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docs/bugs: the fix for each finding, and the status of the older repros #545

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68 changes: 55 additions & 13 deletions docs/bugs/native-ts-graphics-findings.md
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Original file line number Diff line number Diff line change
Expand Up @@ -12,17 +12,22 @@ of 2026-10-06, on Windows 11, 2026-10-11. Run each repro with:
tslang --emit=jit --jit-cache=false docs/bugs/ntg_<name>.ts
```

Every repro below still fails on that build: a failed assertion (exit code 3), a compile error,
or a compiler crash.

| # | Issue | Kind | Repro |
|---|---|---|---|
| 1 | Comparing `Opaque` with `Opaque \| null` crashes the compiler | Compiler crash, no message | `ntg_opaque_nullable_compare.ts` |
| 2 | Boolean array elements read back wrong | Wrong value, silent | `ntg_boolean_array_elements.ts` |
| 3 | `let s = 0` is an integer, so `s += 1.5` truncates | Wrong value, silent | `ntg_let_zero_is_integer.ts` |
| 4 | Escapes not processed in templates with substitutions | Wrong value, silent | `ntg_template_literal_escape.ts` |
| 5 | `Math.max` of negative numbers returns 2.2e-308 | Wrong value, silent (default lib) | `ntg_math_max_negative.ts` |
| 6 | `boolean && (Class \| null)` as a condition fails to compile | Compile error | `ntg_and_nullable_class.ts` |
Every repro below failed on that build: a failed assertion (exit code 3), a compile error, or a
compiler crash.

**Status (2026-10-11):** each issue has a fix with a regression test in the compiler's suite
(`tslang/test/tester`); the "Fix" column links it. Issue 3 is deliberate (integer literals are
`s32`), so its fix is a warning rather than a change of type, and `ntg_let_zero_is_integer.ts`
keeps failing by design. The repros stay here as the record of what was reported.

| # | Issue | Kind | Repro | Fix |
|---|---|---|---|---|
| 1 | Comparing `Opaque` with `Opaque \| null` crashes the compiler | Compiler crash, no message | `ntg_opaque_nullable_compare.ts` | [#536](https://github.com/ASDAlexander77/TypeScriptCompiler/pull/536) |
| 2 | Boolean array elements read back wrong | Wrong value, silent | `ntg_boolean_array_elements.ts` | [#537](https://github.com/ASDAlexander77/TypeScriptCompiler/pull/537) |
| 3 | `let s = 0` is an integer, so `s += 1.5` truncates | Wrong value, silent | `ntg_let_zero_is_integer.ts` | warning: [#544](https://github.com/ASDAlexander77/TypeScriptCompiler/pull/544) |
| 4 | Escapes not processed in templates with substitutions | Wrong value, silent | `ntg_template_literal_escape.ts` | [#539](https://github.com/ASDAlexander77/TypeScriptCompiler/pull/539) |
| 5 | `Math.max` of negative numbers returns 2.2e-308 | Wrong value, silent (default lib) | `ntg_math_max_negative.ts` | [DefaultLib#31](https://github.com/ASDAlexander77/TypeScriptCompilerDefaultLib/pull/31), and [#535](https://github.com/ASDAlexander77/TypeScriptCompiler/pull/535) for why its test passed |
| 6 | `boolean && (Class \| null)` as a condition fails to compile | Compile error | `ntg_and_nullable_class.ts` | [#540](https://github.com/ASDAlexander77/TypeScriptCompiler/pull/540), and [#541](https://github.com/ASDAlexander77/TypeScriptCompiler/pull/541) for its misplaced first error |

The silent ones (2 to 5) cost the most time: the programs compile and run, and only the output
is wrong.
Expand All @@ -47,8 +52,11 @@ no line number. Under Ninja the build step just shows `FAILED`.
**Impact and workaround:** this happened in a renderer that tracked the currently bound pipeline
to skip redundant binds. Finding it took a bisection, stubbing method bodies one at a time. The
workaround is to track such state with an integer (e.g. a pipeline index, -1 for none). From
bash the exit code shows as 127 (a missing DLL in that environment); run tslang from cmd or
PowerShell to see `0xC00000FD`.
bash the exit code shows as 127; run tslang from cmd or PowerShell to see `0xC00000FD`. (127 is
how Git Bash reports that crash, not a missing DLL.)

**Fixed by #536:** the lowering of `!=` for a nullable left operand and a tag-less union on the
right called itself again with the same operand types, until the compiler's stack ran out.

## 2. Boolean array elements read back wrong

Expand All @@ -74,6 +82,10 @@ top level and inside namespaces.
bounding boxes weren't rotated. The workaround is number arrays compared with `!= 0`. It looks
like an element-type or width mismatch (i1 vs i8?) in boolean array loads.

**Fixed by #537:** the guess was right. The literal's constant data was an LLVM vector
`<4 x i1>`, which packs the elements into bits, while elements are read one byte apart. Such data
is now an array, one byte per element.

## 3. `let s = 0` is an integer, so adding a fraction truncates

```ts
Expand All @@ -98,6 +110,10 @@ fractional value is assigned to an integer-inferred variable would catch it.

**Workaround:** write `0.0`, or annotate `: number`.

**Status:** by design: integer literals are `s32`, and that stays. #544 adds the suggested
warning: storing a `number` into a variable whose type was inferred from an integer literal says
that any fraction is dropped, and suggests declaring it `number`.

## 4. Escapes not processed in template literals with substitutions

```ts
Expand All @@ -115,6 +131,9 @@ template without substitutions (`` `a\nb` ``) and a string literal (`"a\nb"`) ar
showed a literal `\n` on screen. Split such texts into separate strings, or concatenate a
`"\n"` string literal.

**Fixed by #539:** the text around a substitution was taken as written instead of with its
escapes processed. Tagged templates and template literal types had the same mistake.

## 5. `Math.max` of negative numbers returns 2.2e-308

```ts
Expand All @@ -134,6 +153,11 @@ arguments is `-Infinity`).

**Impact and workaround:** a camera's pitch clamp broke. Clamp with explicit comparisons.

**Fixed by DefaultLib#31:** `Math.max` starts from `-Infinity` and `Math.min` from `+Infinity`,
and a NaN argument gives NaN. `tests/math.ts` didn't catch it because its `isEq(x: any, y: any)`
uses `!==`, which answered false for a `number` and an integer boxed in `any`s. #535 fixes that,
and with it the test reports this bug. `Number.MIN_VALUE` is unchanged.

## 6. `boolean && (Class | null)` as a condition fails to compile

```ts
Expand All @@ -157,6 +181,12 @@ error: failed statement

**Workaround:** nest the conditions: `if (enabled) { if (handle) { ... } }`.

**Fixed by #540:** not specific to `&&`. Any truth test of a union of null and two or more other
types failed, and `enabled && handle` is a `boolean | Handle | null`. The generated union cast
returned null for the null member, which can't be a boolean. The repro's first error, reported
at line 1 inside the comment, was a separate bug: errors in that generated code took its offsets
as positions in the user's file (#541).

---

## Seen earlier but not reproduced in minimal form
Expand Down Expand Up @@ -188,3 +218,15 @@ These aren't necessarily bugs, but each cost time because the behavior was silen
- **`number` parameters of declared C functions are doubles.** A C++ function declared with a
`float` parameter reads garbage, with no error (rotations came out as identity). The C side must
take `double`.

## The other repros in this folder

Reviewed alongside the issues above, on the same build:

| File | Status |
|---|---|
| `testFallThrough.ts` | A `default` clause without `break` jumped out of the switch instead of falling through. Fixed by [#538](https://github.com/ASDAlexander77/TypeScriptCompiler/pull/538). |
| `generic_in_generic.ts` | Nested untyped arrows with a same-named parameter, capturing a variable, failed to instantiate: their implicit type parameters had the same name. Fixed by [#542](https://github.com/ASDAlexander77/TypeScriptCompiler/pull/542). |
| `array_of_ifaces_cast.ts` | The error it expects (an array passed for an interface) was never reported; such a cast compiled to garbage. Now an error, by [#543](https://github.com/ASDAlexander77/TypeScriptCompiler/pull/543). The file still stops earlier, at errors TypeScript reports too (`return null` under strict null checks, `IToken[]` to `IStateToken[]`). |
| `bug14.ts` | Circular `typeof` / `ReturnType` aliases. TypeScript reports these as circular too; tslang reports errors and doesn't crash. Not a bug. |
| `bug21.ts` | `g: new (x: this) => x` isn't valid TypeScript (`x` isn't a type). Not a bug. |
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