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test: add more tests and const generics documentation
Fill test coverage gaps identified during code review: - `trybuild`: verify error messages for missing Facet derive, non-Debug type params, and const generics (documenting the limitation) - `insta`: snapshot tests for exact Debug output format verification across structs, enums, tuple structs, and nested types - Bump `facet` dev-dep to 0.44
1 parent 8392ae0 commit 99f5eca

18 files changed

Lines changed: 345 additions & 1 deletion

‎Cargo.toml‎

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@@ -27,7 +27,9 @@ quote = "1.0"
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facet-macros-parse = "0.31"
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[dev-dependencies]
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facet = { version = "0.43.2", features = ["reflect"] }
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facet = { version = "0.44", features = ["reflect"] }
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insta = "1"
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trybuild = { version = "1", features = ["diff"] }
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[[example]]
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name = "enum_example"

‎tests/compile_fail/const_generic.rs‎

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/// Const generics are not supported.
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/// Both `Facet` and `SafeDebug` fail on const generic parameters.
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/// Facet's derive rejects `const N: usize` outright, and SafeDebug's
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/// string-based generics parser produces unparsable tokens.
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use facet::Facet;
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use safe_debug::SafeDebug;
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#[derive(Facet, SafeDebug)]
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struct FixedBuffer<const N: usize> {
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#[facet(sensitive)]
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data: [u8; N],
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label: String,
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}
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fn main() {
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let buf: FixedBuffer<4> = FixedBuffer {
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data: [1, 2, 3, 4],
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label: "test".to_string(),
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};
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println!("{:?}", buf);
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}

‎tests/compile_fail/const_generic.stderr‎

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error: unexpected `const` parameter declaration
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--> tests/compile_fail/const_generic.rs:9:20
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|
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9 | struct FixedBuffer<const N: usize> {
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| ^^^^^^^^^^^^^^ expected a `const` expression, not a parameter declaration
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error: expected one of `#`, `{`, lifetime, or type, found keyword `const`
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--> tests/compile_fail/const_generic.rs:8:17
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|
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8 | #[derive(Facet, SafeDebug)]
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| ^^^^^^^^^ expected one of `#`, `{`, lifetime, or type
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|
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= note: this error originates in the derive macro `SafeDebug` (in Nightly builds, run with -Z macro-backtrace for more info)
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error: proc-macro derive produced unparsable tokens
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--> tests/compile_fail/const_generic.rs:8:17
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|
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8 | #[derive(Facet, SafeDebug)]
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| ^^^^^^^^^
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error[E0277]: `FixedBuffer<4>` doesn't implement `std::fmt::Debug`
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--> tests/compile_fail/const_generic.rs:20:22
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|
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20 | println!("{:?}", buf);
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| ---- ^^^ `FixedBuffer<4>` cannot be formatted using `{:?}` because it doesn't implement `std::fmt::Debug`
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| |
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| required by this formatting parameter
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|
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= help: the trait `std::fmt::Debug` is not implemented for `FixedBuffer<4>`
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= note: add `#[derive(Debug)]` to `FixedBuffer<4>` or manually `impl std::fmt::Debug for FixedBuffer<4>`
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= note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
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help: consider annotating `FixedBuffer<4>` with `#[derive(Debug)]`
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|
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9 + #[derive(Debug)]
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10 | struct FixedBuffer<const N: usize> {
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|

‎tests/compile_fail/missing_facet_derive.rs‎

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/// Deriving SafeDebug without Facet should produce a helpful error.
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use safe_debug::SafeDebug;
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#[derive(SafeDebug)]
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struct MissingFacet {
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name: String,
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#[facet(sensitive)]
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secret: String,
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}
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fn main() {}

‎tests/compile_fail/missing_facet_derive.stderr‎

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error: cannot find attribute `facet` in this scope
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--> tests/compile_fail/missing_facet_derive.rs:7:7
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|
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7 | #[facet(sensitive)]
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| ^^^^^
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|
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= note: `facet` is in scope, but it is a crate, not an attribute
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error[E0599]: no associated item named `SHAPE` found for struct `MissingFacet` in the current scope
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--> tests/compile_fail/missing_facet_derive.rs:4:10
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|
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4 | #[derive(SafeDebug)]
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| ^^^^^^^^^ associated item not found in `MissingFacet`
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5 | struct MissingFacet {
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| ------------------- associated item `SHAPE` not found for this struct
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|
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= help: items from traits can only be used if the trait is implemented and in scope
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= note: the following trait defines an item `SHAPE`, perhaps you need to implement it:
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candidate #1: `Facet`
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= note: this error originates in the derive macro `SafeDebug` (in Nightly builds, run with -Z macro-backtrace for more info)

‎tests/compile_fail/non_debug_type_param.rs‎

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/// A generic type parameter that doesn't implement Debug should fail to compile.
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use facet::Facet;
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use safe_debug::SafeDebug;
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struct NotDebug;
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#[derive(Facet, SafeDebug)]
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struct Container<T> {
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value: T,
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}
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fn main() {
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let c = Container { value: NotDebug };
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// This should fail because NotDebug doesn't implement Debug
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println!("{:?}", c);
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}

‎tests/compile_fail/non_debug_type_param.stderr‎

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error[E0277]: `NotDebug` doesn't implement `std::fmt::Debug`
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--> tests/compile_fail/non_debug_type_param.rs:15:22
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|
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15 | println!("{:?}", c);
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| ---- ^ `NotDebug` cannot be formatted using `{:?}` because it doesn't implement `std::fmt::Debug`
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| |
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| required by this formatting parameter
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|
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= help: the trait `std::fmt::Debug` is not implemented for `NotDebug`
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= note: add `#[derive(Debug)]` to `NotDebug` or manually `impl std::fmt::Debug for NotDebug`
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help: the trait `std::fmt::Debug` is implemented for `Container<T>`
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--> tests/compile_fail/non_debug_type_param.rs:7:17
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|
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7 | #[derive(Facet, SafeDebug)]
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| ^^^^^^^^^
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note: required for `Container<NotDebug>` to implement `std::fmt::Debug`
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--> tests/compile_fail/non_debug_type_param.rs:7:17
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|
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7 | #[derive(Facet, SafeDebug)]
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| ^^^^^^^^^ unsatisfied trait bound introduced in this `derive` macro
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= note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the derive macro `SafeDebug` (in Nightly builds, run with -Z macro-backtrace for more info)
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help: consider annotating `NotDebug` with `#[derive(Debug)]`
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|
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5 + #[derive(Debug)]
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6 | struct NotDebug;
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|
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error[E0277]: the trait bound `for<'__facet> NotDebug: Facet<'__facet>` is not satisfied
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--> tests/compile_fail/non_debug_type_param.rs:15:22
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|
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15 | println!("{:?}", c);
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| ---- ^ unsatisfied trait bound
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| |
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| required by this formatting parameter
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|
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help: the trait `for<'__facet> Facet<'__facet>` is not implemented for `NotDebug`
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--> tests/compile_fail/non_debug_type_param.rs:5:1
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|
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5 | struct NotDebug;
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| ^^^^^^^^^^^^^^^
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= help: the following other types implement trait `Facet<'facet>`:
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`&'a T` implements `Facet<'a>`
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`&'a mut T` implements `Facet<'a>`
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`()` implements `Facet<'_>`
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`(T0, T1)` implements `Facet<'a>`
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`(T0, T1, T2)` implements `Facet<'a>`
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`(T0, T1, T2, T3)` implements `Facet<'a>`
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`(T0,)` implements `Facet<'a>`
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`*const T` implements `Facet<'a>`
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and $N others
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note: required for `Container<NotDebug>` to implement `std::fmt::Debug`
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--> tests/compile_fail/non_debug_type_param.rs:7:17
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|
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7 | #[derive(Facet, SafeDebug)]
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| ^^^^^^^^^ unsatisfied trait bound introduced in this `derive` macro
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= note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the derive macro `SafeDebug` (in Nightly builds, run with -Z macro-backtrace for more info)

‎tests/compile_fail_tests.rs‎

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#[test]
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fn compile_fail() {
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let t = trybuild::TestCases::new();
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t.compile_fail("tests/compile_fail/*.rs");
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}

‎tests/snapshot_tests.rs‎

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use facet::Facet;
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use safe_debug::SafeDebug;
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// --- Type definitions for snapshot tests ---
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#[derive(Facet, SafeDebug)]
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struct PatientRecord {
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id: String,
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name: String,
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#[facet(sensitive)]
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ssn: String,
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#[facet(sensitive)]
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medical_history: String,
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}
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#[derive(Facet, SafeDebug)]
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struct TupleRecord(String, #[facet(sensitive)] String, i32);
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#[derive(Facet, SafeDebug)]
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#[repr(C)]
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enum ApiResponse {
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Success { code: u16, data: String },
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Error {
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code: u16,
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#[facet(sensitive)]
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details: String,
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},
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Pending,
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Token(#[facet(sensitive)] String),
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}
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#[derive(Facet, SafeDebug)]
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struct Inner {
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public_data: String,
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#[facet(sensitive)]
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secret_data: String,
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}
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#[derive(Facet, SafeDebug)]
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struct Outer {
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id: u32,
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inner: Inner,
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}
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// --- Snapshot tests ---
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#[test]
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fn snapshot_named_struct() {
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let record = PatientRecord {
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id: "P-12345".to_string(),
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name: "Jane Doe".to_string(),
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ssn: "123-45-6789".to_string(),
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medical_history: "Chronic condition notes".to_string(),
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};
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insta::assert_snapshot!(format!("{:?}", record));
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}
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#[test]
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fn snapshot_named_struct_pretty() {
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let record = PatientRecord {
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id: "P-12345".to_string(),
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name: "Jane Doe".to_string(),
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ssn: "123-45-6789".to_string(),
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medical_history: "Chronic condition notes".to_string(),
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};
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insta::assert_snapshot!(format!("{:#?}", record));
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}
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#[test]
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fn snapshot_tuple_struct() {
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let record = TupleRecord("visible".to_string(), "secret-token".to_string(), 42);
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insta::assert_snapshot!(format!("{:?}", record));
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}
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#[test]
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fn snapshot_enum_struct_variant() {
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let success = ApiResponse::Success {
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code: 200,
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data: "OK".to_string(),
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};
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insta::assert_snapshot!("enum_success", format!("{:?}", success));
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let error = ApiResponse::Error {
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code: 500,
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details: "password leaked in stack trace".to_string(),
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};
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insta::assert_snapshot!("enum_error_redacted", format!("{:?}", error));
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}
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#[test]
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fn snapshot_enum_unit_and_tuple_variants() {
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let pending = ApiResponse::Pending;
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insta::assert_snapshot!("enum_pending", format!("{:?}", pending));
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let token = ApiResponse::Token("secret-bearer-token".to_string());
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insta::assert_snapshot!("enum_token_redacted", format!("{:?}", token));
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}
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#[test]
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fn snapshot_nested_struct() {
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let data = Outer {
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id: 999,
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inner: Inner {
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public_data: "visible-info".to_string(),
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secret_data: "classified-payload".to_string(),
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},
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};
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insta::assert_snapshot!(format!("{:?}", data));
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}
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#[test]
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fn snapshot_nested_struct_pretty() {
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let data = Outer {
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id: 999,
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inner: Inner {
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public_data: "visible-info".to_string(),
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secret_data: "classified-payload".to_string(),
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},
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};
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insta::assert_snapshot!(format!("{:#?}", data));
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}

‎tests/snapshots/snapshot_tests__enum_error_redacted.snap‎

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---
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source: tests/snapshot_tests.rs
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expression: "format!(\"{:?}\", error)"
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---
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ApiResponse::Error { code: 500, details: "[REDACTED]" }

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