[6/n] rustc: transition HIR function bodies from Block to Expr. _This is part of a series ([prev](rust-lang#37408) | [next](rust-lang#37676)) of patches designed to rework rustc into an out-of-order on-demand pipeline model for both better feature support (e.g. [MIR-based](/~https://github.com/solson/miri) early constant evaluation) and incremental execution of compiler passes (e.g. type-checking), with beneficial consequences to IDE support as well. If any motivation is unclear, please ask for additional PR description clarifications or code comments._ <hr> The main change here is that functions and closures both use `Expr` instead of `Block` for their bodies. For closures this actually allows a honest representation of brace-less closure bodies, e.g. `|x| x + 1` is now distinguishable from `|x| { x + 1 }`, therefore this PR is `[syntax-breaking]` (cc @Manishearth). Using `Expr` allows more logic to be shared between constant bodies and function bodies, with some small such changes already part of this PR, and eventually easing rust-lang#35078 and per-body type tables. Incidentally, there used to be some corners cut here and there and as such I had to (re)write divergence tracking for type-checking so that it is capable of understanding basic structured control-flow: ``` rust fn a(x: bool) -> i32 { // match also works (as long as all arms diverge) if x { panic!("true") } else { return 1; } 0 // "unreachable expression" after this PR } ``` And since liveness' "not all control paths return a value" moved to type-checking we can have nice things: ``` rust // before & after: fn b() -> i32 { 0; } // help: consider removing this semicolon // only after this PR fn c() -> i32 { { 0; } } // help: consider removing this semicolon fn d() { let x: i32 = { 0; }; } // help: consider removing this semicolon fn e() { f({ 0; }); } // help: consider removing this semicolon ```

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Commits on Nov 9, 2016

Commits on Nov 10, 2016