feat(formula): one AST for both spreadsheet formula syntaxes

[andiwand]

🤖 Generated with Claude Code

Step 3.1 of docs/design/spreadsheet-editing.md — the read side of formulas. First of four; the dependency graph, the view and the .ods cached value follow on top of this.

What it does

src/odr/internal/formula parses what a table:formula and an <f> state into one AST. The two syntaxes share their expression grammar — the same operators at the same precedence — and differ over three things, so one recursive descent takes a Syntax and branches where they part:

	OpenFormula	OOXML
reference	[$'My Sheet'.$A$1:.B2]	'My Sheet'!$A$1:B2
argument separator	;	,
array row separator	|	;

Read: cell references, ranges, whole columns (A:A), the $ of each axis, sheet-qualified and external references, named expressions, functions, arrays, errors, and the operators. A named expression and a reference over several sheets (Sheet1:Sheet3!A1) stay the spelling the file states — nothing resolves one.

Nothing evaluates anything: that is step 4.

What it reuses

Two commits come first. TablePosition gains the non-throwing
try_to_column_num / try_to_row_num the parser needs — case folded, and no
longer wrapping past the index range — and the ascii character classes rtf, the
odf value cursor and this parser each wrote for themselves move into
util::string. Then internal::TextCursor takes the cursor layer both the odf
value cursor and this parser had written: peek, take, advance, seek,
skip_whitespace, consume, take_while.

Two decisions worth a look

• A formula that does not parse answers nothing. A caller reads no reference out of one it cannot read, which keeps the dependency graph honest rather than half-built.
• A spelling no position can hold is a name. A0 (rows are 1-based) and ABCDEFGHI1 (past what an index holds) are names, not refused parses — which is what a sheet calls them too, and a name carries no dependency.

Test

43 cases in test/src/internal/formula/formula_parser_test.cpp, inline strings only. They pin the precedence a sheet has (-2^2 is 4, -3% is -0.03), the LOG10( ambiguity against the reference LOG10, and each dialect's own spellings.