grow/capacity/rate arg-type errors are positionless → editors can't squiggle the bad argument

[dvhthomas]

Summary

Runtime argument-type errors from the growth / capacity / rate builtins (e.g. grow) are returned as bare fmt.Errorf values with no source position. They reach the document as a Diagnostic carrying a line but no Column / EndColumn, so editor/LSP consumers can show the message in the gutter but cannot underline the offending argument inline — the way semantic-checker diagnostics (e.g. undefined variable) are underlined.

Repro

sx_grown = grow(100, 20%, 5)

grow's increment (2nd arg) must be a number / quantity / currency; 20% is a percentage and is correctly rejected:

grow: increment must be a number, quantity, or currency — got percentage

The diagnostic is reported, but with no character range. (Concrete consumer check: calcmark-web's POST /api/eval returns this diagnostic with range: undefined.)

Root cause

impl/interpreter/growth_functions.go (and the sibling capacity_functions.go, rate_eval.go, which share the error shape) reject arguments with a positionless error:

return decZero, fmt.Errorf(
    "%s: %s must be a number, quantity, or currency — got percentage",
    funcName, paramName)

spec/document.Diagnostic already has the fields to carry a span (Line, Column, EndLine, EndColumn), but these errors never populate Column / EndColumn — no AST position is attached, so the diagnostic is line-only downstream.

Impact

Editor/LSP consumers (e.g. calcmark-web) can render the gutter message but can't place an inline squiggle under the bad argument. Users see "there's an error on this line" but not "this token is the problem" — a noticeable gap vs. semantic-checker errors, which underline the exact token.

Suggested fix (either is sufficient)

1. Interpreter — when these builtins reject an argument, attach that argument's AST Range to the emitted Diagnostic (the call node knows each argument's position). Consumers already map a diagnostic Range → inline underline, so this lights up with zero consumer changes.

2. Semantic checker (cleaner long-term) — teach the checker the parameter-type contracts for these builtins (e.g. grow's increment ∈ {number, quantity, currency}) so invalid arguments are caught at check time with a Range, the same path that already produces ranged diagnostics for undefined variables. This also surfaces the error earlier, before evaluation.

Notes

Found during a fit-and-finish pass on calcmark-web. The same positionless-error shape affects other runtime type errors too (e.g. currency ÷ currency), which share the identical "gutter yes, squiggle no" symptom.