the suite covers the failure path (non-zero
  exit + the located stderr message). x test is now 69 checks.

Deferred: recoverable failures as `try`/`else` values (needs the tagged-union
type system, #1) and a top-level `recover` for the dev game loop.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tools/editors/jetbrains/src/main/kotlin/io/ludic/ide/LudicTokens.kt

@@ -64,7 +64,7 @@ object LudicVocabulary {
         "sprites_load", "draw_sprite", "draw_sprite_scaled", "ui_build", "ui_open",
         "ui_tick", "ui_render", "ui_clicked", "ui_set_text", "ui_set_int", "ui_focus",
         "ui_focused", "ui_visible", "key", "reg", "set_reg", "self", "save", "load",
-        "status", "print", "string", "quit",
+        "status", "print", "string", "quit", "panic", "assert",
         // compiler intrinsics: the floor the Ludic-written runtime stands on
         "bytes", "words", "resize", "free", "fill",         "arg_count", "arg", "file_stderr", "file_stdout",
         "offset",

tools/editors/shared/ludic.tmLanguage.json

@@ -204,7 +204,7 @@
         {
           "comment": "the runtime surface — every name here resolves to rt_<name> in runtime/native",
           "name": "support.function.builtin.ludic",
-          "match": "\\b(min|max|abs|clamp|seed|rng_range|rng_chance|fixed|floor|map_size|map_row|tile|clear|present|fill_rect|frame_rect|put_px|text|text_int|font_load|text_ttf|text_w|text_h|image_load|draw_image|draw_image_scaled|draw_9slice|png_load|sprites_load|draw_sprite|draw_sprite_scaled|ui_build|ui_open|ui_tick|ui_render|ui_clicked|ui_set_text|ui_set_int|ui_focus|ui_focused|ui_visible|key|reg|set_reg|self|save|load|status|print|string|quit)\\b(?=\\s*\\()"
+          "match": "\\b(min|max|abs|clamp|seed|rng_range|rng_chance|fixed|floor|map_size|map_row|tile|clear|present|fill_rect|frame_rect|put_px|text|text_int|font_load|text_ttf|text_w|text_h|image_load|draw_image|draw_image_scaled|draw_9slice|png_load|sprites_load|draw_sprite|draw_sprite_scaled|ui_build|ui_open|ui_tick|ui_render|ui_clicked|ui_set_text|ui_set_int|ui_focus|ui_focused|ui_visible|key|reg|set_reg|self|save|load|status|print|string|quit|panic|assert)\\b(?=\\s*\\()"
         },
         {
           "comment": "compiler intrinsics — these lower straight to libc or the OS",

tools/editors/vscode/syntaxes/ludic.tmLanguage.json

@@ -204,7 +204,7 @@
         {
           "comment": "the runtime surface — every name here resolves to rt_<name> in runtime/native",
           "name": "support.function.builtin.ludic",
-          "match": "\\b(min|max|abs|clamp|seed|rng_range|rng_chance|fixed|floor|map_size|map_row|tile|clear|present|fill_rect|frame_rect|put_px|text|text_int|font_load|text_ttf|text_w|text_h|image_load|draw_image|draw_image_scaled|draw_9slice|png_load|sprites_load|draw_sprite|draw_sprite_scaled|ui_build|ui_open|ui_tick|ui_render|ui_clicked|ui_set_text|ui_set_int|ui_focus|ui_focused|ui_visible|key|reg|set_reg|self|save|load|status|print|string|quit)\\b(?=\\s*\\()"
+          "match": "\\b(min|max|abs|clamp|seed|rng_range|rng_chance|fixed|floor|map_size|map_row|tile|clear|present|fill_rect|frame_rect|put_px|text|text_int|font_load|text_ttf|text_w|text_h|image_load|draw_image|draw_image_scaled|draw_9slice|png_load|sprites_load|draw_sprite|draw_sprite_scaled|ui_build|ui_open|ui_tick|ui_render|ui_clicked|ui_set_text|ui_set_int|ui_focus|ui_focused|ui_visible|key|reg|set_reg|self|save|load|status|print|string|quit|panic|assert)\\b(?=\\s*\\()"
         },
         {
           "comment": "compiler intrinsics — these lower straight to libc or the OS",

tools/ludic-tools/ludic_syntax.h

@@ -141,6 +141,8 @@ static const LBuiltin LUDIC_BUILTINS[] = {
  {"print","print(x)","Print a value (int or string) and a newline to stdout."},
  {"string","string(x) -> string","Convert an int/bool/fixed to text (a string passes through)."},
  {"quit","quit()","Stop the frame loop and exit."},
+ {"panic","panic(msg: string)","Print `file:line: panic: msg` to stderr and abort (exit 1) — a located error, not a crash."},
+ {"assert","assert(cond: bool, msg: string)","Abort with `file:line: assertion failed: msg` when cond is false — for programmer-bug invariants."},
  {0,0,0}
 };
 

tools/x/test.ludic

@@ -75,6 +75,18 @@ function spec_case(path: pointer, exp: pointer) -> void {
   else { bad2(path, `rc={string(rc)} last=[{summary}]`) }
 }
 
+# issue #8: the failure path — a panic must abort with a non-zero exit and a
+# `file:line: panic: <msg>` line on stderr (stdout is unaffected up to the panic).
+function panic_case() -> void {
+  write_file("/tmp/x_panic.ludic", "program P { entry { print(7); panic(\"boom\") } }\n")
+  if not shq("bin/ludicc /tmp/x_panic.ludic > /tmp/x_panic.ll 2>/dev/null") { bad("panic example did not compile"); return }
+  if not shq(`{cc()} -O2 /tmp/x_panic.ll -o /tmp/x_panic 2>/dev/null`) { bad("panic example did not link"); return }
+  let rc = sh("/tmp/x_panic > /tmp/x_panic.out 2>/tmp/x_panic.err")
+  let msg = capture_line("cat /tmp/x_panic.err")
+  if (rc != 0) and shq("grep -q 'panic: boom' /tmp/x_panic.err") { ok(`panic aborts non-zero with a located stderr message ({msg})`) }
+  else { bad2("panic", `rc={string(rc)} err=[{msg}]`) }
+}
+
 function cmd_test() -> int {
   PASS = 0
   FAIL = 0
@@ -129,6 +141,8 @@ function cmd_test() -> int {
   feat_case("library/render", "", "1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18", "render.ludic (Screen pixel/oval/camera/clip/blend_mode/measure_text + Camera set/follow/shake, verified by pixel readback)")
   feat_case("library/lighting", "", "1 2 3 4 5 6 7 8 9 10 11 12 13 14", "lighting.ludic (Light ambient/point radial falloff + occluder hard shadows — 2D light accumulation, verified by pixel readback)")
   spec_case("library/testing", "== 6 passed, 0 failed ==")
+  feat_case("library/errors", "", "5 10 0 7 1", "errors.ludic (assert guards an invariant, holds -> runs to the end; issue #8 success path)")
+  panic_case()
   feat_case("library/logging", "", "0 5 2 1", "logging.ludic (Log levels, set_level/level threshold, structured fields)")
   # Os known-folders/arch and Fs.list read the BSD utsname/dirent layout, so
   # their asserted values are macOS-specific; skip off Darwin (see is_darwin).