// Test context expressions.
// Ref: false

---
// Test that context body is parsed as atomic expression.
#let c = [#context "hello".]
#test(c.children.first().func(), (context none).func())
#test(c.children.last(), [.])

---
// Test that manual construction is forbidden.
// Error: 2-25 cannot be constructed manually
#(context none).func()()

---
// Test that `here()` yields the context element's location.
#context test(query(here()).first().func(), (context none).func())

---
// Test whether context is retained in nested function.
#let translate(..args) = args.named().at(text.lang)
#set text(lang: "de")
#context test(translate(de: "Inhalt", en: "Contents"), "Inhalt")

---
// Test whether context is retained in built-in callback.
#set text(lang: "de")
#context test(
  ("en", "de", "fr").sorted(key: v => v != text.lang),
  ("de", "en", "fr"),
)

---
// Test `locate` + `here`.
#context test(here().position().y, 10pt)

---
// Test `locate`.
#v(10pt)
= Introduction <intro>
#context test(locate(<intro>).position().y, 20pt)

---
// Error: 10-25 label `<intro>` does not exist in the document
#context locate(<intro>)

---
= Introduction <intro>
= Introduction <intro>

// Error: 10-25 label `<intro>` occurs multiple times in the document
#context locate(<intro>)

---
#v(10pt)
= Introduction <intro>
#context test(locate(heading).position().y, 20pt)

---
// Error: 10-25 selector does not match any element
#context locate(heading)

---
= Introduction <intro>
= Introduction <intro>

// Error: 10-25 selector matches multiple elements
#context locate(heading)

---
// Test `counter`.
#let c = counter("heading")
#c.update(2)
#c.update(n => n + 2)
#context test(c.get(), (4,))
#c.update(n => n - 3)
#context test(c.at(here()), (1,))

---
// Test `state.at` outside of context.
// Error: 2-26 can only be used when context is known
// Hint: 2-26 try wrapping this in a `context` expression
// Hint: 2-26 the `context` expression should wrap everything that depends on this function
#state("key").at(<label>)

---
// Test `counter.at` outside of context.
// Error: 2-28 can only be used when context is known
// Hint: 2-28 try wrapping this in a `context` expression
// Hint: 2-28 the `context` expression should wrap everything that depends on this function
#counter("key").at(<label>)

---
// Test `measure`.
#let f(lo, hi) = context {
  let h = measure[Hello].height
  assert(h > lo)
  assert(h < hi)
}
#text(10pt, f(6pt, 8pt))
#text(20pt, f(13pt, 14pt))

---
// Test basic get rule.
#context test(text.lang, "en")
#set text(lang: "de")
#context test(text.lang, "de")
#text(lang: "es", context test(text.lang, "es"))

---
// Test folding.
#set rect(stroke: red)
#context {
  test(type(rect.stroke), stroke)
  test(rect.stroke.paint, red)
}
#[
  #set rect(stroke: 4pt)
  #context test(rect.stroke, 4pt + red)
]
#context test(rect.stroke, stroke(red))

---
// We have one collision: `figure.caption` could be both the element and a get
// rule for the `caption` field, which is settable. We always prefer the
// element. It's unfortunate, but probably nobody writes
// `set figure(caption: ..)` anyway.
#test(type(figure.caption), function)
#context test(type(figure.caption), function)

---
// Error: 10-31 Assertion failed: "en" != "de"
#context test(text.lang, "de")

---
// Error: 15-20 function `text` does not contain field `langs`
#context text.langs

---
// Error: 18-22 function `heading` does not contain field `body`
#context heading.body

---
// Error: 7-11 can only be used when context is known
// Hint: 7-11 try wrapping this in a `context` expression
// Hint: 7-11 the `context` expression should wrap everything that depends on this function
#text.lang

---
// Error: 7-12 function `text` does not contain field `langs`
#text.langs

---
// Error: 10-14 function `heading` does not contain field `body`
#heading.body

---
// Test that show rule establishes context.
#set heading(numbering: "1.")
#show heading: it => test(
  counter(heading).get(),
  (intro: (1,), back: (2,)).at(str(it.label)),
)

= Introduction <intro>
= Background <back>

---
// Test that show rule on non-locatable element allows `query`.
// Error: 18-47 Assertion failed: 2 != 3
#show emph: _ => test(query(heading).len(), 3)
#show strong: _ => test(query(heading).len(), 2)
= Introduction
= Background
*Hi* _there_

---
// Test error when captured variable is assigned to.
#let i = 0
// Error: 11-12 variables from outside the context expression are read-only and cannot be modified
#context (i = 1)