Improve debugging experience for enums on windows-msvc #85292

wesleywiser · 2021-05-14T14:50:51Z

This PR makes significant improvements over the status quo of debugging enums on the windows-msvc platform with either WinDbg or Visual Studio in three ways:

Improves the debugger experience for directly tagged enums.
Fixes a bug which caused the debugger to sometimes show the wrong debug info for niche layout enums. For example, Option<&u32> could sometimes use the debug info for Option<&f64> instead leading to nonsensical variable values in the debugger.
Significantly improves the debugger experience for niche-layout enums.

Let's look at a few examples:

pub enum CStyleEnum {
    Base = 2,
    Exponent = 16,
}

pub enum NicheLayoutEnum {
    Tag1,
    Data { my_data: CStyleEnum },
    Tag2,
    Tag3,
    Tag4,
}

pub enum OtherEnum<T> {
    Case1(T),
    Case2(T),
}

fn main() {
    let a = Some(CStyleEnum::Base);
    let b = Option::<CStyleEnum>::None;
    let c = NicheLayoutEnum::Tag1;
    let d = NicheLayoutEnum::Data { my_data: CStyleEnum::Exponent };
    let e = NicheLayoutEnum::Tag2;
    let f = Some(&1u32);
    let g = Option::<&'static u32>::None;
    let h = Some(&2u64);
    let i = Option::<&'static u64>::None;
    let j = Some(12u32);
    let k = Option::<u32>::None;
    let l = Some(12.34f64);
    let m = Option::<f64>::None;
    let n = CStyleEnum::Base;
    let o = CStyleEnum::Exponent;
    let p = Some("IAMA optional string!".to_string());
    let q = OtherEnum::Case1(42u32);
}

This is what WinDbg Preview shows using the latest rustc nightly:

Most of the variables don't show a meaningful value expect for a few cases that we have targeted natvis definitions covering. Even worse, drilling into many of these variables shows information that can be difficult to interpret without an understanding of the layout of Rust types:

With the changes in this PR, we're able to write two natvis definitions that cover all enum cases generally. After building with these changes, WinDbg now shows this instead:

Drilling into the same variables, we can see much more useful information:

Fixes #84670
Fixes #84671

rust-highfive · 2021-05-14T14:50:54Z

r? @davidtwco

(rust-highfive has picked a reviewer for you, use r? to override)

wesleywiser · 2021-05-14T14:57:01Z

As a question for reviewers, if you look at the screenshots, you'll notice that sometimes Option::Some is visualized as Some({...}) and sometimes it's just Some. This is because the niche-layout visualization knows the Some variant has data but the general enum visualization does not know which variants have data and which do not. I chose to do it this way because it does improve the experience of niche-layout enums in general but it also causes this inconsistency.

I think it is possible to further improve the general enum visualization further in follow up PRs. Please let me know if you have an opinion on the current state.

vadimcn

Thanks for tackling this!

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

compiler/rustc_codegen_ssa/src/debuginfo/type_names.rs

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

wesleywiser · 2021-05-21T16:22:14Z

Assigning to @michaelwoerister since he's looking at #85269 as well.

r? @michaelwoerister

michaelwoerister

Thanks for the PR, @wesleywiser! This looks like it should really improve the debugging experience for enums. It's great that you found an encoding that NatVis can handle robustly. I'm sure it was a lot of work to get there!

I've left some comments below. I'd also like to suggest to make the compiler generated names more consistent:

type names should start with an uppercase letter (e.g. Tag$ instead of tag$),
field names should start with a lowercase letter (e.g. variant0 instead of Variant0),
either all generated names should end with $ or only those that could potentially conflict with a non-generated name.
use only one of the terms tag$, discriminant$, and variant$. Right now all three of them seem to be in use but refer to the same thing.

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

src/etc/natvis/intrinsic.natvis

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

compiler/rustc_codegen_ssa/src/debuginfo/type_names.rs

wesleywiser · 2021-05-28T21:31:00Z

Thanks for the review @michaelwoerister! I think I've addressed all your feedback in the latest commit.

michaelwoerister

Thanks, @wesleywiser! I think this is almost ready to merge. I left a few comments below. I'm being nitpicky about typo because, for someone who does not know the code, it can be very hard to tell if something is just an oversight or if it has some kind of special meaning.

Otherwise, consider the PR approved by me 😀

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

michaelwoerister · 2021-05-31T09:47:01Z

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

+                    // ```c
+                    // union enum$<{name}> {
+                    //   struct {variant 0 name} {
+                    //     tag$ variant$;


I still think it would be more consistent if the variant$ field here and the discriminant field in the niche-layout union would use the same name (e.g. discriminant$ or tag$) 😃

Eventually, I would like to have all enums use the [variant] synthetic item to name the variant they are currently in and hide all of the discriminant fields. This is how it currently works for niche-layout enums but not for directly tagged ones. This will require some more work on the directly tagged case and I'd like to go ahead and get this merged since I don't think it's worth holding this improvement up for that as variant$ is still better than RUST$ENUM$DISR which we have today.

I would also rather not change the niche-layout ones as discriminant is the correct terminology to use in that case. Feel free to r- if you think we should still do something different here!

@wesleywiser So are you planning more changes for enums?

Yes, I'm hoping to have time this week to get to it.

IMO, it'd be nice to move discriminant out of the variant structs. Otherwise it can be seen when displaying fields of the variant struct, and hiding it is kinda annoying.

Also, I notice that tuple struct variants are not tagged as such, which means that tuple visualizers won't be applied to them.
(i.e. enum$<EnumName>::VariantX should be tuple<enum$<EnumName>::VariantX>?)

wesleywiser · 2021-06-01T15:49:34Z

@bors r=michaelwoerister

bors · 2021-06-01T15:49:36Z

📌 Commit 6d0afc473bca02cbbc528b12116a0cb5320a832b has been approved by michaelwoerister

bors · 2021-06-01T22:32:13Z

⌛ Testing commit 6d0afc473bca02cbbc528b12116a0cb5320a832b with merge 4b3463e626e30ed451eeadabed0e44099cf9402e...

bors · 2021-06-01T23:02:46Z

💔 Test failed - checks-actions

This makes the type name inline with the proposed standard in rust-lang#85269.

wesleywiser · 2021-06-02T20:28:31Z

@bors r=michaelwoerister

bors · 2021-06-02T20:28:33Z

📌 Commit 94c45ef has been approved by michaelwoerister

…elwoerister Improve debugging experience for enums on windows-msvc This PR makes significant improvements over the status quo of debugging enums on the windows-msvc platform with either WinDbg or Visual Studio in three ways: 1. Improves the debugger experience for directly tagged enums. 2. Fixes a bug which caused the debugger to sometimes show the wrong debug info for niche layout enums. For example, `Option<&u32>` could sometimes use the debug info for `Option<&f64>` instead leading to nonsensical variable values in the debugger. 3. Significantly improves the debugger experience for niche-layout enums. Let's look at a few examples: ```rust pub enum CStyleEnum { Base = 2, Exponent = 16, } pub enum NicheLayoutEnum { Tag1, Data { my_data: CStyleEnum }, Tag2, Tag3, Tag4, } pub enum OtherEnum<T> { Case1(T), Case2(T), } fn main() { let a = Some(CStyleEnum::Base); let b = Option::<CStyleEnum>::None; let c = NicheLayoutEnum::Tag1; let d = NicheLayoutEnum::Data { my_data: CStyleEnum::Exponent }; let e = NicheLayoutEnum::Tag2; let f = Some(&1u32); let g = Option::<&'static u32>::None; let h = Some(&2u64); let i = Option::<&'static u64>::None; let j = Some(12u32); let k = Option::<u32>::None; let l = Some(12.34f64); let m = Option::<f64>::None; let n = CStyleEnum::Base; let o = CStyleEnum::Exponent; let p = Some("IAMA optional string!".to_string()); let q = OtherEnum::Case1(42u32); } ``` This is what WinDbg Preview shows using the latest rustc nightly: ![image](https://user-images.githubusercontent.com/831192/118285353-57c10780-b49f-11eb-97aa-db3abfc09508.png) Most of the variables don't show a meaningful value expect for a few cases that we have targeted natvis definitions covering. Even worse, drilling into many of these variables shows information that can be difficult to interpret without an understanding of the layout of Rust types: ![image](https://user-images.githubusercontent.com/831192/118285609-a1a9ed80-b49f-11eb-9c29-b14576984647.png) With the changes in this PR, we're able to write two natvis definitions that cover all enum cases generally. After building with these changes, WinDbg now shows this instead: ![image](https://user-images.githubusercontent.com/831192/118287730-be472500-b4a1-11eb-8cad-8f6a91c7516b.png) Drilling into the same variables, we can see much more useful information: ![image](https://user-images.githubusercontent.com/831192/118287888-e20a6b00-b4a1-11eb-927f-32cf33a31c16.png) Fixes rust-lang#84670 Fixes rust-lang#84671

bors · 2021-06-03T13:10:17Z

⌛ Testing commit 94c45ef with merge 431ea5ab6bee9d04b74e56a0c24c65a3e524b7ea...

bors · 2021-06-03T15:06:23Z

💔 Test failed - checks-actions

rust-log-analyzer · 2021-06-03T15:06:26Z

A job failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

wesleywiser · 2021-06-03T15:14:11Z

@bors retry

bors · 2021-06-03T15:32:43Z

⌛ Testing commit 94c45ef with merge 2577825...

bors · 2021-06-03T18:13:22Z

☀️ Test successful - checks-actions
Approved by: michaelwoerister
Pushing 2577825 to master...

This isn't used anymore after rust-lang#85292

Pkgsrc changes: * Bump bootstrap requirements to 1.53.0. * Adjust patches, adapt to upstream changes, adjust cargo checksums * If using an external llvm, require >= 10.0 Upsteream changes: Version 1.54.0 (2021-07-29) ============================ Language ----------------------- - [You can now use macros for values in built-in attribute macros.][83366] While a seemingly minor addition on its own, this enables a lot of powerful functionality when combined correctly. Most notably you can now include external documentation in your crate by writing the following. ```rust #![doc = include_str!("README.md")] ``` You can also use this to include auto-generated modules: ```rust #[path = concat!(env!("OUT_DIR"), "/generated.rs")] mod generated; ``` - [You can now cast between unsized slice types (and types which contain unsized slices) in `const fn`.][85078] - [You can now use multiple generic lifetimes with `impl Trait` where the lifetimes don't explicitly outlive another.][84701] In code this means that you can now have `impl Trait<'a, 'b>` where as before you could only have `impl Trait<'a, 'b> where 'b: 'a`. Compiler ----------------------- - [Rustc will now search for custom JSON targets in `/lib/rustlib/<target-triple>/target.json` where `/` is the "sysroot" directory.][83800] You can find your sysroot directory by running `rustc --print sysroot`. - [Added `wasm` as a `target_family` for WebAssembly platforms.][84072] - [You can now use `#[target_feature]` on safe functions when targeting WebAssembly platforms.][84988] - [Improved debugger output for enums on Windows MSVC platforms.][85292] - [Added tier 3\* support for `bpfel-unknown-none` and `bpfeb-unknown-none`.][79608] \* Refer to Rust's [platform support page][platform-support-doc] for more information on Rust's tiered platform support. Libraries ----------------------- - [`panic::panic_any` will now `#[track_caller]`.][85745] - [Added `OutOfMemory` as a variant of `io::ErrorKind`.][84744] - [ `proc_macro::Literal` now implements `FromStr`.][84717] - [The implementations of vendor intrinsics in core::arch have been significantly refactored.][83278] The main user-visible changes are a 50% reduction in the size of libcore.rlib and stricter validation of constant operands passed to intrinsics. The latter is technically a breaking change, but allows Rust to more closely match the C vendor intrinsics API. Stabilized APIs --------------- - [`BTreeMap::into_keys`] - [`BTreeMap::into_values`] - [`HashMap::into_keys`] - [`HashMap::into_values`] - [`arch::wasm32`] - [`VecDeque::binary_search`] - [`VecDeque::binary_search_by`] - [`VecDeque::binary_search_by_key`] - [`VecDeque::partition_point`] Cargo ----- - [Added the `--prune <spec>` option to `cargo-tree` to remove a package from the dependency graph.][cargo/9520] - [Added the `--depth` option to `cargo-tree` to print only to a certain depth in the tree ][cargo/9499] - [Added the `no-proc-macro` value to `cargo-tree --edges` to hide procedural macro dependencies.][cargo/9488] - [A new environment variable named `CARGO_TARGET_TMPDIR` is available.][cargo/9375] This variable points to a directory that integration tests and benches can use as a "scratchpad" for testing filesystem operations. Compatibility Notes ------------------- - [Mixing Option and Result via `?` is no longer permitted in closures for inferred types.][86831] - [Previously unsound code is no longer permitted where different constructors in branches could require different lifetimes.][85574] - As previously mentioned the [`std::arch` instrinsics now uses stricter const checking][83278] than before and may reject some previously accepted code. - [`i128` multiplication on Cortex M0+ platforms currently unconditionally causes overflow when compiled with `codegen-units = 1`.][86063] [85574]: rust-lang/rust#85574 [86831]: rust-lang/rust#86831 [86063]: rust-lang/rust#86063 [86831]: rust-lang/rust#86831 [79608]: rust-lang/rust#79608 [84988]: rust-lang/rust#84988 [84701]: rust-lang/rust#84701 [84072]: rust-lang/rust#84072 [85745]: rust-lang/rust#85745 [84744]: rust-lang/rust#84744 [85078]: rust-lang/rust#85078 [84717]: rust-lang/rust#84717 [83800]: rust-lang/rust#83800 [83366]: rust-lang/rust#83366 [83278]: rust-lang/rust#83278 [85292]: rust-lang/rust#85292 [cargo/9520]: rust-lang/cargo#9520 [cargo/9499]: rust-lang/cargo#9499 [cargo/9488]: rust-lang/cargo#9488 [cargo/9375]: rust-lang/cargo#9375 [`BTreeMap::into_keys`]: https://doc.rust-lang.org/std/collections/struct.BTreeMap.html#method.into_keys [`BTreeMap::into_values`]: https://doc.rust-lang.org/std/collections/struct.BTreeMap.html#method.into_values [`HashMap::into_keys`]: https://doc.rust-lang.org/std/collections/struct.HashMap.html#method.into_keys [`HashMap::into_values`]: https://doc.rust-lang.org/std/collections/struct.HashMap.html#method.into_values [`arch::wasm32`]: https://doc.rust-lang.org/core/arch/wasm32/index.html [`VecDeque::binary_search`]: https://doc.rust-lang.org/std/collections/struct.VecDeque.html#method.binary_search [`VecDeque::binary_search_by`]: https://doc.rust-lang.org/std/collections/struct.VecDeque.html#method.binary_search_by [`VecDeque::binary_search_by_key`]: https://doc.rust-lang.org/std/collections/struct.VecDeque.html#method.binary_search_by_key [`VecDeque::partition_point`]: https://doc.rust-lang.org/std/collections/struct.VecDeque.html#method.partition_point

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wesleywiser added A-debuginfo Area: Debugging information in compiled programs (DWARF, PDB, etc.) O-windows-msvc Toolchain: MSVC, Operating system: Windows labels May 14, 2021

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wesleywiser added 4 commits June 2, 2021 10:23

Respond to review feedback

d2d6fa8

Change the type name from _enum<..> to enum$<..>

ef053fd

This makes the type name inline with the proposed standard in rust-lang#85269.

Respond to review feedback

3127419

Update generator tests

94c45ef

wesleywiser force-pushed the enum_debuginfo branch from 6d0afc4 to 94c45ef Compare June 2, 2021 20:09

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jun 2, 2021

Dylan-DPC-zz mentioned this pull request Jun 3, 2021

Rollup of 13 pull requests #85949

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bors merged commit 2577825 into rust-lang:master Jun 3, 2021

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Improve debug symbol names to avoid ambiguity and work better with MSVC's debugger #85269

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wesleywiser added a commit to wesleywiser/rust that referenced this pull request Jul 3, 2021

Remove unnecessary visualizer

9b5fe6e

This isn't used anymore after rust-lang#85292

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