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[3/n] [daft-derive] attempt to better annotate semantic errors
Add some span info to try and annotate semantic errors better (such as highlighting the name of the field that's not diffable). This isn't perfect for now because we still produce some call-site errors, but at least we produce one error that's attributed directly to the field name so rust-analyzer should be happy. I tried adding more bounds but ran into rust-lang/rust#48214. Reviewers: andrewjstone Reviewed By: andrewjstone Pull Request: #60
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8 files changed

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‎.github/workflows/ci.yml

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@@ -38,11 +38,38 @@ jobs:
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build-and-test:
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name: Build and test
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runs-on: ${{ matrix.os }}
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strategy:
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matrix:
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os: [ubuntu-latest]
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fail-fast: false
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env:
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RUSTFLAGS: -D warnings
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CARGO_TERM_COLOR: always
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steps:
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- uses: actions/checkout@eef61447b9ff4aafe5dcd4e0bbf5d482be7e7871 # v4
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- name: Install toolchain in rust-toolchain.toml
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# GitHub Actions has an older rustup as of 2025-03-07 which doesn't accept
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# `rustup toolchain install` with no arguments. Update rustup first.
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run: rustup self update && rustup toolchain install
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- uses: Swatinem/rust-cache@23bce251a8cd2ffc3c1075eaa2367cf899916d84 # v2
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- uses: taiki-e/install-action@cargo-hack
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- uses: taiki-e/install-action@just
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- uses: taiki-e/install-action@nextest
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- name: Build
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run: just powerset build
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- name: Run tests
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run: just powerset nextest run
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- name: Doctests
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run: just powerset test --doc
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build-and-test-msrv:
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name: Build and test (MSRV)
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runs-on: ${{ matrix.os }}
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strategy:
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matrix:
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os: [ubuntu-latest]
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# 1.81 is the MSRV
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rust-version: ["1.81", stable]
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rust-version: ["1.81"]
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fail-fast: false
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env:
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RUSTFLAGS: -D warnings
@@ -54,7 +81,11 @@ jobs:
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- uses: Swatinem/rust-cache@23bce251a8cd2ffc3c1075eaa2367cf899916d84 # v2
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- uses: taiki-e/install-action@cargo-hack
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- uses: taiki-e/install-action@just
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- uses: taiki-e/install-action@nextest
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- name: Build
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run: just powerset build
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- name: Test
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run: just powerset test
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# We don't run ui_test on the MSRV since compiler output varies by version.
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- name: Test without ui_test
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run: just powerset nextest run -E 'not binary(ui_test)'
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- name: Doctests
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run: just powerset test --doc

‎Justfile

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@@ -1,3 +1,5 @@
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set positional-arguments
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# Note: help messages should be 1 line long as required by just.
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# Print a help message.
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powerset *args:
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# Group third-party implementation features to avoid a full combinatorial
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# explosion -- we assume that they build independent of each other.
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cargo hack --feature-powerset --workspace {{args}} --group-features newtype-uuid1,oxnet01,uuid1 --ignore-unknown-features
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cargo hack --feature-powerset --workspace "$@" --group-features newtype-uuid1,oxnet01,uuid1 --ignore-unknown-features
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# Build docs for crates and direct dependencies
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rustdoc *args:

‎daft-derive/src/internals/imp.rs

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@@ -1,10 +1,11 @@
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use super::error_store::{ErrorSink, ErrorStore};
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use proc_macro2::{Span, TokenStream};
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use quote::{quote, ToTokens};
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use quote::{quote, quote_spanned, ToTokens};
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use syn::{
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parse_quote, parse_str, visit::Visit, Attribute, Data, DataStruct,
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DeriveInput, Expr, Field, Fields, GenericParam, Generics, Index, Lifetime,
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LifetimeParam, Path, Token, WhereClause, WherePredicate,
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parse_quote, parse_quote_spanned, parse_str, spanned::Spanned,
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visit::Visit, Attribute, Data, DataStruct, DeriveInput, Expr, Field,
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Fields, GenericParam, Generics, Index, Lifetime, LifetimeParam, Path,
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Token, WhereClause, WherePredicate,
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};
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pub struct DeriveDiffableOutput {
@@ -563,11 +564,11 @@ impl DiffFields {
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let mut f = f.clone();
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f.ty = if config.mode == FieldMode::Leaf {
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parse_quote! {
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parse_quote_spanned! {f.span()=>
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#daft_crate::Leaf<&#lt #ty>
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}
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} else {
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parse_quote! {
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parse_quote_spanned! {f.span()=>
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<#ty as #daft_crate::Diffable>::Diff<#lt>
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}
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};
@@ -591,7 +592,7 @@ impl DiffFields {
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trait_bound: &syn::TraitBound,
592593
) -> WhereClause {
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let predicates = self.types().map(|ty| -> WherePredicate {
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parse_quote! {
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parse_quote_spanned! {ty.span()=>
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#ty: #trait_bound
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}
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});
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}
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};
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if config.mode == FieldMode::Leaf {
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quote! {
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quote_spanned! {f.span()=>
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#field_name: #daft_crate::Leaf {
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before: &self.#field_name,
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after: &other.#field_name
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}
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}
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} else {
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quote! {
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quote_spanned! {f.span()=>
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#field_name: #daft_crate::Diffable::diff(
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&self.#field_name,
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&other.#field_name

‎daft-derive/tests/fixtures/README.md

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@@ -20,4 +20,4 @@ These fixtures ensure that:
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Each file in `invalid` is automatically picked up by the snapshot and UI tests.
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Like with valid fixtures, `snapshot_test.rs` tests all macro invocations annotated with `#[derive(Diffable)]`.
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Like with valid fixtures, `snapshot_test.rs` tests all macro invocations annotated with `#[derive(Diffable)]`.

‎daft-derive/tests/fixtures/invalid/output/struct-field-not-diffable.output.rs

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struct MyStructDiff<'__daft> {
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a: <i32 as ::daft::Diffable>::Diff<'__daft>,
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b: <NonDiffable as ::daft::Diffable>::Diff<'__daft>,
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}
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impl<'__daft> ::std::fmt::Debug for MyStructDiff<'__daft>
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where
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<i32 as ::daft::Diffable>::Diff<'__daft>: ::std::fmt::Debug,
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<NonDiffable as ::daft::Diffable>::Diff<'__daft>: ::std::fmt::Debug,
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{
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fn fmt(&self, f: &mut ::std::fmt::Formatter<'_>) -> ::std::fmt::Result {
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f.debug_struct(stringify!(MyStructDiff))
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.field(stringify!(a), &self.a)
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.field(stringify!(b), &self.b)
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.finish()
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}
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}
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impl<'__daft> ::std::cmp::PartialEq for MyStructDiff<'__daft>
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where
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<i32 as ::daft::Diffable>::Diff<'__daft>: ::std::cmp::PartialEq,
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<NonDiffable as ::daft::Diffable>::Diff<'__daft>: ::std::cmp::PartialEq,
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{
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fn eq(&self, other: &Self) -> bool {
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self.a == other.a && self.b == other.b
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}
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}
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impl<'__daft> ::std::cmp::Eq for MyStructDiff<'__daft>
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where
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<i32 as ::daft::Diffable>::Diff<'__daft>: ::std::cmp::Eq,
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<NonDiffable as ::daft::Diffable>::Diff<'__daft>: ::std::cmp::Eq,
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{}
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impl ::daft::Diffable for MyStruct {
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type Diff<'__daft> = MyStructDiff<'__daft> where Self: '__daft;
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fn diff<'__daft>(&'__daft self, other: &'__daft Self) -> MyStructDiff<'__daft> {
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Self::Diff {
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a: ::daft::Diffable::diff(&self.a, &other.a),
36+
b: ::daft::Diffable::diff(&self.b, &other.b),
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}
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}
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}

‎daft-derive/tests/fixtures/invalid/struct-field-not-diffable.rs

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use daft::Diffable;
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struct NonDiffable {}
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#[derive(Diffable)]
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struct MyStruct {
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a: i32,
8+
b: NonDiffable,
9+
}
10+
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fn main() {
12+
// MyStruct should still exist, even though the Diffable impl has errors.
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let _ = MyStruct { a: 0, b: NonDiffable {} };
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}

‎daft-derive/tests/fixtures/invalid/struct-field-not-diffable.stderr

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error[E0277]: the trait bound `NonDiffable: Diffable` is not satisfied
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--> tests/fixtures/invalid/struct-field-not-diffable.rs:8:5
3+
|
4+
8 | b: NonDiffable,
5+
| ^ the trait `Diffable` is not implemented for `NonDiffable`
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|
7+
= help: the following other types implement trait `Diffable`:
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&'a T
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()
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(A, B)
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(A, B, C)
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(A, B, C, D)
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(A, B, C, D, E)
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(A, B, C, D, E, F)
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(A, B, C, D, E, F, G)
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and $N others
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18+
error[E0277]: the trait bound `NonDiffable: Diffable` is not satisfied
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--> tests/fixtures/invalid/struct-field-not-diffable.rs:5:10
20+
|
21+
5 | #[derive(Diffable)]
22+
| ^^^^^^^^ the trait `Diffable` is not implemented for `NonDiffable`
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|
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= help: the following other types implement trait `Diffable`:
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&'a T
26+
()
27+
(A, B)
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(A, B, C)
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(A, B, C, D)
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(A, B, C, D, E)
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(A, B, C, D, E, F)
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(A, B, C, D, E, F, G)
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and $N others
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= note: this error originates in the derive macro `Diffable` (in Nightly builds, run with -Z macro-backtrace for more info)
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error[E0277]: the trait bound `NonDiffable: Diffable` is not satisfied in `MyStructDiff<'__daft>`
37+
--> tests/fixtures/invalid/struct-field-not-diffable.rs:5:10
38+
|
39+
5 | #[derive(Diffable)]
40+
| ^^^^^^^^ within `MyStructDiff<'__daft>`, the trait `Diffable` is not implemented for `NonDiffable`
41+
|
42+
= help: the following other types implement trait `Diffable`:
43+
&'a T
44+
()
45+
(A, B)
46+
(A, B, C)
47+
(A, B, C, D)
48+
(A, B, C, D, E)
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(A, B, C, D, E, F)
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(A, B, C, D, E, F, G)
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and $N others
52+
note: required because it appears within the type `MyStructDiff<'__daft>`
53+
--> tests/fixtures/invalid/struct-field-not-diffable.rs:5:10
54+
|
55+
5 | #[derive(Diffable)]
56+
| ^^^^^^^^
57+
note: required by a bound in `daft::Diffable::Diff`
58+
--> $WORKSPACE/daft/src/diffable.rs
59+
|
60+
| / type Diff<'daft>
61+
| | where
62+
| | Self: 'daft;
63+
| |____________________^ required by this bound in `Diffable::Diff`
64+
= note: this error originates in the derive macro `Diffable` (in Nightly builds, run with -Z macro-backtrace for more info)
65+
66+
error[E0277]: the trait bound `NonDiffable: Diffable` is not satisfied in `MyStructDiff<'__daft>`
67+
--> tests/fixtures/invalid/struct-field-not-diffable.rs:5:10
68+
|
69+
5 | #[derive(Diffable)]
70+
| ^^^^^^^^ within `MyStructDiff<'__daft>`, the trait `Diffable` is not implemented for `NonDiffable`
71+
|
72+
= help: the following other types implement trait `Diffable`:
73+
&'a T
74+
()
75+
(A, B)
76+
(A, B, C)
77+
(A, B, C, D)
78+
(A, B, C, D, E)
79+
(A, B, C, D, E, F)
80+
(A, B, C, D, E, F, G)
81+
and $N others
82+
note: required because it appears within the type `MyStructDiff<'__daft>`
83+
--> tests/fixtures/invalid/struct-field-not-diffable.rs:5:10
84+
|
85+
5 | #[derive(Diffable)]
86+
| ^^^^^^^^
87+
= note: the return type of a function must have a statically known size
88+
= note: this error originates in the derive macro `Diffable` (in Nightly builds, run with -Z macro-backtrace for more info)

‎rust-toolchain.toml

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@@ -0,0 +1,8 @@
1+
# We use a specific toolchain revision to ensure our tests - which
2+
# occasionally depend on specific compiler output - remain stable
3+
# for all developers until the toolchain is explicitly advanced.
4+
# The intent is to keep this updated as new stable versions are relased.
5+
6+
[toolchain]
7+
channel = "1.85.0"
8+
profile = "default"

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