#1589: Add error message for not emitting switch. #3556
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dottybot
reviewed
Nov 26, 2017
vitorsvieira
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senia-psm
reviewed
Nov 26, 2017
| |val number = (middle: @switch) match { | ||
| | case 'a' => 1 | ||
| | case 'm' => 13 | ||
| | case last => 26 //a non-literal may prevent switch generation: this would not compile. |
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case _ is unreachable. You might want to either replace
case last => ...
with
case `last` => ...
or rename last to Last
allanrenucci
suggested changes
Nov 26, 2017
| case class UnableToEmitSwitch()(implicit ctx: Context) | ||
| extends Message(UnableToEmitSwitchID) { | ||
| val kind = "Syntax" | ||
| val msg = hl"""Could not emit switch for ${"@switch"} annotated match""" |
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No need for triple quotes
| | case 'm' => 13 | ||
| | case Last => 26 //a non-literal may prevent switch generation: this would not compile. | ||
| | case _ => 0 | ||
| |}""".stripMargin |
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A more complete example:
val ConstantB = 'B'
final val ConstantC = 'C'
def tokenMe(ch: Char) = (ch: @switch) match {
case '\t' | '\n' => 1
case 'A' => 2
case ConstantB => 3 // a non-literal may prevent switch generation: this would not compile
case ConstantC => 4 // a constant value is allowed
case _ => 5
}There was a problem hiding this comment.
Awesome! Updated.
| |-The matched value is a known integer or types implicitly convertible to integer. | ||
| |-The matched expression only matches literal values, without type checks, if statements, or extractors. | ||
| |-The expression have its value available at compile time. | ||
| |-There are more than two case statements.""" |
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If annotated with ${"@switch"}, the compiler will verify that the match has been compiled to a
tableswitch or lookupswitch and issue an error if it instead compiles into a series of conditional
expressions. Example usage:
$codeExample
The compiler will not apply the optimisation if:
- the matched value is not of type ${"Int"}, ${"Byte"}, ${"Short"} or ${"Char"}
- the matched value is not a constant literal
- there are less than three cases
|
Please change the commit message to |
allanrenucci
approved these changes
Nov 27, 2017
|
Cool! 👍 |
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Regarding #1589, this PR addresses "could not emit switch" (PatternMatcher.911).
Noticed that
ctx.warningwas not propagating the error messages during tests.@smarter Suggested to refactor
checkMessagesAfterin a way that errors and warning messages are reported.Would it be something like below?
I'd be more than happy to contribute!