Compiler warning diagnostics facility

• Type: feature
• Status: done
• Owner: —
• Unblocks: feature-lazycasing-c-imports
• Opened: 2026-06-06 (prerequisite surfaced by lazycasing ticket)

Motivation

The compiler can emit {$warning}/{$message}/{$error} from source directives, but has no general facility to raise its own warnings for accepted-but-suspect situations (e.g. a case-insensitive C-import match, a narrowing, an ignored attribute). Several planned features want to accept something yet make it visible.

Scope

• A Warn(...) path that prints file:line: warning: ... without halting.
• Consistent formatting with existing errors; routed to stderr.
• Optional: a switch to promote warnings to errors later (not required now).

Acceptance

A deliberately suspect construct emits a non-fatal warning with location; the program still compiles; no regression in error handling. First consumer: feature-lazycasing-c-imports.

Log

• 2026-06-06 — ticket opened as the warnings prerequisite for lazycasing.
• 2026-06-22 — DONE (Track A), commit a50bbd5. Added Warn(msg) / WarnAt(line, msg) in lexer.inc (next to Error): prints pascal26:<line>: warning: ..., increments WarnCount, keeps compiling. -Werror/--werror (WarnAsError) promotes the next warning to a fatal error. Re-routed the existing {$warning} directive through WarnAt so it is counted and honours -Werror. Gate green: self-host fixedpoint + threadsafe self-host byte-identical, make test + asm-emit all targets OK. First in-tree consumer is the {$warning} directive; the C-import case-insensitive match (feature-lazycasing-c-imports) is the next consumer.