Grammar of "infix expression" does not allow `await`

[jansorg]

Location

https://docs.swift.org/swift-book/documentation/the-swift-programming-language/summaryofthegrammar/#Expressions
in section "Grammar of an infix expression"

Description

AFAIK this is valid (user's bug report for the JetBrains Swift plugin):

var device: Device?
device = try await viewModel.getDevice(id: id)

and if I'm not mistaken this part of the grammar is missing the await support:

infix-expression → infix-operator prefix-expression
infix-expression → assignment-operator try-operator? prefix-expression
infix-expression → conditional-operator try-operator? prefix-expression
infix-expression → type-casting-operator
infix-expressions → infix-expression infix-expressions?

Correction

Add the await as it's supported by this?

# Grammar of an expression
expression → try-operator? await-operator? prefix-expression infix-expressions?
expression-list → expression | expression , expression-list

[amartini51]

I think the change you're asking for is to add await to the grammar for prefix expressions?

The grammar already looks like what's in the Correction section above:

https://github.com/apple/swift-book/blob/main/TSPL.docc/ReferenceManual/Expressions.md?plain=1#L23

Grammar of an expression:

expression → try-operator? await-operator? prefix-expression infix-expressions?
expression-list → expression | expression , expression-list

Looking at the example in the linked issue:

device = try await viewModel.getDevice(id: id)

And walking through the grammar production:

• expression device = try await viewModel.getDevice(id: id)
  • prefix expression device
  • infix expression = try await viewModel.getDevice(id: id)
    • assignment operator operator =
    • try operator try
    • No grammar to generate await here
    • prefix-expression try await viewModel.getDevice(id: id)
      • (…)

So the correction would be as follows:

--- TSPL.docc/ReferenceManual/Expressions.md
+++ TSPL.docc/ReferenceManual/Expressions.md
@@ -327,8 +327,8 @@ ## Infix Expressions
 > Grammar of an infix expression:
 >
 > *infix-expression* → *infix-operator* *prefix-expression* \
-> *infix-expression* → *assignment-operator* *try-operator*_?_ *prefix-expression* \
-> *infix-expression* → *conditional-operator* *try-operator*_?_ *prefix-expression* \
+> *infix-expression* → *assignment-operator* *try-operator*_?_ *await-operator*_?_ *prefix-expression* \
+> *infix-expression* → *conditional-operator* *try-operator*_?_ *await-operator*_?_ *prefix-expression* \
 > *infix-expression* → *type-casting-operator* \
 > *infix-expressions* → *infix-expression* *infix-expressions*_?_

[jansorg]

Oh, sorry, my note in the section „Correction“ was misleading. I meant to add support for the await keyword to „infix-expression“ in the same way it‘s already supported by the grammar of „expression“. Your suggested change looks correct to me and is what I had in mind.

[amartini51]

@jansorg Thanks for the confirmation. I opened a PR to review and incorporate this fix.