fix(grammar): an empty argument list on a page action or flow data source means no arguments

.claude/skills/fix-issue/findings/mdl-grammar/2026-10-27-widget-action-empty-argument-list-syntax-error.json

@@ -0,0 +1 @@
+{"area": "mdl/grammar", "date": "2026-10-27", "symptom": "ako/mxcli#1516 (mendixlabs/mxcli#1606): `actionbutton b (Caption: 'Ping', Action: call microflow M.Ping())` failed `mxcli check` with `mismatched input ')' expecting the start of a statement`, while `call microflow M.Ping();` parses in a flow body and the widget action parsed without the brackets. Same error for call nanoflow, show page, the deprecated microflow/nanoflow/show_page spellings, a microflow or nanoflow DataSource, OnClick, OnChange, a pluggable widget's action property, `alter page set Action`/`set DataSource`, and a navigation or menu-document item's OnClick. `use fragment Hdr()` was worse: no error at all without a project", "cause": "microflowArgsV3 (MDLPage.g4) required at least one argument, `LPAREN microflowArgV3 (COMMA microflowArgV3)* RPAREN`, and every one of those sites reaches it through actionExprV3 or dataSourceExprV3. The optional rule failed on `( )`, the widget's property list then met `(` and recovery blamed the `)`. fragmentArgs had the same shape, but there the page body's generic widget alternative (`widgetTypeV3` ends in IDENTIFIER, and widgetPropertiesV3 MAY be empty) re-read `use fragment Hdr()` as a widget of type `use` named `fragment` plus a widget of type `Hdr` with `()` as its properties, so check without -p passed and check -p said '`use` is not a widget in this project' (MDL-WIDGET25)", "file": "mdl/grammar/domains/MDLPage.g4 (microflowArgsV3, fragmentArgs)", "fix": "Both rules take an optional list inside the brackets, like workflowCallArguments and the flow-body callArgumentList already did. No visitor change: buildMicroflowArgsV3 and buildFragmentArgs return nil for no children, so `X()` builds the statement `X` builds. Purely additive (a refused script now parses), so no mdl-version gate. describe still writes no brackets", "test": "mdl/visitor/visitor_empty_call_args_test.go: 23 sites, each X() vs X compared as whole statements plus deprecation codes, with a non-empty argument list as the control that must differ. Reverting the grammar (patch out, make grammar) fails all 23: 22 as parse errors and use fragment on statement equality, since it parsed as two widgets. Real 11.13.0 app (mdl-examples/bug-tests/widget-action-1516-empty-call-args.mdl): a page written with () and its bracket-less twin store identical BSON once $ID and the page name are set aside, describe identically, describe -> exec reports Unchanged, mx check 0 errors", "insight": "One shared rule carried eight alternatives (six actions, two data sources) into every site that takes an action or a data source, which is the argument for auditing by rule rather than by the reported spelling: grep for the rule name, not the keyword. Compare WHOLE statements between X() and X, not the Args field: an empty-but-present mapping list, or an alternative that silently matched something else, both show up there, and a control (a real argument list must change the statement) proves the comparison can see a difference. A rule that cannot match does not always produce a parse error: when a generic fall-back alternative exists (here an unknown widget type with an optional empty property list) the input is re-read as something else and `check` without a project passes, so a site that 'parses' at baseline still needs the AST checked. `use building block X()` and `snippetcall (Params: ())` stay errors on purpose: they are an override list and a property map, not an argument list, and the messages already name what is expected", "refs": ["ako/mxcli#1516", "mendixlabs/mxcli#1606"], "rules": ["MDL-WIDGET25"]}

cmd/mxcli/syntax/features_page.go

@@ -293,7 +293,7 @@ LIST IMPACT OF htmlelement;
 			"confirmation", "confirm", "are you sure", "progress bar", "progress message",
 			"disabled during execution", "disabled during action", "asynchronous", "form validations",
 		},
-		Syntax:  "Action: NOTHING                      -- deliberately no action (Forms$NoAction)\nAction: SAVE CHANGES\nAction: SAVE CHANGES CLOSE PAGE      -- save, then close the pop-up\nAction: CANCEL CHANGES\nAction: CANCEL CHANGES CLOSE PAGE\nAction: CLOSE PAGE\nAction: DELETE\nAction: DELETE CLOSE PAGE\nAction: CALL NANOFLOW Module.NF\nAction: CALL NANOFLOW Module.NF(Param = $val)\nAction: OPEN LINK 'https://example.com'\nAction: OPEN LINK $currentObject/URL  -- address read from an attribute\nAction: SIGN OUT\nAction: COMPLETE TASK 'OutcomeName'\nAction: SHOW PAGE Module.Page\nAction: SHOW PAGE Module.Page(Param = $currentObject)\nAction: CALL MICROFLOW Module.MF\nAction: CALL MICROFLOW Module.MF(Param = $val)\nAction: CREATE OBJECT Module.Entity THEN SHOW PAGE Module.Page\n\nThe list above is exhaustive. Anything else in an action slot is an\nERROR: `Action: OPEN LINK` without a URL or `Action: SHOW PAGE` without a\npage is a syntax error, and a value that is not an action at all\n(or a snake-case keyword short its argument) is MDL-WIDGET28.\nSuch a widget used to be written with NO action at all and rendered as a\ndead control, with check, exec and mxbuild all clean, because a\nno-action widget is legal Mendix (mendixlabs/mxcli#1062). Write NOTHING\nwhen a control really is meant to be inert.\n\nThe actions are the words a microflow uses (R8). The snake-case spellings\n(SAVE_CHANGES, SHOW_PAGE, CLOSE_PAGE, DELETE_OBJECT, OPEN_LINK, SIGN_OUT, ...)\nand a flow call without CALL still parse, but are deprecated (MDL-DEPR020);\n`mxcli fmt --upgrade` rewrites them.\n\nThe same forms serve `OnClick:` (an alias of `Action:`) and `OnChange:`.\n\nSETTINGS. Any action but NOTHING takes a `with ( … )` list of the\nsettings Studio Pro shows under the event (ako/mxcli#721):\n\n  DisabledDuringExecution: true|false  -- every action; default true\n  ProgressBar: None|NonBlocking|Blocking  -- flow calls; default None\n  ProgressMessage: 'text'                -- flow calls\n  Confirmation: 'question'               -- flow calls: ask before running\n  ProceedCaption: 'text', CancelCaption: 'text'  -- its buttons; default Proceed / Cancel\n  Asynchronous: true|false               -- call microflow only; default false\n  FormValidations: All|Widget|None       -- call microflow only; default All\n\nAction: CALL MICROFLOW M.Delete(Order = $currentObject) with (\n  ProgressBar: Blocking, ProgressMessage: 'Deleting…',\n  Confirmation: 'Delete this order?', ProceedCaption: 'Delete', CancelCaption: 'Keep')\n\nA setting left out keeps its default. DESCRIBE prints only the settings\nthat differ from it. An unknown key, or one the action does not have, is an\nerror. For CREATE OBJECT … THEN SHOW PAGE …, the list goes at the end and\nbelongs to the create.\n\nRETURN VALUE MAPPINGS. A flow call can map what the flow returns back onto\nthe page -- Studio Pro's \"Return value mappings\" (Mendix 11.5). The list\ngoes after the arguments and before `with ( … )`, target = source:\n\nAction: CALL MICROFLOW M.ACT_Vehicle_Get returns (\n  Brand = $ActionReturnValue/Brand,     -- an attribute of the returned object\n  $stringResult = $ActionReturnValue,   -- the return value itself\n  Brand = 'Demo brand')                 -- any expression\n\nA bare target is an attribute of the enclosing data container's object;\n`$name` is a page variable. $ActionReturnValue/Attr needs a flow that\nreturns an object. A mapping into an attribute needs Mendix 11.15: mx\n11.13 and 11.14 report CE7006 on it. Leave the list out and the call maps\nnothing; DESCRIBE prints the stored mappings, and re-running a statement\nwithout them removes them (ako/mxcli#977).\n\nA microflow or nanoflow action is a CALL: it needs an argument for every\nparameter the flow declares, or Mendix rejects the page with CE1571. The\nargument list is the same on every widget that takes an action -- a\nCONTAINER (which is clickable) as much as an ACTIONBUTTON. An enclosing\ndata container of the right type supplies it without an argument; a data\ngrid's CONTROL BAR does not, because it is not row-scoped -- pass the\ngrid's selection there (`$dgOrders`).\n\nA SHOW PAGE argument must be the enclosing widget's context object --\neither $currentObject or the name of the variable the enclosing data\nwidget is bound to. Mendix infers it from that widget, so naming any\nother variable is refused (MDL-PAGEARG01); call a microflow instead.\nThe exception is a parameter of the page or snippet itself: it is bound\nby name (Studio Pro stores an explicit mapping), so `(Item = $Item)` works\nanywhere, outside every data widget too (mendixlabs/mxcli#1403).\nOutside any data widget there is no context object to infer, so such a\nbutton takes no OTHER argument -- not $currentObject, not a literal.\nmxcli used to drop it in silence and mxbuild then reported CE1571 per\nparameter of the target page (mendixlabs/mxcli#1029). Route that\nnavigation through a microflow.\n\nOPEN LINK takes a web address, stored as a Forms$StaticOrDynamicString:\neither a literal, or $currentObject/Attr to read it from an attribute of\nthe enclosing data container's object at runtime (Studio Pro's \"Address:\nattribute\"). An address over an association path is not supported yet.\n\nButton styles: Default, Primary, Success, Info, Warning, Danger\n\nMendix has THREE icon elements and the keyword picks which one:\n\nIcon: 'Atlas_Core.Atlas_Filled.pencil'   -- an icon collection\nIcon: image MyModule.Images.logo         -- an IMAGE collection\nIcon: glyph 57377                        -- a font code point\n\nThe bare form is the icon-collection icon and any collection in the\nproject works, third-party ones included. The image form points into a\ndifferent document, and is spelled the same way apart from the keyword\n-- write it without `image` and mxcli stores a custom-icon reference,\nwhich fails the build with CE1613 (mendixlabs/mxcli#1059).\n`mxcli check -p … --references` resolves each kind against its own\ncollection and names the remedy when the kind is wrong.\n\nA glyph carries a code and no name. Codes are sparse, and an undefined\none fails only at `mxbuild --target=deploy`, naming the PAGE rather\nthan the icon -- so MDL078 refuses it (an error) against the font's own\ntable, naming the defined glyphs either side of the code.\nList them with `list glyphs`.\n\nA name may be quoted or bare; a hyphenated segment is double-quoted on\nits own: Atlas_Core.Atlas.\"align-center\".\n\nUse `linkbutton` instead of `actionbutton` for link render mode (same properties).",
+		Syntax:  "Action: NOTHING                      -- deliberately no action (Forms$NoAction)\nAction: SAVE CHANGES\nAction: SAVE CHANGES CLOSE PAGE      -- save, then close the pop-up\nAction: CANCEL CHANGES\nAction: CANCEL CHANGES CLOSE PAGE\nAction: CLOSE PAGE\nAction: DELETE\nAction: DELETE CLOSE PAGE\nAction: CALL NANOFLOW Module.NF\nAction: CALL NANOFLOW Module.NF(Param = $val)\nAction: OPEN LINK 'https://example.com'\nAction: OPEN LINK $currentObject/URL  -- address read from an attribute\nAction: SIGN OUT\nAction: COMPLETE TASK 'OutcomeName'\nAction: SHOW PAGE Module.Page\nAction: SHOW PAGE Module.Page(Param = $currentObject)\nAction: CALL MICROFLOW Module.MF\nAction: CALL MICROFLOW Module.MF(Param = $val)\nAction: CREATE OBJECT Module.Entity THEN SHOW PAGE Module.Page\n\nThe list above is exhaustive. Anything else in an action slot is an\nERROR: `Action: OPEN LINK` without a URL or `Action: SHOW PAGE` without a\npage is a syntax error, and a value that is not an action at all\n(or a snake-case keyword short its argument) is MDL-WIDGET28.\nSuch a widget used to be written with NO action at all and rendered as a\ndead control, with check, exec and mxbuild all clean, because a\nno-action widget is legal Mendix (mendixlabs/mxcli#1062). Write NOTHING\nwhen a control really is meant to be inert.\n\nThe actions are the words a microflow uses (R8). The snake-case spellings\n(SAVE_CHANGES, SHOW_PAGE, CLOSE_PAGE, DELETE_OBJECT, OPEN_LINK, SIGN_OUT, ...)\nand a flow call without CALL still parse, but are deprecated (MDL-DEPR020);\n`mxcli fmt --upgrade` rewrites them.\n\nThe same forms serve `OnClick:` (an alias of `Action:`) and `OnChange:`.\n\nA call to a flow or page with no parameters may end in an empty `()`,\nas a flow body writes it. It stores the same action as no list at all,\nand DESCRIBE leaves it out (ako/mxcli#1516).\n\nSETTINGS. Any action but NOTHING takes a `with ( … )` list of the\nsettings Studio Pro shows under the event (ako/mxcli#721):\n\n  DisabledDuringExecution: true|false  -- every action; default true\n  ProgressBar: None|NonBlocking|Blocking  -- flow calls; default None\n  ProgressMessage: 'text'                -- flow calls\n  Confirmation: 'question'               -- flow calls: ask before running\n  ProceedCaption: 'text', CancelCaption: 'text'  -- its buttons; default Proceed / Cancel\n  Asynchronous: true|false               -- call microflow only; default false\n  FormValidations: All|Widget|None       -- call microflow only; default All\n\nAction: CALL MICROFLOW M.Delete(Order = $currentObject) with (\n  ProgressBar: Blocking, ProgressMessage: 'Deleting…',\n  Confirmation: 'Delete this order?', ProceedCaption: 'Delete', CancelCaption: 'Keep')\n\nA setting left out keeps its default. DESCRIBE prints only the settings\nthat differ from it. An unknown key, or one the action does not have, is an\nerror. For CREATE OBJECT … THEN SHOW PAGE …, the list goes at the end and\nbelongs to the create.\n\nRETURN VALUE MAPPINGS. A flow call can map what the flow returns back onto\nthe page -- Studio Pro's \"Return value mappings\" (Mendix 11.5). The list\ngoes after the arguments and before `with ( … )`, target = source:\n\nAction: CALL MICROFLOW M.ACT_Vehicle_Get returns (\n  Brand = $ActionReturnValue/Brand,     -- an attribute of the returned object\n  $stringResult = $ActionReturnValue,   -- the return value itself\n  Brand = 'Demo brand')                 -- any expression\n\nA bare target is an attribute of the enclosing data container's object;\n`$name` is a page variable. $ActionReturnValue/Attr needs a flow that\nreturns an object. A mapping into an attribute needs Mendix 11.15: mx\n11.13 and 11.14 report CE7006 on it. Leave the list out and the call maps\nnothing; DESCRIBE prints the stored mappings, and re-running a statement\nwithout them removes them (ako/mxcli#977).\n\nA microflow or nanoflow action is a CALL: it needs an argument for every\nparameter the flow declares, or Mendix rejects the page with CE1571. The\nargument list is the same on every widget that takes an action -- a\nCONTAINER (which is clickable) as much as an ACTIONBUTTON. An enclosing\ndata container of the right type supplies it without an argument; a data\ngrid's CONTROL BAR does not, because it is not row-scoped -- pass the\ngrid's selection there (`$dgOrders`).\n\nA SHOW PAGE argument must be the enclosing widget's context object --\neither $currentObject or the name of the variable the enclosing data\nwidget is bound to. Mendix infers it from that widget, so naming any\nother variable is refused (MDL-PAGEARG01); call a microflow instead.\nThe exception is a parameter of the page or snippet itself: it is bound\nby name (Studio Pro stores an explicit mapping), so `(Item = $Item)` works\nanywhere, outside every data widget too (mendixlabs/mxcli#1403).\nOutside any data widget there is no context object to infer, so such a\nbutton takes no OTHER argument -- not $currentObject, not a literal.\nmxcli used to drop it in silence and mxbuild then reported CE1571 per\nparameter of the target page (mendixlabs/mxcli#1029). Route that\nnavigation through a microflow.\n\nOPEN LINK takes a web address, stored as a Forms$StaticOrDynamicString:\neither a literal, or $currentObject/Attr to read it from an attribute of\nthe enclosing data container's object at runtime (Studio Pro's \"Address:\nattribute\"). An address over an association path is not supported yet.\n\nButton styles: Default, Primary, Success, Info, Warning, Danger\n\nMendix has THREE icon elements and the keyword picks which one:\n\nIcon: 'Atlas_Core.Atlas_Filled.pencil'   -- an icon collection\nIcon: image MyModule.Images.logo         -- an IMAGE collection\nIcon: glyph 57377                        -- a font code point\n\nThe bare form is the icon-collection icon and any collection in the\nproject works, third-party ones included. The image form points into a\ndifferent document, and is spelled the same way apart from the keyword\n-- write it without `image` and mxcli stores a custom-icon reference,\nwhich fails the build with CE1613 (mendixlabs/mxcli#1059).\n`mxcli check -p … --references` resolves each kind against its own\ncollection and names the remedy when the kind is wrong.\n\nA glyph carries a code and no name. Codes are sparse, and an undefined\none fails only at `mxbuild --target=deploy`, naming the PAGE rather\nthan the icon -- so MDL078 refuses it (an error) against the font's own\ntable, naming the defined glyphs either side of the code.\nList them with `list glyphs`.\n\nA name may be quoted or bare; a hyphenated segment is double-quoted on\nits own: Atlas_Core.Atlas.\"align-center\".\n\nUse `linkbutton` instead of `actionbutton` for link render mode (same properties).",
 		Example: "ACTIONBUTTON btnSave (Caption: 'Save', Action: SAVE CHANGES, ButtonStyle: Primary)\nACTIONBUTTON btnEdit (Caption: 'Edit',\n  Action: SHOW PAGE Module.EditPage(Item = $currentObject))\nLINKBUTTON btnDelete (Caption: 'Delete', Action: DELETE,\n  Icon: 'Atlas_Core.Atlas_Filled.pencil')\n\n-- A clickable CONTAINER in a data grid's control bar, calling a nanoflow\n-- with the grid's selection as its argument.\nDATAGRID dgOrders (DataSource: DATABASE FROM Sales.Order, Selection: Single) {\n  COLUMN (Attribute: Number, Caption: 'Order #')\n  CONTROLBAR {\n    CONTAINER cShip (Class: 'command',\n      Action: CALL NANOFLOW Sales.ACT_Ship(Order = $dgOrders)) {\n      ACTIONBUTTON btnShip (Caption: 'Ship')\n    }\n  }\n}",
 		SeeAlso: []string{"page.widgets"},
 	})

cmd/mxcli/syntax/retired_spellings_test.go

@@ -25,8 +25,10 @@ func TestSyntaxDocs_NoRetiredSpellings(t *testing.T) {
 			"the parser rejects it: \"'Binds:' is no longer supported, use 'Attribute:' instead\"",
 		},
 		{
+			// Not retired since ako/mxcli#1516 — `()` parses and stores nothing —
+			// but the reference shows the form DESCRIBE writes.
 			"MICROFLOW Module.MF()",
-			"a zero-argument microflow DATASOURCE takes no parentheses (unlike RETRIEVE/CALL, where they are normal)",
+			"the reference shows a zero-argument call or data source the way DESCRIBE writes it, without parentheses; `()` is accepted and means the same (ako/mxcli#1516)",
 		},
 	}
 

docs-site/src/reference/page/create-page.md

@@ -141,6 +141,12 @@ mistake.
 
 The same values serve `OnClick:` (an alias of `Action:`) and `OnChange:`.
 
+A flow or page that takes no parameters may be called with an empty argument
+list, as a flow body writes it: `Action: CALL MICROFLOW Module.Name()` stores
+exactly what `Action: CALL MICROFLOW Module.Name` stores, and `DESCRIBE` writes
+it without the brackets. The same holds for a microflow or nanoflow data source
+and for `USE FRAGMENT Name()`.
+
 #### Action settings
 
 Any action but `NOTHING` takes a `with ( … )` list of the settings Studio Pro