paulk-asert opened a new pull request, #2932:
URL: https://github.com/apache/groovy/pull/2932
…ement
GROOVY-12399 restored Java's rule that position, not arm shape, decides
whether a switch produces a value, but carved out a third case: a switch in
implicit-return position stayed an expression that yielded null when unmatched,
so that a method whose body is a bare switch kept its 5.x value. That carve-out
cost more than it bought.
It made one piece of syntax mean two things. Under @CompileStatic a `case
label` with a declared-Object label resolved statically in that position and
dynamically once any statement followed the switch, so adding a trailing line
changed how labels matched. It also required about 110 lines in AstBuilder to
recognise implicit-return position, duplicating what ReturnAdder already knows,
on a different tree.
The carve-out existed because a SwitchStatement was a second-class citizen
in static compilation, not because the semantics needed it. GROOVY-12405 gave
statements the same jump-table dispatch and GROOVY-12406 the same
duplicate-label diagnostic, so nothing is left to protect. A switch whose value
is not used is now a statement wherever it appears, and Groovy's implicit
return does to it what it does to any other statement, via ReturnAdder.
Three behaviours move, each toward consistency:
- A primitive-returning method whose bare switch matches nothing now yields
the type's default, as `int f(int i) { if (i == 1) return 1 }` and the colon
form always have. The arrow form was the only shape in the language that threw
there, GroovyCastException dynamically and NullPointerException when statically
compiled.
- `case label` in that position matches as it does when the value is
discarded, and as it did in 5.x.
- The node is a SwitchStatement, which is visible to AST transforms.
COMPATIBILITY.md already warns that audience about GROOVY-12255.
Deleted: the UNMATCHED_YIELDS_NULL marker and its three readers, and
isImplicitReturnPosition, returnsValue, isLastStatement and isLenientPosition
from AstBuilder. isSwitchValueUsed keeps the recursion added for nested arrow
arms, since an arm of a switch that is itself a statement still produces
nothing.
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