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wchargin opened this issue Jan 13, 2021 · 4 comments
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Adding struct/variant causes inference error in unrelated code #80964

wchargin opened this issue Jan 13, 2021 · 4 comments
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C-bug Category: This is a bug.

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@wchargin
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wchargin commented Jan 13, 2021 •
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I tried this code:

//! Stripped-down repro case for a strange bug, wherein adding a new struct or enum variant can
//! surface type inference errors in completely unrelated code, even in different modules.

mod pb {
    #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, PartialOrd, Ord, ::prost::Enumeration)]
    #[repr(i32)]
    pub enum DataClass {
        Unknown = 0,
        Scalar = 1,
        Tensor = 2,
        BlobSequence = 3,
    }
    #[derive(Clone, PartialEq, ::prost::Message)]
    pub struct SummaryMetadata {
        #[prost(enumeration = "DataClass", tag = "4")]
        pub data_class: i32,
    }
}

pub fn test() {
    let md = pb::SummaryMetadata::default();
    assert_eq!(md.data_class, pb::DataClass::BlobSequence.into());
}

// Uncomment this line to create an inference error at line 19:
//pub struct Foo(serde_json::Error);

I expected it to compile, and it does. But when I uncomment the final
line, a new inference error appears on the assert_eq! line:

error[E0282]: type annotations needed
  --> src/lib.rs:22:59
   |
22 |     assert_eq!(md.data_class, pb::DataClass::BlobSequence.into());
   |                               ----------------------------^^^^--
   |                               |                           |
   |                               |                           cannot infer type for type parameter `T` declared on the trait `Into`
   |                               this method call resolves to `T`

By itself, the inference error seems reasonable enough, and I can just
add type annotations. But the change has nothing to do with the error.

This is a stripped-down example. In my real code, I’m adding a variant
to an existing error enum, and I see two inference errors in entirely
unrelated modules:

$ git diff -U1
diff --git a/tensorboard/data/server/lib.rs b/tensorboard/data/server/lib.rs
index f1def3891..357693441 100644
--- a/tensorboard/data/server/lib.rs
+++ b/tensorboard/data/server/lib.rs
@@ -19,2 +19,4 @@ limitations under the License.
 
+pub struct Foo(serde_json::Error);
+
 pub mod cli;

$ cargo check --tests
error[E0282]: type annotations needed
   --> data_compat.rs:456:67
    |
456 |             assert_eq!(md.data_class, pb::DataClass::BlobSequence.into());
    |                                       ----------------------------^^^^--
    |                                       |                           |
    |                                       |                           cannot infer type for type parameter `T` declared on the trait `Into`
    |                                       this method call resolves to `T`

error[E0282]: type annotations needed
   --> server.rs:629:37
    |
629 |         assert_eq!(xent_data.value, Vec::new());
    |                                     ^^^^^^^^ cannot infer type for type parameter `T`

Cloneable example:
https://github.com/wchargin/rust-inference-action-at-a-distance

Meta

Can repro in 1.48.0, 1.49.0-beta, and 2021-01-06 nightly.

cargo/rustc versions 
$ cargo --version --verbose
cargo 1.48.0 (65cbdd2dc 2020-10-14)
release: 1.48.0
commit-hash: 65cbdd2dc0b7e877577474b98b7d071308d0bb6f
commit-date: 2020-10-14

$ cargo +beta --version --verbose
cargo 1.49.0-beta (8662ab427 2020-11-12)
release: 1.49.0
commit-hash: 8662ab427a8d6ad8047811cc4d78dbd20dd07699
commit-date: 2020-11-12

$ cargo +nightly --version --verbose
cargo 1.51.0-nightly (329895f5b 2021-01-06)
release: 1.51.0
commit-hash: 329895f5b52a358e5d9ecb26215708b5cb31d906
commit-date: 2021-01-06
Cargo.toml 
[package]
name = "inference-action-at-a-distance"
version = "0.1.0"
edition = "2018"

[dependencies]
prost = "0.6.1"
serde_json = "1.0.59"
Cargo.lock 
# This file is automatically @generated by Cargo.
# It is not intended for manual editing.
[[package]]
name = "anyhow"
version = "1.0.38"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "afddf7f520a80dbf76e6f50a35bca42a2331ef227a28b3b6dc5c2e2338d114b1"

[[package]]
name = "bytes"
version = "0.5.6"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "0e4cec68f03f32e44924783795810fa50a7035d8c8ebe78580ad7e6c703fba38"

[[package]]
name = "either"
version = "1.6.1"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "e78d4f1cc4ae33bbfc157ed5d5a5ef3bc29227303d595861deb238fcec4e9457"

[[package]]
name = "inference-action-at-a-distance"
version = "0.1.0"
dependencies = [
 "prost",
 "serde_json",
]

[[package]]
name = "itertools"
version = "0.8.2"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "f56a2d0bc861f9165be4eb3442afd3c236d8a98afd426f65d92324ae1091a484"
dependencies = [
 "either",
]

[[package]]
name = "itoa"
version = "0.4.7"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "dd25036021b0de88a0aff6b850051563c6516d0bf53f8638938edbb9de732736"

[[package]]
name = "proc-macro2"
version = "1.0.24"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "1e0704ee1a7e00d7bb417d0770ea303c1bccbabf0ef1667dae92b5967f5f8a71"
dependencies = [
 "unicode-xid",
]

[[package]]
name = "prost"
version = "0.6.1"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "ce49aefe0a6144a45de32927c77bd2859a5f7677b55f220ae5b744e87389c212"
dependencies = [
 "bytes",
 "prost-derive",
]

[[package]]
name = "prost-derive"
version = "0.6.1"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "537aa19b95acde10a12fec4301466386f757403de4cd4e5b4fa78fb5ecb18f72"
dependencies = [
 "anyhow",
 "itertools",
 "proc-macro2",
 "quote",
 "syn",
]

[[package]]
name = "quote"
version = "1.0.8"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "991431c3519a3f36861882da93630ce66b52918dcf1b8e2fd66b397fc96f28df"
dependencies = [
 "proc-macro2",
]

[[package]]
name = "ryu"
version = "1.0.5"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "71d301d4193d031abdd79ff7e3dd721168a9572ef3fe51a1517aba235bd8f86e"

[[package]]
name = "serde"
version = "1.0.119"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "9bdd36f49e35b61d49efd8aa7fc068fd295961fd2286d0b2ee9a4c7a14e99cc3"

[[package]]
name = "serde_json"
version = "1.0.61"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "4fceb2595057b6891a4ee808f70054bd2d12f0e97f1cbb78689b59f676df325a"
dependencies = [
 "itoa",
 "ryu",
 "serde",
]

[[package]]
name = "syn"
version = "1.0.58"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "cc60a3d73ea6594cd712d830cc1f0390fd71542d8c8cd24e70cc54cdfd5e05d5"
dependencies = [
 "proc-macro2",
 "quote",
 "unicode-xid",
]

[[package]]
name = "unicode-xid"
version = "0.2.1"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "f7fe0bb3479651439c9112f72b6c505038574c9fbb575ed1bf3b797fa39dd564"
@wchargin wchargin added the C-bug Category: This is a bug. label Jan 13, 2021
@wchargin
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Perhaps related: #44345? Mine doesn’t involve a dep upgrade, though.

@jonas-schievink
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Presumably this happens when serde_json is loaded, so use serde_json as _; instead of the struct should also cause this

@wchargin
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Indeed, it does.

@jonas-schievink
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In that case, closing as a duplicate of #44345

wchargin added a commit to tensorflow/tensorboard that referenced this issue Jan 13, 2021
@wchargin
rust: define blob key encoding
a0e0556 
Summary:
The data provider RPC protocol requires servers to emit “blob keys”,
opaque, URL-safe tokens that uniquely identify blobs. This patch defines
an in-memory `BlobKey` struct with encoding and decoding. The wire
format is URL-safe base64 (with no padding) over JSON.

The seemingly unrelated changes are needed because loading `serde_json`
adds trait implementations that make some type inference inadmissible:
<rust-lang/rust#80964>

Test Plan:
Unit tests included.

wchargin-branch: rust-blob-keys
wchargin-source: bd9d325a73fb7757b2916e52a72c4e23255c51ed
@wchargin wchargin mentioned this issue Jan 13, 2021
Merged
wchargin added a commit to tensorflow/tensorboard that referenced this issue Jan 13, 2021
@wchargin
rust: define blob key encoding (#4545)
012b901 
Summary:
The data provider RPC protocol requires servers to emit “blob keys”,
opaque, URL-safe tokens that uniquely identify blobs. This patch defines
an in-memory `BlobKey` struct with encoding and decoding. The wire
format is URL-safe base64 (with no padding) over JSON.

The seemingly unrelated changes are needed because loading `serde_json`
adds trait implementations that make some type inference inadmissible:
<rust-lang/rust#80964>

Test Plan:
Unit tests included.

wchargin-branch: rust-blob-keys
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