Expressions and bindings

Bindings are where a Perspective view gets its data, and a broken binding fails quietly: the property shows null or an error overlay, and nothing is written to a log you would look at. iglint parses every expression with a parser tested against Ignition's own expression parser, and resolves every property reference against the view.

Expressions are checked wherever they occur: expression and expression-structure bindings, tag bindings in expression mode, query binding parameters, expression transforms, map transforms, session properties, expression tags, derived tags and bound tag and alarm properties.

All examples are invented; the messages are iglint's.

Syntax errors

if({view.custom.count} > 0, "some", )

view.json:31:70: BIND001 [error] Expression syntax error: unexpected `)`, expected an expression

The position points into the JSON string, at the offending character.

Unknown functions and wrong argument counts

The list of expression functions, and their parameters, was generated from a real 8.3 gateway.

toUpper({view.custom.name})
dateFormat(now(0))

view.json:53:32: BIND002 [error] Unknown expression function `toUpper` (did you mean `upper`?)
view.json:75:32: BIND003 [error] `dateFormat` does not accept 1 argument (parameters: date, pattern)

Functions of third-party modules can be declared with BIND002's extra-functions option.

Property references that do not resolve

A reference to a property that does not exist evaluates to null with a bad quality. BIND005 resolves every {...} reference and every property binding path: {this.custom.x}, {view.params.y}, {../Sibling.props.z}, {/root/A/B.custom.c} and the paths of property bindings.

"Area " + {view.custom.aera}

view.json:34:57: BIND005 [error] `view.custom.aera`: custom property `aera` is not defined
   = note: at root/Title.props.text@binding

The component and the first property segment are checked. Free-form keys below props (whatever a component accepts) are not, and neither are references built at run time.

Polling

now() without an argument polls every second, in the gateway, for every open session.

dateFormat(now(1000), "HH:mm:ss")

view.json:56:43: BIND004 [warning] `now` polls every 1000 ms, faster than the minimum of 10000 ms

The minimum is the rule's minimum-interval option (10,000 ms by default). runScript with a literal poll rate is checked the same way. Query, tag history and HTTP bindings that poll too often are PERF002's concern (see performance).

Tag bindings

An indirect tag binding replaces {name} placeholders in the tag path with the values of its references. When the two do not match, the path is never what the author meant:

{
  "type": "tag",
  "config": {
    "mode": "indirect",
    "tagPath": "[default]{area}/Speed",
    "references": { "line": "{view.custom.name}" }
  }
}

view.json:100:19: BIND006 [error] Reference `line` is not used by any `{line}` placeholder of the tag path
view.json:102:39: BIND006 [error] Placeholder `{area}` has no entry in `references`; it is never replaced

BIND007 reports a direct tag binding whose path contains {...}, which a direct binding never replaces. With TAG003 enabled, static tag paths are checked against the tags of the workspace (see References between resources).

Transforms

{
  "type": "property",
  "config": { "path": "view.custom.count" },
  "transforms": [
    { "type": "script", "code": "\tif value > 10:\n\t\treturn \"high\"" }
  ]
}

view.json:128:30: BIND009 [error] Script transform can finish without `return`; the property then becomes null

Script transforms are also linted as scripts, with the header def transform(self, value, quality, timestamp):, so every SCR rule applies to them. BIND010 reports a map transform that maps the same input twice.

Leftovers

Rule	Reports
BIND008	a binding disabled with enabled: false and left in place (info)
VIEW009	a property change script that is disabled but has code (info)
VIEW015	a custom property or view parameter that is never read anywhere it could be read: expressions, property bindings, scripts, and other views' parameters for input and output parameters
VIEW019	an output parameter that is never written (opt-in)
BIND011	obvious literal type errors such as "a" * 2 (opt-in)

VIEW015 is one of the rules ign-lint has too, but iglint matches references exactly ({view.custom.foobar} is not a use of foo), treats script assignments as writes, not reads, and stays silent when a script uses a property container in a way it cannot follow. Its fix removes the property and its propConfig entry.