Refactor fallibility of conversions from IR to Rust types #581
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fitzgen
commented
Mar 14, 2017
src/codegen/mod.rs
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| primitive_ty(ctx, "isize") | ||
| } | ||
| _ => return None, | ||
| }) |
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Note to self: remove this leftover from rebasing away a bad cargo fmt.
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Also, I should add the original test case from #573 (comment) to our test suite. |
emilio
approved these changes
Mar 15, 2017
src/codegen/error.rs
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| /// Errors that can occur during code generation. | ||
| #[derive(Clone, Debug, PartialEq, Eq)] | ||
| pub enum Error { | ||
| NoLayoutForOpaqueBlob, |
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Document the variants, please :)
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| /// Errors that can occur during code generation. | ||
| #[derive(Clone, Debug, PartialEq, Eq)] | ||
| pub enum Error { |
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This seems like an overly generic name for a really specific error kind. I don't have a clearly better name in mind though.
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It is namespaced, however. I hope that it can become the error type for all fallible codegen operations.
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The old ToRustTy and ItemToRustTy conversion traits were problematic
in that they assumed infallibity. That assumption is problematic
because we are often dealing with C++ constructs for which Rust has no
equivalent *and* we don't have a usable layout from which to generate
an opaque blob in its stead. But, a usable layout is often "up the
stack" if only we had a way to get up there.
For example, Rust does not currently have an equivalent of const value
template parameters, and libclang will not give us a layout for
template definitions with const value template parameters. However,
libclang will give us the layout for an instantiation of such a
template definition.
First, this commit separates the concepts of generating an equivalent
Rust type from generating an opaque blob of the same size and
alignment as an IR thing. This consolidates and DRYs up a *ton* of
code involved in falling back to an opaque blob (and doing our best to
get a Layout for the blob) when we can't generate an equivalent Rust
type for some IR thing.
Second, it separates fallible and infallible conversions, and provides
a nice little framework for when to choose which. This gives us one
single place where we do this whole dance:
if could not generate equivalent Rust type:
if we have a layout:
return opaque blob based on layout
else:
return opaque blob based on a wish and a prayer
The ToRustTy trait is replaced by the TryToOpaque, ToOpaque,
TryToRustTyOrOpaque, and ToRustTyOrOpaque traits. The ItemToRustTy
helper was just a way to avoid ToRustTy's Self::Extra parameter when
it was not needed, and is simply removed without a replacement. We
suck it up and pass `&()` at call sites now. We *could* introduce
ItemTryToOpaque, ItemToOpaque, etc... traits, but the cost of the
added boiler plate would outweigh the benefits of not passing `&()` at
call sites, IMHO.
In addition to being a nice code cleanup, this also fixes rust-lang#573.
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…test-failures, r=emilio
Refactor fallibility of conversions from IR to Rust types
The old `ToRustTy` and `ItemToRustTy` conversion traits were problematic in that they assumed infallibity. That assumption is problematic because we are often dealing with C++ constructs for which Rust has no equivalent *and* we don't have a usable layout from which to generate an opaque blob in its stead. But, a usable layout is often "up the stack" if only we had a way to get up there.
For example, Rust does not currently have an equivalent of const value template parameters, and libclang will not give us a layout for template definitions with const value template parameters. However, libclang will give us the layout for an instantiation of such a template definition.
First, this commit separates the concepts of generating an equivalent Rust type from generating an opaque blob of the same size and alignment as an IR thing. This consolidates and DRYs up a *ton* of code involved in falling back to an opaque blob (and doing our best to get a `Layout` for the blob) when we can't generate an equivalent Rust type for some IR thing.
Second, it separates fallible and infallible conversions, and provides a nice little framework for when to choose which. This gives us one single place where we do this whole dance:
if could not generate equivalent Rust type:
if we have a layout:
return opaque blob based on layout
else:
return opaque blob based on a wish and a prayer
The `ToRustTy` trait is replaced by the `TryToOpaque`, `ToOpaque`, `TryToRustTyOrOpaque`, and `ToRustTyOrOpaque` traits. The `ItemToRustTy` helper was just a way to avoid `ToRustTy`'s `Self::Extra` parameter when it was not needed, and is simply removed without a replacement. We suck it up and pass `&()` at call sites now. We *could* introduce `ItemTryToOpaque`, `ItemToOpaque`, etc... traits, but the cost of the added boiler plate would outweigh the benefits of not passing `&()` at call sites, IMHO.
In addition to being a nice code cleanup, this also fixes #573.
r? @emilio
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The old
ToRustTyandItemToRustTyconversion traits were problematic in that they assumed infallibity. That assumption is problematic because we are often dealing with C++ constructs for which Rust has no equivalent and we don't have a usable layout from which to generate an opaque blob in its stead. But, a usable layout is often "up the stack" if only we had a way to get up there.For example, Rust does not currently have an equivalent of const value template parameters, and libclang will not give us a layout for template definitions with const value template parameters. However, libclang will give us the layout for an instantiation of such a template definition.
First, this commit separates the concepts of generating an equivalent Rust type from generating an opaque blob of the same size and alignment as an IR thing. This consolidates and DRYs up a ton of code involved in falling back to an opaque blob (and doing our best to get a
Layoutfor the blob) when we can't generate an equivalent Rust type for some IR thing.Second, it separates fallible and infallible conversions, and provides a nice little framework for when to choose which. This gives us one single place where we do this whole dance:
The
ToRustTytrait is replaced by theTryToOpaque,ToOpaque,TryToRustTyOrOpaque, andToRustTyOrOpaquetraits. TheItemToRustTyhelper was just a way to avoidToRustTy'sSelf::Extraparameter when it was not needed, and is simply removed without a replacement. We suck it up and pass&()at call sites now. We could introduceItemTryToOpaque,ItemToOpaque, etc... traits, but the cost of the added boiler plate would outweigh the benefits of not passing&()at call sites, IMHO.In addition to being a nice code cleanup, this also fixes #573.
r? @emilio