Documentation
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Overview ¶
Package feelers renders the template language Atlas's forms already speak.
form-js's Text and HTML views evaluate their content with feelers (bpmn-io/feelers 3.1.0, bundled in api/web/vendor/form-js): text with {{ FEEL }} placeholders, {{#if FEEL}}…{{/if}} and {{#loop FEEL}}…{{/loop}} sections. A mail text is written in the same language (ADR-0487) and is rendered on the server, so this package implements it in Go: parsed, and every FEEL block compiled, once when the model is deployed (I5); rendered when the mail is sent.
It follows feelers wherever feelers decides, so a template reads the same in a form and in a mail:
- a placeholder renders FEEL's string() of its value, and null as nothing;
- {{#if}} renders its section when the value is truthy as JavaScript has it — false, null, 0 and "" are not, everything else is, an empty list included;
- {{#loop}} renders its section once per list element, not at all for null and once for any other single value. Inside, the element's fields are names of their own, `this` is the element and `parent` the enclosing context; the variables outside the loop are reached through `parent`, as in feelers;
- an opening tag swallows the line break directly after it, and so does a closing tag, which puts one back after a rendered section that did not end with one. That is what lets a section's tags stand on lines of their own.
Where feelers is lenient because a form must show whatever it is given, this package is strict when it compiles: an unclosed {{, a section without its end, an end without its section and FEEL that does not compile are refused when the model is deployed, rather than rendered as a warning sign in a mail that has already gone out. When it renders it is as lenient as the rest of Atlas's FEEL: a placeholder whose expression fails renders as nothing, and is reported.
A leading '=' is not this package's business. In Atlas it makes a whole value one FEEL expression, which the caller decides before it considers a template.
Index ¶
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
func IsTemplate ¶
IsTemplate reports whether src uses the template language at all — whether it has a {{ in it. A value without one is plain text and needs no template.
Types ¶
type CompileFunc ¶
CompileFunc compiles one FEEL block. The compiler hands in its deploy gate, so the FEEL in a template is held to the rules every other FEEL in a model is (ADR-0388).
type Error ¶
Error is a template that does not parse, or whose FEEL does not compile, with the place of the tag at fault: Line and Column count from 1, the column in characters.
type Problem ¶
Problem is a placeholder or section that rendered as nothing: its expression failed, or answered null where a value was wanted. A mail goes out regardless, as one with a failed FEEL field always has; a preview shows the problems beside the result.
type Scope ¶
type Scope interface {
// Lookup answers a variable's value, and whether it is set.
Lookup(name string) (expr.Value, bool)
// Names lists every variable. It is read only for `this` at the top level, which
// names the whole scope as one context, as it does in feelers.
Names() []string
}
Scope is what a template's names resolve against at its top level: the variables the task sees.
type Template ¶
type Template struct {
// contains filtered or unexported fields
}
Template is a parsed template with its FEEL compiled. It is immutable and safe for concurrent rendering, like the compiled process that holds it.
func Compile ¶
func Compile(src string, compile CompileFunc) (*Template, error)
Compile parses src and compiles each of its FEEL blocks with compile.
func (*Template) Render ¶
Render renders the template against scope. escape, when set, is applied to every value a placeholder inserts and never to the template's own text — an HTML body passes one, so a variable cannot add markup to it. Render does not fail: whatever cannot be evaluated renders as nothing and is listed in the problems.
Source Files