Before this, pmacs sent and consumed LSP `Position.character` as raw
UTF-8 byte offsets while advertising no `positionEncoding`, so per
the LSP spec every non-3.17 server assumed UTF-16. rust-analyzer is
lenient; clangd/gopls/pyright are not — any non-ASCII byte before a
position silently corrupted definition jumps, diagnostic spans,
hover targets, and formatting edits. This is the correctness gate
before Python/C/C++/Go.
- Negotiation: advertise `general.positionEncodings:["utf-8","utf-16"]`;
honour the server's `capabilities.positionEncoding`; default UTF-16
(LSP spec default) when absent. Stored per-LspClient.
- Codec: per-line byte<->utf-8/utf-16. UTF-8 is an identity fast
path; mid-surrogate / mid-codepoint positions clamp to the
containing char's start (a unit test caught and fixed an overshoot
in the first cut).
- Document cache: (server,uri)->text mirrored from did_open /
did_change_full, dropped on did_close and at every teardown site
(start_generation / on_exit / forget) alongside the existing drain.
- One conversion at the Rust boundary: a recursive JSON Position
rewriter at the two inbound seams (absorb_routed_response,
absorb_publish_diagnostics) plus outbound at request-build. Zero
store / Lua / consumer changes — completion popup, diagnostics
gutter, and lsp.lua all stay byte-uniform.
- Non-destructive fallback: a Position on a line absent from the
cached doc (cross-file / not-yet-opened) is left unconverted, not
collapsed to 0. Correct production behaviour (cross-file encoding
is v0.2, tied to deferred cross-file nav) and fixes the m4_12
definition tests.
Tests: 6 lib unit tests (negotiation default, utf-8 identity, utf-16
non-ASCII round-trip, astral surrogate pair, nth_line EOF semantics,
recursive rewrite). pmacs_fake_lsp `posecho` mode (advertises
utf-16, echoes the wire position into the result uri as `pos:N`);
end-to-end m4 test asserts both directions independently and
discriminatingly against a `é=x` fixture.
Gate: fmt clean; clippy --all-targets -D warnings clean; lib
1229/0; m4_acceptance 60/0; m9_1 18/0; m8_1/m8_9/m8_10 green.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Levi Neuwirth
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