fix(beam): escape quotes and backslashes in quoted atoms

[dbrattli]

Problem

quoteErlangAtom wraps a name in single quotes without escaping its contents. A quoted Erlang atom reads the same escape sequences a string does, so two characters break it — and [<CompiledName>] reaches the atom text verbatim (via unionCaseTagName), which makes both user-reachable:

type Quoted =
    | [<CompiledName("it's")>] Apostrophe of int
    | [<CompiledName("back\\slash")>] Backslash of int

'it's'          %% syntax error — the ' closes the atom early
'back\slash'    %% compiles, but `\s` is Erlang's escape for a space

The second is the one that matters: it compiles cleanly and yields the atom back lash. Codegen and the erl_tag in reflection metadata both go through this function, so they agree on the wrong name and nothing surfaces the mismatch.

Fix

Escape \ then ' inside the quotes (backslash first, or the ones the second replace adds get escaped again).

Scope is narrow: quoteErlangAtom is only reached from AtomLit printing in ErlangPrinter. Module, export and function-clause names print raw and always come from sanitizeErlangName, which strips these characters already.

Test

tests/Beam/ReflectionTests.fs gains a DU carrying both hostile [<CompiledName>]s, next to the existing CompiledName/erl_tag regression test. It covers pattern matching and a MakeUnion → match round-trip, so the reflection tag has to land on the same atom codegen emits.

Verification

• Reproduced on the branch baseline first: the generated module failed to compile, and 'back\slash' was visible in the output.
• After the fix, erlang:atom_to_binary round-trips it's, back\slash and both'and\ exactly.
• Beam suite: 2659 passed, 0 failed (.NET 2637 / Erlang 2659), plus the entry-point program tests. Fantomas clean.

🤖 Generated with Claude Code