Rollup merge of #79877 - bstrie:depinfut, r=oli-obk

Allow `since="TBD"` for rustc_deprecated

Closes #78381.

This PR only affects `#[rustc_deprecated]`, not `#[deprecated]`, so there is no effect on any stable language feature.

Likewise this PR only implements `since="TBD"`, it does not actually tag any library functions with it, so there is no effect on any stable API.

Overview of changes:

* `rustc_middle/stability.rs`:
    * change `deprecation_in_effect` function to return `false` when `since="TBD"`
    * tidy up the compiler output when a deprecated item has `since="TBD"`
* `rustc_passes/stability.rs`:
    * allow `since="TBD"` to pass the sanity check for stable_version < deprecated_version
    * refactor the "invalid stability version" and "invalid deprecation version" error into separate errors
* rustdoc: make `since="TBD"` message on a deprecated item's page match the command-line deprecation output
* tests:
    * test rustdoc output
    * test that the `deprecated_in_future` lint fires when `since="TBD"`
    * test the new "invalid deprecation version" error message

6 files changed, 47 insertions, 14 deletions

diff --git a/src/librustdoc/html/render/mod.rs b/src/librustdoc/html/render/mod.rs
index 88c5e94c276..00294878fe5 100644
--- a/src/librustdoc/html/render/mod.rs
+++ b/src/librustdoc/html/render/mod.rs
@@ -2279,7 +2279,11 @@ fn short_item_info(item: &clean::Item, cx: &Context, parent: Option<&clean::Item
         let mut message = if let Some(since) = since {
             let since = &since.as_str();
             if !stability::deprecation_in_effect(is_since_rustc_version, Some(since)) {
-                format!("Deprecating in {}", Escape(since))
+                if *since == "TBD" {
+                    format!("Deprecating in a future Rust version")
+                } else {
+                    format!("Deprecating in {}", Escape(since))
+                }
             } else {
                 format!("Deprecated since {}", Escape(since))
             }
diff --git a/src/test/rustdoc/rustc_deprecated-future.rs b/src/test/rustdoc/rustc_deprecated-future.rs
index 3133775706b..95a767a8329 100644
--- a/src/test/rustdoc/rustc_deprecated-future.rs
+++ b/src/test/rustdoc/rustc_deprecated-future.rs
@@ -4,8 +4,16 @@
 
 // @has rustc_deprecated_future/index.html '//*[@class="stab deprecated"]' \
 //      'Deprecation planned'
-// @has rustc_deprecated_future/struct.S.html '//*[@class="stab deprecated"]' \
+// @has rustc_deprecated_future/struct.S1.html '//*[@class="stab deprecated"]' \
 //      'Deprecating in 99.99.99: effectively never'
 #[rustc_deprecated(since = "99.99.99", reason = "effectively never")]
 #[stable(feature = "rustc_deprecated-future-test", since = "1.0.0")]
-pub struct S;
+pub struct S1;
+
+// @has rustc_deprecated_future/index.html '//*[@class="stab deprecated"]' \
+//      'Deprecation planned'
+// @has rustc_deprecated_future/struct.S2.html '//*[@class="stab deprecated"]' \
+//      'Deprecating in a future Rust version: literally never'
+#[rustc_deprecated(since = "TBD", reason = "literally never")]
+#[stable(feature = "rustc_deprecated-future-test", since = "1.0.0")]
+pub struct S2;
diff --git a/src/test/ui/deprecation/rustc_deprecation-in-future.rs b/src/test/ui/deprecation/rustc_deprecation-in-future.rs
index 6a619bcc49c..11f7960b757 100644
--- a/src/test/ui/deprecation/rustc_deprecation-in-future.rs
+++ b/src/test/ui/deprecation/rustc_deprecation-in-future.rs
@@ -8,8 +8,13 @@
 
 #[rustc_deprecated(since = "99.99.99", reason = "effectively never")]
 #[stable(feature = "rustc_deprecation-in-future-test", since = "1.0.0")]
-pub struct S;
+pub struct S1;
+
+#[rustc_deprecated(since = "TBD", reason = "literally never")]
+#[stable(feature = "rustc_deprecation-in-future-test", since = "1.0.0")]
+pub struct S2;
 
 fn main() {
-    let _ = S; //~ ERROR use of unit struct `S` that will be deprecated in future version 99.99.99: effectively never
+    let _ = S1; //~ ERROR use of unit struct `S1` that will be deprecated in future version 99.99.99: effectively never
+    let _ = S2; //~ ERROR use of unit struct `S2` that will be deprecated in a future Rust version: literally never
 }
diff --git a/src/test/ui/deprecation/rustc_deprecation-in-future.stderr b/src/test/ui/deprecation/rustc_deprecation-in-future.stderr
index e4f50d10dad..b5a7dd3c28d 100644
--- a/src/test/ui/deprecation/rustc_deprecation-in-future.stderr
+++ b/src/test/ui/deprecation/rustc_deprecation-in-future.stderr
@@ -1,8 +1,8 @@
-error: use of unit struct `S` that will be deprecated in future version 99.99.99: effectively never
-  --> $DIR/rustc_deprecation-in-future.rs:14:13
+error: use of unit struct `S1` that will be deprecated in future version 99.99.99: effectively never
+  --> $DIR/rustc_deprecation-in-future.rs:18:13
    |
-LL |     let _ = S;
-   |             ^
+LL |     let _ = S1;
+   |             ^^
    |
 note: the lint level is defined here
   --> $DIR/rustc_deprecation-in-future.rs:3:9
@@ -10,5 +10,11 @@ note: the lint level is defined here
 LL | #![deny(deprecated_in_future)]
    |         ^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to previous error
+error: use of unit struct `S2` that will be deprecated in a future Rust version: literally never
+  --> $DIR/rustc_deprecation-in-future.rs:19:13
+   |
+LL |     let _ = S2;
+   |             ^^
+
+error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/stability-attribute/stability-attribute-sanity.rs b/src/test/ui/stability-attribute/stability-attribute-sanity.rs
index abd603b356e..0c40f8ae1c6 100644
--- a/src/test/ui/stability-attribute/stability-attribute-sanity.rs
+++ b/src/test/ui/stability-attribute/stability-attribute-sanity.rs
@@ -63,7 +63,11 @@ fn multiple3() { }
 #[rustc_const_unstable(feature = "c", issue = "none")]
 #[rustc_const_unstable(feature = "d", issue = "none")] //~ ERROR multiple stability levels
 pub const fn multiple4() { }
-//~^ ERROR Invalid stability or deprecation version found
+//~^ ERROR Invalid stability version found
+
+#[stable(feature = "a", since = "1.0.0")]
+#[rustc_deprecated(since = "invalid", reason = "text")]
+fn invalid_deprecation_version() {} //~ ERROR Invalid deprecation version found
 
 #[rustc_deprecated(since = "a", reason = "text")]
 fn deprecated_without_unstable_or_stable() { }
diff --git a/src/test/ui/stability-attribute/stability-attribute-sanity.stderr b/src/test/ui/stability-attribute/stability-attribute-sanity.stderr
index 97089f7df52..ee9a93359f0 100644
--- a/src/test/ui/stability-attribute/stability-attribute-sanity.stderr
+++ b/src/test/ui/stability-attribute/stability-attribute-sanity.stderr
@@ -96,19 +96,25 @@ error[E0544]: multiple stability levels
 LL | #[rustc_const_unstable(feature = "d", issue = "none")]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: Invalid stability or deprecation version found
+error: Invalid stability version found
   --> $DIR/stability-attribute-sanity.rs:65:1
    |
 LL | pub const fn multiple4() { }
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
+error: Invalid deprecation version found
+  --> $DIR/stability-attribute-sanity.rs:70:1
+   |
+LL | fn invalid_deprecation_version() {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
 error[E0549]: rustc_deprecated attribute must be paired with either stable or unstable attribute
-  --> $DIR/stability-attribute-sanity.rs:68:1
+  --> $DIR/stability-attribute-sanity.rs:72:1
    |
 LL | #[rustc_deprecated(since = "a", reason = "text")]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 18 previous errors
+error: aborting due to 19 previous errors
 
 Some errors have detailed explanations: E0539, E0541, E0546, E0550.
 For more information about an error, try `rustc --explain E0539`.