Error mapping

Two things make raw errors useless in a .n file. svelte-preprocess renders Pug with a ~50-line mixin prelude prepended, so Pug's line numbers point ~50 lines past the real one, on top of the +if / +snippet rewrites that move lines. And a Civet error inside a <script> block is relative to the block, not the file.

norns-core keeps the original source of each .n file it processes and maps both kinds of errors back:

• Pug errors become PugError with code: 'norns_pug_error', line, column, a frame over your source, and a message of the form Page.n:18:7: Pug: <message>. The prelude offset is voted from the lines of Pug's own code frame that can be found verbatim in the template; rewritten lines (| {#if x} from +if('x')) are searched in their original spelling. When the exact line cannot be found the nearest plausible one is used and the message says (approximate line).
• Civet script errors keep Civet's ParseError but get code: 'norns_civet_error' and a file-relative line, column and frame.

norns check prints these as file:line:column diagnostics, and the stage field tells you which compiler produced them. Svelte compile errors are a separate case handled by norns check through the preprocess source map; see check and diag.