cantFail is the moral equivalent of an assertion that the wrapped call must
return a success value. This patch allows clients to include an associated
error message (the same way they would for an assertion for llvm_unreachable).
If the error message is not specified it will default to: "Failure value
returned from cantFail wrapped call".
llvm-svn: 312066
handleExpected is similar to handleErrors, but takes an Expected<T> as its first
input value and a fallback functor as its second, followed by an arbitary list
of error handlers (equivalent to the handler list of handleErrors). If the first
input value is a success value then it is returned from handleErrors
unmodified. Otherwise the contained error(s) are passed to handleErrors, along
with the handlers. If handleErrors returns success (indicating that all errors
have been handled) then handleExpected runs the fallback functor and returns its
result. If handleErrors returns a failure value then the failure value is
returned and the fallback functor is never run.
This simplifies the process of re-trying operations that return Expected values.
Without this utility such retry logic is cumbersome as the internal Error must
be explicitly extracted from the Expected value, inspected to see if its
handleable and then consumed:
enum FooStrategy { Aggressive, Conservative };
Expected<Foo> tryFoo(FooStrategy S);
Expected<Foo> Result;
(void)!!Result; // "Check" Result so that it can be safely overwritten.
if (auto ValOrErr = tryFoo(Aggressive))
Result = std::move(ValOrErr);
else {
auto Err = ValOrErr.takeError();
if (Err.isA<HandleableError>()) {
consumeError(std::move(Err));
Result = tryFoo(Conservative);
} else
return std::move(Err);
}
with handleExpected, this can be re-written as:
auto Result =
handleExpected(
tryFoo(Aggressive),
[]() { return tryFoo(Conservative); },
[](HandleableError&) { /* discard to handle */ });
llvm-svn: 311870
Summary:
If assertions are disabled, but LLVM_ABI_BREAKING_CHANGES is enabled,
this will cause an issue with an unchecked Success. Switching to
consumeError() is the correct way to bypass the check. This patch also
includes disabling 2 tests that can't work without assertions enabled,
since llvm_unreachable() with NDEBUG won't crash.
Reviewers: llvm-commits, lhames
Reviewed By: lhames
Subscribers: lhames, pirama
Differential Revision: https://reviews.llvm.org/D36729
llvm-svn: 311739
This just switches handleAllErrors from using custom assertions that all errors
have been handled to using cantFail. This change involves moving some of the
class and function definitions around though.
llvm-svn: 311631
fallible functions.
Some fallible functions (those returning Error or Expected<T>) may only fail
for a subset of their inputs. For example, a "safe" square root function will
succeed for all finite positive inputs:
Expected<double> safeSqrt(double d) {
if (d < 0 && !isnan(d) && !isinf(d))
return make_error<...>("Cannot sqrt -ve values, nans or infs");
return sqrt(d);
}
At a safe callsite for such a function, checking the error return value is
redundant:
if (auto ValOrErr = safeSqrt(42.0)) {
// use *ValOrErr.
} else
llvm_unreachable("safeSqrt should always succeed for +ve values");
The cantFail function wraps this check and extracts the contained value,
simplifying control flow:
double Result = cantFail(safeSqrt(42.0));
This function should be used with care: it is a programmatic error to wrap a
call with cantFail if it can in fact fail. For debug builds this will
result in llvm_unreachable being called. For release builds the behavior is
undefined.
Use of this function is likely to be rare in library code, but more common
for tool and unit-test code where inputs and mock functions may be known to be
safe.
llvm-svn: 296384
This is consistent with the header (after r288087) and fixes the
test for the configuration:
-DLLVM_ENABLE_ASSERTIONS=ON -DLLVM_ABI_BREAKING_CHECKS=FORCE_OFF
llvm-svn: 288196
This is forcing to use Error::success(), which is in a wide majority
of cases a lot more readable.
Differential Revision: https://reviews.llvm.org/D26481
llvm-svn: 286561
This allows ErrorAsOutParameter to work better with "optional" errors. For
example, consider a function where for certain input values it is known that
the function can't fail. This can now be written as:
Result foo(Arg X, Error *Err) {
ErrorAsOutParameter EAO(Err);
if (<Error Condition>) {
if (Err)
*Err = <report error>;
else
llvm_unreachable("Unexpected failure!");
}
}
Rather than having to construct an ErrorAsOutParameter under every conditional
where Err is known to be non-null.
llvm-svn: 276430
When concatenating two error lists the ErrorList::join method (which is called
by joinErrors) was failing to set the checked bit on the second error, leading
to a 'failure to check error' assertion.
llvm-svn: 274249
StringError can be used to represent Errors that aren't recoverable based on
the error type, but that have a useful error message that can be reported to
the user or logged.
llvm-svn: 270948
toString() consumes an Error and returns a string representation of its
contents. This commit also adds a message() method to ErrorInfoBase for
convenience.
Differential Revision: http://reviews.llvm.org/D19883
llvm-svn: 268465
destruction.
This makes the Expected<T> class behave like Error, even when in success mode.
Expected<T> values must be checked to see whether they contain an error prior
to being dereferenced, assigned to, or destructed.
llvm-svn: 265446
This helper method creates a pre-checked Error suitable for use as an out
parameter in a constructor. This avoids the need to have the constructor
check a known-good error before assigning to it.
llvm-svn: 264467
This is a temporary crutch to enable code that currently uses std::error_code
to be incrementally moved over to Error. Requiring all Error instances be
convertible enables clients to call errorToErrorCode on any error (not just
ECErrors created by conversion *from* an error_code).
This patch also moves code for Error from ErrorHandling.cpp into a new
Error.cpp file.
llvm-svn: 264221
idiom.
Most LLVM tool code exits immediately when an error is encountered and prints an
error message to stderr. The ExitOnError class supports this by providing two
call operators - one for Errors, and one for Expected<T>s. Calls to code that
can return Errors (or Expected<T>s) can use these calls to bail out on error,
and otherwise continue as if the operation had succeeded. E.g.
Error foo();
Expected<int> bar();
int main(int argc, char *argv[]) {
ExitOnError ExitOnErr;
ExitOnErr.setBanner(std::string("Error in ") + argv[0] + ":");
// Exit if foo returns an error. No need to manually check error return.
ExitOnErr(foo());
// Exit if bar returns an error, otherwise unwrap the contained int and
// continue.
int X = ExitOnErr(bar());
// ...
return 0;
}
llvm-svn: 263749
This patch introduces the Error classs for lightweight, structured,
recoverable error handling. It includes utilities for creating, manipulating
and handling errors. The scheme is similar to exceptions, in that errors are
described with user-defined types. Unlike exceptions however, errors are
represented as ordinary return types in the API (similar to the way
std::error_code is used).
For usage notes see the LLVM programmer's manual, and the Error.h header.
Usage examples can be found in unittests/Support/ErrorTest.cpp.
Many thanks to David Blaikie, Mehdi Amini, Kevin Enderby and others on the
llvm-dev and llvm-commits lists for lots of discussion and review.
llvm-svn: 263609
Lang Hames