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Better pretty printing for const raw pointers #65859

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Better pretty printing for const raw pointers #65859

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22586d7
Better pretty printing for const raw pointers
iwikal Oct 27, 2019
6a6ed12
Add the two missing hex digits
iwikal Oct 27, 2019
d322044
Fix raw const ptr test on 32 bit platforms
iwikal Oct 31, 2019
3364c46
Nicer fallback for const pointers to allocations
iwikal Nov 4, 2019
f2cb4d7
Print const refs like const raw pointers
iwikal Nov 4, 2019
6c26bd6
Try to print as slice before ref
iwikal Nov 11, 2019
175c608
Update expected output in mir-opt tests
iwikal Nov 11, 2019
c2dbe44
Bless mir-opt test
iwikal Nov 16, 2019
27d89ec
Merge branch 'master' into pretty-const-pointers
iwikal Nov 16, 2019
1407cdd
Comment which kinds of refs get printed where
iwikal Nov 16, 2019
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10 changes: 9 additions & 1 deletion src/librustc/ty/print/pretty.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -919,7 +919,15 @@ pub trait PrettyPrinter<'tcx>:
},
(ConstValue::Scalar(Scalar::Raw { data, .. }), ty::Char) =>
p!(write("{:?}", ::std::char::from_u32(data as u32).unwrap())),
(ConstValue::Scalar(_), ty::RawPtr(_)) => p!(write("{{pointer}}")),
(ConstValue::Scalar(value), ty::RawPtr(_)) => {
match value {
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So this is a "fallback" case now, right? We already have a big case for references above. Unfortunately it is not immediately clear what distinguishes these cases.

Could you add some comments both at the if let ty::Ref above and at the match arm here describing why we do the matches we do in the order they are, and which various cases of references each conditional covers?

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I don't know the history of that big if let ty::Ref statement or why it looks the way it does internally, so I don't feel comfortable documenting it. But I added a comment specifying that it needs to happen before the general case.

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From what I can see, the point of that is to print the content of the slice/array when possible for types &[u8], [u8; N] and &str. Do you agree? If yes, please write that. Right now you only mention &str but that is not the only type handled here.

The fallback then is that for all other references and raw pointers, we just print the pointer value, not the thing it points to.

Scalar::Raw { data, size } => {
p!(write("0x{:01$x} : ", data, size as usize * 2));
}
_ => p!(write("{{pointer}} : "))
};
p!(print(ct.ty));
}
(ConstValue::Scalar(Scalar::Ptr(ptr)), ty::FnPtr(_)) => {
let instance = {
let alloc_map = self.tcx().alloc_map.lock();
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5 changes: 5 additions & 0 deletions src/test/ui/const-generics/raw-ptr-const-param.rs
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@@ -1,3 +1,6 @@
// normalize-stderr-32bit: "0x" -> "$$PREFIX"
// normalize-stderr-64bit: "0x00000000" -> "$$PREFIX"

#![feature(const_generics, const_compare_raw_pointers)]
//~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash

Expand All @@ -6,4 +9,6 @@ struct Const<const P: *const u32>;
fn main() {
let _: Const<{15 as *const _}> = Const::<{10 as *const _}>; //~ mismatched types
let _: Const<{10 as *const _}> = Const::<{10 as *const _}>;

let _: Const<{10 as *const _}> = Const::<{&8_u32 as *const _}>; //~ mismatched types
}
21 changes: 15 additions & 6 deletions src/test/ui/const-generics/raw-ptr-const-param.stderr
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@@ -1,20 +1,29 @@
warning: the feature `const_generics` is incomplete and may cause the compiler to crash
--> $DIR/raw-ptr-const-param.rs:1:12
--> $DIR/raw-ptr-const-param.rs:4:12
|
LL | #![feature(const_generics, const_compare_raw_pointers)]
| ^^^^^^^^^^^^^^
|
= note: `#[warn(incomplete_features)]` on by default

error[E0308]: mismatched types
--> $DIR/raw-ptr-const-param.rs:7:38
--> $DIR/raw-ptr-const-param.rs:10:38
|
LL | let _: Const<{15 as *const _}> = Const::<{10 as *const _}>;
| ^^^^^^^^^^^^^^^^^^^^^^^^^ expected `{pointer}`, found `{pointer}`
| ^^^^^^^^^^^^^^^^^^^^^^^^^ expected `$PREFIX0000000f : *const u32`, found `$PREFIX0000000a : *const u32`
|
= note: expected type `Const<{pointer}>`
found type `Const<{pointer}>`
= note: expected type `Const<$PREFIX0000000f : *const u32>`
found type `Const<$PREFIX0000000a : *const u32>`

error: aborting due to previous error
error[E0308]: mismatched types
--> $DIR/raw-ptr-const-param.rs:13:38
|
LL | let _: Const<{10 as *const _}> = Const::<{&8_u32 as *const _}>;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `$PREFIX0000000a : *const u32`, found `{pointer} : *const u32`
|
= note: expected type `Const<$PREFIX0000000a : *const u32>`
found type `Const<{pointer} : *const u32>`

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0308`.