Rollup merge of #93661 - ehuss:add-missing-rustc-arg-docs, r=estebank,Mark-Simulacrum

Add missing rustc arg docs

Add documentation for recently added rustc args

`-C symbol-mangling-version` was stabilized in #90128.
`--json=future-incompat` was stabilized in #91535.

src/doc/rustc/src/codegen-options/index.md

@@ -550,6 +550,21 @@ Supported values for this option are:
 - `symbols` - same as `debuginfo`, but the rest of the symbol table section is
   stripped as well if the linker supports it.
 
+## symbol-mangling-version
+
+This option controls the [name mangling] format for encoding Rust item names
+for the purpose of generating object code and linking.
+
+Supported values for this option are:
+
+* `v0` — The "v0" mangling scheme. The specific format is not specified at
+  this time.
+
+The default if not specified will use a compiler-chosen default which may
+change in the future.
+
+[name mangling]: https://en.wikipedia.org/wiki/Name_mangling
+
 ## target-cpu
 
 This instructs `rustc` to generate code specifically for a particular processor.

src/doc/rustc/src/command-line-arguments.md

@@ -408,6 +408,9 @@ to customize the output:
   argument](#option-emit), and as soon as the artifact is available on the
   filesystem a notification will be emitted.
 
+- `future-incompat` - includes a JSON message that contains a report if the
+  crate contains any code that may fail to compile in the future.
+
 Note that it is invalid to combine the `--json` argument with the
 [`--color`](#option-color) argument, and it is required to combine `--json`
 with `--error-format=json`.

src/doc/rustc/src/json.md

@@ -229,6 +229,32 @@ flag][option-emit] documentation.
 }
 ```
 
+## Future-incompatible reports
+
+If the [`--json=future-incompat`][option-json] flag is used, then a separate
+JSON structure will be emitted if the crate may stop compiling in the future.
+This contains diagnostic information about the particular warnings that may be
+turned into a hard error in the future. This will include the diagnostic
+information, even if the diagnostics have been suppressed (such as with an
+`#[allow]` attribute or the `--cap-lints` option).
+
+```javascript
+{
+    /* An array of objects describing a warning that will become a hard error
+       in the future.
+    */
+    "future_incompat_report":
+    [
+        {
+            /* A diagnostic structure as defined in
+               https://doc.rust-lang.org/rustc/json.html#diagnostics
+            */
+            "diagnostic": {...},
+        }
+    ]
+}
+```
+
 [option-emit]: command-line-arguments.md#option-emit
 [option-error-format]: command-line-arguments.md#option-error-format
 [option-json]: command-line-arguments.md#option-json