Rollup merge of #146495 - fmease:rustdoc-erase-doc-priv-items-attr, r=GuillaumeGomez

rustdoc: Erase `#![doc(document_private_items)]`

I just found out about the existence of `#![doc(document_private_items)]`. Apparently it was added by PR #50669 back in 2018 without any tests or docs as a replacement for some specific forms of the removed `#![doc(passes)]` / `#![doc(no_default_passes)]`.

However, rustc and rustdoc actually emit the deny-by-default lint `invalid_doc_attributes` for it (but if you allow it, the attribute does function)! To be more precise since PR #82708 (1.52, May 2021) which introduced lint `invalid_doc_attributes`, rust{,do}c has emitted a future-incompat warning for this attribute. And since PR #111505 (1.78, May 2024) that lint is deny by default. I presume nobody knew this attribute existed and thus it was never allowlisted.

Given the fact that since 2021 nobody has ever opened a ticket ([via](https://github.com/rust-lang/rust/issues?q=is%3Aissue+document_private_items)) complaining about the lint emission and the fact that GitHub code search doesn't yield any actual uses ([via](https://github.com/search?q=%2F%23%21%5C%5Bdoc%5C%28.*%3Fdocument_private_items%2F+language%3ARust&type=code&ref=advsearch)), I'm led to believe that nobody knows about and uses this attribute.

I don't find the existence of this attribute to be justified since in my view the flag `--document-private-items` is strictly superior: In most if not all cases, you don't want to "couple" your crate with this "mode" even if you gate it behind a cfg; instead, you most likely want to set this manually at invocation time, via a build config file like `.cargo/config.toml` or via a command runner like `just` I'd say.

Because of this I propose to wipe this attribute from existence. I don't believe it's worth cratering this (i.e., temporarily emitting a hard error for this attribute and running crater) given the fact that it's been undocumented since forever and led to a warning for years.

Author: Zalathar

compiler/rustc_passes/messages.ftl

@@ -219,7 +219,6 @@ passes_doc_test_unknown_passes =
     unknown `doc` attribute `{$path}`
     .note = `doc` attribute `{$path}` no longer functions; see issue #44136 <https://github.com/rust-lang/rust/issues/44136>
     .label = no longer functions
-    .help = you may want to use `doc(document_private_items)`
     .no_op_note = `doc({$path})` is now a no-op
 
 passes_doc_test_unknown_plugins =

compiler/rustc_passes/src/errors.rs

@@ -347,7 +347,6 @@ pub(crate) struct DocTestUnknownSpotlight {
 #[derive(LintDiagnostic)]
 #[diag(passes_doc_test_unknown_passes)]
 #[note]
-#[help]
 #[note(passes_no_op_note)]
 pub(crate) struct DocTestUnknownPasses {
     pub path: String,

compiler/rustc_span/src/symbol.rs

@@ -899,7 +899,6 @@ symbols! {
         doc_primitive,
         doc_spotlight,
         doctest,
-        document_private_items,
         dotdot: "..",
         dotdot_in_tuple_patterns,
         dotdoteq_in_patterns,

src/librustdoc/core.rs

@@ -416,14 +416,6 @@ pub(crate) fn run_global_ctxt(
         );
     }
 
-    // Process all of the crate attributes, extracting plugin metadata along
-    // with the passes which we are supposed to run.
-    for attr in krate.module.attrs.lists(sym::doc) {
-        if attr.is_word() && attr.has_name(sym::document_private_items) {
-            ctxt.render_options.document_private = true;
-        }
-    }
-
     info!("Executing passes");
 
     let mut visited = FxHashMap::default();

tests/rustdoc-ui/deprecated-attrs.rs

@@ -4,14 +4,12 @@
 //~^ ERROR unknown `doc` attribute `no_default_passes`
 //~| NOTE no longer functions
 //~| NOTE see issue #44136
-//~| HELP you may want to use `doc(document_private_items)`
 //~| NOTE `doc(no_default_passes)` is now a no-op
 //~| NOTE `#[deny(invalid_doc_attributes)]` on by default
 #![doc(passes = "collapse-docs unindent-comments")]
 //~^ ERROR unknown `doc` attribute `passes`
 //~| NOTE no longer functions
 //~| NOTE see issue #44136
-//~| HELP you may want to use `doc(document_private_items)`
 //~| NOTE `doc(passes)` is now a no-op
 #![doc(plugins = "xxx")]
 //~^ ERROR unknown `doc` attribute `plugins`

tests/rustdoc-ui/deprecated-attrs.stderr

@@ -10,22 +10,20 @@ LL | #![doc(no_default_passes)]
    |        ^^^^^^^^^^^^^^^^^ no longer functions
    |
    = note: `doc` attribute `no_default_passes` no longer functions; see issue #44136 <https://github.com/rust-lang/rust/issues/44136>
-   = help: you may want to use `doc(document_private_items)`
    = note: `doc(no_default_passes)` is now a no-op
    = note: `#[deny(invalid_doc_attributes)]` on by default
 
 error: unknown `doc` attribute `passes`
-  --> $DIR/deprecated-attrs.rs:10:8
+  --> $DIR/deprecated-attrs.rs:9:8
    |
 LL | #![doc(passes = "collapse-docs unindent-comments")]
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ no longer functions
    |
    = note: `doc` attribute `passes` no longer functions; see issue #44136 <https://github.com/rust-lang/rust/issues/44136>
-   = help: you may want to use `doc(document_private_items)`
    = note: `doc(passes)` is now a no-op
 
 error: unknown `doc` attribute `plugins`
-  --> $DIR/deprecated-attrs.rs:16:8
+  --> $DIR/deprecated-attrs.rs:14:8
    |
 LL | #![doc(plugins = "xxx")]
    |        ^^^^^^^^^^^^^^^ no longer functions