This can almost be fully disabled, as it no longer breaks retrieving a
backtrace on OS X as verified by @alexcrichton. However, it still
breaks retrieving the values of parameters. This should be fixable in
the future via a proper location list...
Closes#7477
The general consensus is that we want to move away from conditions for I/O, and I propose a two-step plan for doing so:
1. Warn about unused `Result` types. When all of I/O returns `Result`, it will require you inspect the return value for an error *only if* you have a result you want to look at. By default, for things like `write` returning `Result<(), Error>`, these will all go silently ignored. This lint will prevent blind ignorance of these return values, letting you know that there's something you should do about them.
2. Implement a `try!` macro:
```
macro_rules! try( ($e:expr) => (match $e { Ok(e) => e, Err(e) => return Err(e) }) )
```
With these two tools combined, I feel that we get almost all the benefits of conditions. The first step (the lint) is a sanity check that you're not ignoring return values at callsites. The second step is to provide a convenience method of returning early out of a sequence of computations. After thinking about this for awhile, I don't think that we need the so-called "do-notation" in the compiler itself because I think it's just *too* specialized. Additionally, the `try!` macro is super lightweight, easy to understand, and works almost everywhere. As soon as you want to do something more fancy, my answer is "use match".
Basically, with these two tools in action, I would be comfortable removing conditions. What do others think about this strategy?
----
This PR specifically implements the `unused_result` lint. I actually added two lints, `unused_result` and `unused_must_use`, and the first commit has the rationale for why `unused_result` is turned off by default.
In line with the dissolution of libextra - #8784 - this moves arena and glob into
their own respective modules. Updates .gitignore with the entries
doc/{arena,glob} in accordance.
In line with the dissolution of libextra - #8784 - moves arena to its own library libarena.
Changes based on PR #11787. Updates .gitignore to ignore doc/arena.
I attempted to implement the lint in two steps. My first attempt was a
default-warn lint about *all* unused results. While this attempt did indeed find
many possible bugs, I felt that the false-positive rate was too high to be
turned on by default for all of Rust.
My second attempt was to make unused-result a default-allow lint, but allow
certain types to opt-in to the notion of "you must use this". For example, the
Result type is now flagged with #[must_use]. This lint about "must use" types is
warn by default (it's different from unused-result).
The unused_must_use lint had a 100% hit rate in the compiler, but there's not
that many places that return Result right now. I believe that this lint is a
crucial step towards moving away from conditions for I/O (because all I/O will
return Result by default). I'm worried that this lint is a little too specific
to Result itself, but I believe that the false positive rate for the
unused_result lint is too high to make it useful when turned on by default.
Refactored the file quite a bit, I can add unit tests if desired. There's a few changes from the previous version's behavior:
- destination directory will be created if it doesn't exist
- strings and file is written as unicode
I have a few questions, but will ask them in #11362.
Set "Dwarf Version" to 2 on OS X to avoid toolchain incompatibility, and
set "Debug Info Version" to prevent debug info from being stripped from
bitcode.
Fixes#11352.
Set "Dwarf Version" to 2 on OS X to avoid toolchain incompatibility, and
set "Debug Info Version" to prevent debug info from being stripped from
bitcode.
Fixes#11352.
cc #7621.
See the commit message. I'm not sure if we should merge this now, or wait until we can write `Clone::clone(x)` which will directly solve the above issue with perfect error messages.
This unfortunately changes an error like
error: mismatched types: expected `&&NotClone` but found `&NotClone`
into
error: type `NotClone` does not implement any method in scope named `clone`
In two ways:
- for a plain `fail!(a)` we make the generic part of `begin_unwind` as small as possible (makes `fn main() { fail!() }` compile 2-3x faster, due to less monomorphisation bloat)
- for `fail!("format {}", "string")`, we avoid touching the generics completely by doing the formatting in a specialised function, which (with optimisations) saves a function call at the call-site of `fail!`. (This one has significantly less benefit than the first.)
Non-exhaustive change list:
* `self` is now present in argument lists (modulo type-checking code I don't trust myself to refactor)
* methods have the same calling convention as bare functions (including the self argument)
* the env param is gone from all bare functions (and methods), only used by closures and `proc`s
* bare functions can only be coerced to closures and `proc`s if they are statically resolved, as they now require creating a wrapper specific to that function, to avoid indirect wrappers (equivalent to `impl<..Args, Ret> Fn<..Args, Ret> for fn(..Args) -> Ret`) that might not be optimizable by LLVM and don't work for `proc`s
* refactored some `trans::closure` code, leading to the removal of `trans::glue::make_free_glue` and `ty_opaque_closure_ptr`
Johannes Muenzel