Introduce if/switch expressions #63022
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hamishknight
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This was referenced Jan 13, 2023
hamishknight
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Jan 13, 2023
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I'll try to take a look at this today! |
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Diff of changes modulo the rebase: https://github.com/apple/swift/compare/a6b33578a22e10de7ce272a60a1120f757f43f53..96da632832166b6d39b7f6b14f68560b50956210 |
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| if (!body || application.hadError) | ||
| return true; | ||
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| fn.setTypecheckedBody(castToStmt<BraceStmt>(body), | ||
| fn.hasSingleExpressionBody()); | ||
| fn.setTypecheckedBody(cast<BraceStmt>(body), fn.hasSingleExpressionBody()); |
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Hm, I think we have a bug here unrelated to your changes - if function/accessor/closure has been result builder transformed it would no longer be single-expression so we need to expand the check.
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Heh, good catch! I can file a bug if you want
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Let's do that so it doesn't get lost. I'll open a PR to fix that once your changes land.
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For a single expression closure, just use the expression as the body in the case where we're coercing to Void, as the return is already implied. This avoids crashing in `ClosureExpr::getSingleExpressionBody` with a double braced body. Surprisingly it seems nothing is currently calling `ClosureExpr::getSingleExpressionBody` after type-checking, so no test case, but later commits in this patch will exercise this case.
Split out brace element handling for a couple of walkers into a new function. The diff for this is best viewed without whitespace changes. This should be NFC.
Factor out some type-checking logic for ReturnStmt, including the conversion to FailStmt, into a request. We can then invoke this request from both the regular type-checking path, as well as during a pre-check of an expression.
Introduce SingleValueStmtExpr, which allows the embedding of a statement in an expression context. This then allows us to parse and type-check `if` and `switch` statements as expressions, gated behind the `IfSwitchExpression` experimental feature for now. In the future, SingleValueStmtExpr could also be used for e.g `do` expressions. For now, only single expression branches are supported for producing a value from an `if`/`switch` expression, and each branch is type-checked independently. A multi-statement branch may only appear if it ends with a `throw`, and it may not `break`, `continue`, or `return`. The placement of `if`/`switch` expressions is also currently limited by a syntactic use diagnostic. Currently they're only allowed in bindings, assignments, throws, and returns. But this could be lifted in the future if desired.
Look through `try`/`await` markers when looking for out of place if/switch expressions, and customize the effect checking diagnostic such that we error that `try`/`await` are redundant on `if`/`switch` expressions.
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Introduce SingleValueStmtExpr, which allows the embedding of a statement in an expression context. This then allows us to parse and type-check
ifandswitchstatements as expressions. In the future, SingleValueStmtExpr could also be used for e.gdoexpressions.For now, only single expression branches are supported for producing a value from an
if/switchexpression, and each branch is type-checked independently. A multi-statement branch may only appear if it ends with athrow, and it may notbreak,continue, orreturn.The placement of
if/switchexpressions is also currently limited by a syntactic use diagnostic. Currently they're only allowed in bindings, assignments, throws, and returns. But this could be lifted in the future if desired.