[ako]

Closes #1516 (mirror of mendixlabs#1606).

actionbutton … (Action: call microflow M.F()) was a syntax error ("mismatched input ')' expecting the start of a statement"), although the same call parses in a flow body and the widget action parses without the brackets.

Cause and fix

microflowArgsV3 (mdl/grammar/domains/MDLPage.g4) required at least one argument. That one rule is the argument list of all six page-action alternatives (call microflow, call nanoflow, show page, and their MDL-DEPR020 spellings) and both flow data sources, so X() failed at every site that takes an action or a flow data source. It now takes LPAREN ( … )? RPAREN, the shape workflowCallArguments and the flow-body callArgumentList already have.

The sibling fragmentArgs had the same shape, with a worse symptom: use fragment Hdr() was not a syntax error — the page body's generic widget alternative re-read it as two widgets (type use named fragment, and type Hdr), check without a project passed it, and check -p / exec refused it with MDL-WIDGET25. Same fix.

No visitor change: buildMicroflowArgsV3 and buildFragmentArgs return nil for an empty list, so X() builds exactly the AST X builds. describe keeps writing no brackets. The change only lets refused scripts parse, so no language-version gate applies.

Audit (mxcli check, X() baseline → fixed; the bare and with-arguments forms pass both before and after everywhere)

Site	X()
button call microflow / call nanoflow / show page, and the deprecated spellings	FAIL → PASS
… X() with (…) / X() returns (…), create object E then show page X()	FAIL → PASS
container OnClick, textbox OnChange, a pluggable action property	FAIL → PASS
DataSource: microflow X() / nanoflow X()	FAIL → PASS
alter page set Action = … X() / set DataSource = microflow X()	FAIL → PASS
navigation menu item and menu document item OnClick	FAIL → PASS
fragment argument value, building-block Action: override	FAIL → PASS
use fragment Frag()	wrong AST (two bogus widgets) → right AST
flow body call microflow X()	PASS → PASS (bare call microflow X; stays an error, on purpose)
use building block X(), snippetcall (Params: ())	FAIL → FAIL (not call argument lists; left alone)

Verified

• TestEmptyCallArgumentListMeansNoArguments covers 23 sites, comparing X() with X as whole statements (DeepEqual) and their deprecation codes; its control is that X(arg = …) builds a different statement. TestFlowBodyCallStillRequiresItsBrackets pins the flow-body form.
• Revert proof: with the grammar reverted and regenerated, all 23 sites fail (22 parse errors; use fragment on statement equality).
• Real 11.13 app: baseline reports 13 syntax errors on the bug-test script; fixed, check -p --references passes, exec creates everything, mx check 0 errors. A page written entirely with () and its bracket-less twin store identical BSON (apart from $ID/GUID/name, 7 vs 7 ParameterMappings), describe identically, and re-executing the describe output reports "Unchanged page".
• All 81 non-.fail doctype-tests and 998 bug-tests through both binaries: the only changed result is the new bug-test (fail → pass).
• Full go test ./..., go vet, gofmt and CI's doc checks pass with this batch's three branches merged onto main. Bug-test widget-action-1516-empty-call-args.mdl; finding recorded; mxcli syntax page.action and docs-site create-page updated.
• Not verified: opening the result in Studio Pro (the proof is identical BSON to the bracket-less form).

Noticed, not fixed

Whenever a specific page-body rule fails to match, the generic IDENTIFIER widget alternative plus an optional empty property list can silently re-read the input as unknown widgets — check without a project passes such pages, and only -p reports MDL-WIDGET25. Other near-miss spellings may hit the same trap.

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