Rollup merge of #115869 - ferrocene:pa-fix-tests-cargo-remap, r=compiler-errors

Avoid blessing cargo deps's source code in ui tests

Before this PR, the source code of dependencies was included in UI test error messages whenever possible. Unfortunately, "whenever possible" means in some cases the source code wouldn't be injected, resulting in a test failure.

One such case is when `$CARGO_HOME` is remapped to something that is not present on disk [^1]. As the remapped path doesn't exist on disk, the source code wouldn't be showed in `tests/ui/issues/issue-21763.rs`:

```diff
    = note: required for `hashbrown::raw::RawTable<(Rc<()>, Rc<()>)>` to implement `Send`
 note: required because it appears within the type `HashMap<Rc<()>, Rc<()>, RandomState>`
   --> $HASHBROWN_SRC_LOCATION
-   |
-LL | pub struct HashMap<K, V, S = DefaultHashBuilder, A: Allocator + Clone = Global> {
-   |            ^^^^^^^
 note: required because it appears within the type `HashMap<Rc<()>, Rc<()>>`
   --> $SRC_DIR/std/src/collections/hash/map.rs:LL:COL
 note: required by a bound in `foo`
```

This PR fixes the problem by always hiding dependencies source code in the error messages generated during UI tests. This is implemented with a new internal flag, `-Z ignore-directory-in-diagnostics-source-blocks=$path`, which compiletest passes during UI tests. Once this is merged, remapping the Cargo home will be supported.

This PR is best reviewed commit-by-commit.

[^1]: After being puzzled for a bit, I discovered why this never impacted `rust-lang/rust`: we don't remap `$CARGO_HOME` :sweat_smile:. Instead, we set `$CARGO_HOME` to `/cargo` in CI, which sort-of-but-not-really achieves the same effect.

2 files changed, 10 insertions, 2 deletions

diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
index 73fd7965895..f2c8f0bc198 100644
--- a/compiler/rustc_session/src/options.rs
+++ b/compiler/rustc_session/src/options.rs
@@ -1536,6 +1536,8 @@ options! {
         "generate human-readable, predictable names for codegen units (default: no)"),
     identify_regions: bool = (false, parse_bool, [UNTRACKED],
         "display unnamed regions as `'<id>`, using a non-ident unique id (default: no)"),
+    ignore_directory_in_diagnostics_source_blocks: Vec<String> = (Vec::new(), parse_string_push, [UNTRACKED],
+        "do not display the source code block in diagnostics for files in the directory"),
     incremental_ignore_spans: bool = (false, parse_bool, [TRACKED],
         "ignore spans during ICH computation -- used for testing (default: no)"),
     incremental_info: bool = (false, parse_bool, [UNTRACKED],
diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
index 9bff9017881..86f4e7b48da 100644
--- a/compiler/rustc_session/src/session.rs
+++ b/compiler/rustc_session/src/session.rs
@@ -1295,7 +1295,10 @@ fn default_emitter(
                     .diagnostic_width(sopts.diagnostic_width)
                     .macro_backtrace(macro_backtrace)
                     .track_diagnostics(track_diagnostics)
-                    .terminal_url(terminal_url);
+                    .terminal_url(terminal_url)
+                    .ignored_directories_in_source_blocks(
+                        sopts.unstable_opts.ignore_directory_in_diagnostics_source_blocks.clone(),
+                    );
                 Box::new(emitter.ui_testing(sopts.unstable_opts.ui_testing))
             }
         }
@@ -1312,7 +1315,10 @@ fn default_emitter(
                 track_diagnostics,
                 terminal_url,
             )
-            .ui_testing(sopts.unstable_opts.ui_testing),
+            .ui_testing(sopts.unstable_opts.ui_testing)
+            .ignored_directories_in_source_blocks(
+                sopts.unstable_opts.ignore_directory_in_diagnostics_source_blocks.clone(),
+            ),
         ),
     }
 }