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This patch makes it possible to use varargs for calling conventions,
which are either based on C (like efiapi) or C is based
on them (for example sysv64 and win64).
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This attempts to bring better error messages to invalid method calls, by applying some heuristics to identify common mistakes.
The algorithm is inspired by Levenshtein distance and longest common sub-sequence. In essence, we treat the types of the function, and the types of the arguments you provided as two "words" and compute the edits to get from one to the other.
We then modify that algorithm to detect 4 cases:
- A function input is missing
- An extra argument was provided
- The type of an argument is straight up invalid
- Two arguments have been swapped
- A subset of the arguments have been shuffled
(We detect the last two as separate cases so that we can detect two swaps, instead of 4 parameters permuted.)
It helps to understand this argument by paying special attention to terminology: "inputs" refers to the inputs being *expected* by the function, and "arguments" refers to what has been provided at the call site.
The basic sketch of the algorithm is as follows:
- Construct a boolean grid, with a row for each argument, and a column for each input. The cell [i, j] is true if the i'th argument could satisfy the j'th input.
- If we find an argument that could satisfy no inputs, provided for an input that can't be satisfied by any other argument, we consider this an "invalid type".
- Extra arguments are those that can't satisfy any input, provided for an input that *could* be satisfied by another argument.
- Missing inputs are inputs that can't be satisfied by any argument, where the provided argument could satisfy another input
- Swapped / Permuted arguments are identified with a cycle detection algorithm.
As each issue is found, we remove the relevant inputs / arguments and check for more issues. If we find no issues, we match up any "valid" arguments, and start again.
Note that there's a lot of extra complexity:
- We try to stay efficient on the happy path, only computing the diagonal until we find a problem, and then filling in the rest of the matrix.
- Closure arguments are wrapped in a tuple and need to be unwrapped
- We need to resolve closure types after the rest, to allow the most specific type constraints
- We need to handle imported C functions that might be variadic in their inputs.
I tried to document a lot of this in comments in the code and keep the naming clear.
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It makes very little sense to maintain denylists of ABIs when, as far as
non-generic ABIs are concerned, targets usually only support a small
subset of the available ABIs.
This has historically been a cause of bugs such as us allowing use of
the platform-specific ABIs on x86 targets – these in turn would cause
LLVM errors or assertions to fire.
Fixes #57182
Sponsored by: standard.ai
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Highlight parts of fn in type errors
When a type error arises between two fn items, fn pointers or tuples,
highlight only the differing parts of each.
Examples:
<img width="699" alt="" src="https://user-images.githubusercontent.com/1606434/69487597-ab561600-0e11-11ea-9b4e-d4fd9e91d5dc.png">
<img width="528" alt="" src="https://user-images.githubusercontent.com/1606434/69487207-9033d800-0e0a-11ea-93e3-8c4d002411a5.png">
<img width="468" alt="" src="https://user-images.githubusercontent.com/1606434/69487208-9033d800-0e0a-11ea-92e3-2b2cee120335.png">
<img width="775" alt="" src="https://user-images.githubusercontent.com/1606434/69487209-9033d800-0e0a-11ea-9e68-7f6ed5c8cb08.png">
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When a type error arises between two fn items, fn pointers or tuples,
highlight only the differing parts of each.
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Clone for it.
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Function signatures with the `variadic` member set are actually
C-variadic functions. Make this a little more explicit by renaming the
`variadic` boolean value, `c_variadic`.
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Add support for defining C compatible variadic functions in unsafe rust
with extern "C".
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