rustc_marker_type built in attribute created to have certain marker types not trigger dead code warnings from clippy

[asder8215]

This PR fixes the issue on PhantomPinned triggering field is never read warning by clippy through a built in attribute called rustc_marker_type.

A few questions I have are:

• If a built in attribute approach is okay to use here, should I extend this attribute to all the other Phantom* types?
• Currently, I have every change I made into 1 commit. Should I separate the changes I made for compiler and the changes I made for clippy into different commits?
• Does a built in attribute like this have uses outside of being internal to the standard library? I'm wondering if people create marker types and wish to not have dead code warnings on them.

Note: This is my first time contributing to the compiler side of Rust repos, so I'm unsure if I'm doing anything wrong with making a built in attribute. I'm just going based off my intuition from go to references in my IDE on what everything is doing.

cc @clarfonthey

[rustbot]

Some changes occurred in compiler/rustc_hir/src/attrs

cc @jdonszelmann, @JonathanBrouwer

Some changes occurred in compiler/rustc_passes/src/check_attr.rs

cc @jdonszelmann, @JonathanBrouwer

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

[rustbot]

r? @davidtwco

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[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[rust-log-analyzer]

The job x86_64-gnu-tools failed! Check out the build log: (web) (plain enhanced) (plain)

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

tests/ui/size_of_in_element_count/functions.rs ... ok
tests/ui/crashes/third-party/conf_allowlisted.rs ... ok

FAILED TEST: tests/ui/missing_fields_in_debug.rs
command: CLIPPY_CONF_DIR="tests" RUSTC_ICE="0" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/release/clippy-driver" "--error-format=json" "--emit=metadata" "-Aunused" "-Ainternal_features" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Dwarnings" "-Ldependency=/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/release/deps" "--sysroot=/checkout/obj/build/x86_64-unknown-linux-gnu/stage2" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/ui_test/0/tests/ui" "tests/ui/missing_fields_in_debug.rs" "--extern" "futures=/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/debug/deps/libfutures-fbb2c78a4397bb08.rlib" "--extern" "futures=/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/debug/deps/libfutures-fbb2c78a4397bb08.rmeta" "--extern" "itertools=/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/debug/deps/libitertools-08cb6de3a10b25d1.rlib" "--extern" "itertools=/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/debug/deps/libitertools-08cb6de3a10b25d1.rmeta" "--extern" "libc=/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/debug/deps/liblibc-ac3195ae9071a567.rlib" "--extern" "libc=/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/debug/deps/liblibc-ac3195ae9071a567.rmeta" "--extern" "parking_lot=/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/debug/deps/libparking_lot-cb20139ff7bab978.rlib" "--extern" "parking_lot=/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/debug/deps/libparking_lot-cb20139ff7bab978.rmeta" "--extern" "quote=/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/debug/deps/libquote-d52f64f9beb2b3e9.rlib" "--extern" "quote=/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/debug/deps/libquote-d52f64f9beb2b3e9.rmeta" "--extern" "regex=/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/debug/deps/libregex-099fa7d611da1769.rlib" "--extern" "regex=/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/debug/deps/libregex-099fa7d611da1769.rmeta" "--extern" "serde=/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/debug/deps/libserde-cc2552a331d3edc6.rlib" "--extern" "serde=/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/debug/deps/libserde-cc2552a331d3edc6.rmeta" "--extern" "syn=/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/debug/deps/libsyn-6fe3ac6a29af0bce.rlib" "--extern" "syn=/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/debug/deps/libsyn-6fe3ac6a29af0bce.rmeta" "--extern" "tokio=/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/debug/deps/libtokio-115c8b7669715635.rlib" "--extern" "tokio=/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/debug/deps/libtokio-115c8b7669715635.rmeta" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/debug/deps" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/debug/deps" "--edition" "2024"

error: actual output differed from expected
Execute `./x test src/tools/clippy --bless` to update `tests/ui/missing_fields_in_debug.stderr` to the actual output
--- tests/ui/missing_fields_in_debug.stderr
+++ <stderr output>
---
-error: aborting due to 3 previous errors
+error: manual `Debug` impl does not include all fields
+  --> tests/ui/missing_fields_in_debug.rs:190:1
+   |
+LL | / impl fmt::Debug for WithPDPP {
+LL | |     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+LL | |         f.debug_struct("WithPD")
+LL | |             .field("a", &self.a)
+...  |
+LL | | }
+   | |_^
+   |
+note: this field is unused
+  --> tests/ui/missing_fields_in_debug.rs:186:5
+   |
+LL |     c: PhantomPinned,
+   |     ^^^^^^^^^^^^^^^^
+note: this field is unused
+  --> tests/ui/missing_fields_in_debug.rs:187:5
+   |
+LL |     d: PhantomData<String>,
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+   = help: consider including all fields in this `Debug` impl
+   = help: consider calling `.finish_non_exhaustive()` if you intend to ignore fields
 
+error: aborting due to 4 previous errors
---
   |     ^^^^^^^^^^^^^^^
note: this field is unused
  --> tests/ui/missing_fields_in_debug.rs:31:5
   |
LL |     hidden4: ((((u8), u16), u32), u64),
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   = help: consider including all fields in this `Debug` impl
   = help: consider calling `.finish_non_exhaustive()` if you intend to ignore fields

error: manual `Debug` impl does not include all fields
##[error]  --> tests/ui/missing_fields_in_debug.rs:97:1
   |
LL | / impl fmt::Debug for MultiExprDebugImpl {
LL | |
LL | |
LL | |     fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
...  |
LL | | }
   | |_^
   |
note: this field is unused
---

error: manual `Debug` impl does not include all fields
##[error]  --> tests/ui/missing_fields_in_debug.rs:190:1
   |
LL | / impl fmt::Debug for WithPDPP {
LL | |     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
LL | |         f.debug_struct("WithPD")
LL | |             .field("a", &self.a)
...  |
LL | | }
   | |_^
   |
note: this field is unused
  --> tests/ui/missing_fields_in_debug.rs:186:5
   |
LL |     c: PhantomPinned,
   |     ^^^^^^^^^^^^^^^^
note: this field is unused
  --> tests/ui/missing_fields_in_debug.rs:187:5
   |
LL |     d: PhantomData<String>,
   |     ^^^^^^^^^^^^^^^^^^^^^^
   = help: consider including all fields in this `Debug` impl
   = help: consider calling `.finish_non_exhaustive()` if you intend to ignore fields

error: aborting due to 4 previous errors



error: there was 1 unmatched diagnostic
##[error]   --> tests/ui/missing_fields_in_debug.rs:190:1
    |
190 | / impl fmt::Debug for WithPDPP {
191 | |     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
...   |
196 | |     }
197 | | }
    | |_^ Error[clippy::missing_fields_in_debug]: manual `Debug` impl does not include all fields
    |

full stderr:
error: manual `Debug` impl does not include all fields
##[error]  --> tests/ui/missing_fields_in_debug.rs:14:1
---
   |     ^^^^^^^^^^^^^^^
note: this field is unused
  --> tests/ui/missing_fields_in_debug.rs:31:5
   |
LL |     hidden4: ((((u8), u16), u32), u64),
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   = help: consider including all fields in this `Debug` impl
   = help: consider calling `.finish_non_exhaustive()` if you intend to ignore fields

error: manual `Debug` impl does not include all fields
##[error]  --> tests/ui/missing_fields_in_debug.rs:97:1
   |
LL | / impl fmt::Debug for MultiExprDebugImpl {
LL | |
LL | |
LL | |     fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
...  |
LL | | }
   | |_^
   |
note: this field is unused
---

error: manual `Debug` impl does not include all fields
##[error]  --> tests/ui/missing_fields_in_debug.rs:190:1
   |
LL | / impl fmt::Debug for WithPDPP {
LL | |     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
LL | |         f.debug_struct("WithPD")
LL | |             .field("a", &self.a)
...  |
LL | | }
   | |_^
   |
note: this field is unused
  --> tests/ui/missing_fields_in_debug.rs:186:5
   |
LL |     c: PhantomPinned,
   |     ^^^^^^^^^^^^^^^^
note: this field is unused
  --> tests/ui/missing_fields_in_debug.rs:187:5
   |
LL |     d: PhantomData<String>,
   |     ^^^^^^^^^^^^^^^^^^^^^^
   = help: consider including all fields in this `Debug` impl
   = help: consider calling `.finish_non_exhaustive()` if you intend to ignore fields

error: aborting due to 4 previous errors