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[SR-8504] Confusing error message for '<' comparison after 'as' cast #51024

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huonw mannequin opened this issue Aug 10, 2018 · 1 comment
Open

[SR-8504] Confusing error message for '<' comparison after 'as' cast #51024

huonw mannequin opened this issue Aug 10, 2018 · 1 comment
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself diagnostics QoI Bug: Diagnostics Quality of Implementation parser Area → compiler: The legacy C++ parser

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@huonw
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Mannequin

huonw mannequin commented Aug 10, 2018

Previous ID SR-8504
Radar rdar://problem/27751587
Original Reporter @huonw
Type Bug
Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug, DiagnosticsQoI, Parser
Assignee None
Priority Medium

md5: 16c5ef9515b96271e36bca5ac9b9e349

Issue Description:

The following code is invalid, as the `as? ...` starts parsing a following type, and Int < ... looks like the start of a generic type.

let x: Any = 0
if x as? Int < Int(0) {}

There's a huge spew of error messages:

lessthan.swift:2:19: error: expected '>' to complete generic argument list
if x as? Int < Int(0) {}
                  ^
lessthan.swift:2:14: note: to match this opening '<'
if x as? Int < Int(0) {}
             ^
lessthan.swift:2:23: error: top-level statement cannot begin with a closure expression
if x as? Int < Int(0) {}
                      ^
lessthan.swift:2:23: error: closure expression is unused
if x as? Int < Int(0) {}
                      ^
lessthan.swift:2:23: note: did you mean to use a 'do' statement?
if x as? Int < Int(0) {}
                      ^
                      do

The fix for the syntax error is separating the as ... from the comparison, e.g. (x as? Int) < Int(0))
@typesanitizer
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@swift-ci create

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself diagnostics QoI Bug: Diagnostics Quality of Implementation parser Area → compiler: The legacy C++ parser
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