new unstable option: -Zwrite-long-types-to-disk

This option guards the logic of writing long type names in files and
instead using short forms in error messages in rustc_middle/ty/error
behind a flag. The main motivation for this change is to disable this
behaviour when running ui tests.

This logic can be triggered by running tests in a directory that has a
long enough path, e.g. /my/very-long-path/where/rust-codebase/exists/

This means ui tests can fail depending on how long the path to their
file is.

Some ui tests actually rely on this behaviour for their assertions,
so for those we enable the flag manually.

Author: mdibaiee

compiler/rustc_interface/src/tests.rs

@@ -738,6 +738,7 @@ fn test_unstable_options_tracking_hash() {
     untracked!(unstable_options, true);
     untracked!(validate_mir, true);
     untracked!(verbose, true);
+    untracked!(write_long_types_to_disk, true);
     // tidy-alphabetical-end
 
     macro_rules! tracked {

compiler/rustc_middle/src/ty/error.rs

@@ -339,12 +339,17 @@ impl<'tcx> TyCtxt<'tcx> {
     }
 
     pub fn short_ty_string(self, ty: Ty<'tcx>) -> (String, Option<PathBuf>) {
-        let width = self.sess.diagnostic_width();
-        let length_limit = width.saturating_sub(30);
         let regular = FmtPrinter::new(self, hir::def::Namespace::TypeNS)
             .pretty_print_type(ty)
             .expect("could not write to `String`")
             .into_buffer();
+
+        if !self.sess.opts.unstable_opts.write_long_types_to_disk {
+            return (regular, None);
+        }
+
+        let width = self.sess.diagnostic_width();
+        let length_limit = width.saturating_sub(30);
         if regular.len() <= width {
             return (regular, None);
         }

compiler/rustc_session/src/options.rs

@@ -1875,6 +1875,8 @@ written to standard error output)"),
         Requires `-Clto[=[fat,yes]]`"),
     wasi_exec_model: Option<WasiExecModel> = (None, parse_wasi_exec_model, [TRACKED],
         "whether to build a wasi command or reactor"),
+    write_long_types_to_disk: bool = (true, parse_bool, [UNTRACKED],
+        "whether long type names should be written to files instead of being printed in errors"),
     // tidy-alphabetical-end
 
     // If you add a new option, please update:

src/tools/compiletest/src/runtest.rs

@@ -2330,6 +2330,7 @@ impl<'test> TestCx<'test> {
                 // Hide line numbers to reduce churn
                 rustc.arg("-Zui-testing");
                 rustc.arg("-Zdeduplicate-diagnostics=no");
+                rustc.arg("-Zwrite-long-types-to-disk=no");
                 // FIXME: use this for other modes too, for perf?
                 rustc.arg("-Cstrip=debuginfo");
             }

tests/ui/diagnostic-width/E0271.stderr

@@ -15,8 +15,7 @@ note: expected this to be `Foo`
    |
 LL |     type Error = E;
    |                  ^
-   = note: required for the cast from `Box<Result<..., ...>>` to `Box<(dyn Future<Error = Foo> + 'static)>`
-   = note: the full name for the source type has been written to '$TEST_BUILD_DIR/diagnostic-width/E0271/E0271.long-type-hash.txt'
+   = note: required for the cast from `Box<Result<Result<(), Result<Result<(), Result<Result<(), Option<{integer}>>, ()>>, ()>>, ()>>` to `Box<(dyn Future<Error = Foo> + 'static)>`
 
 error: aborting due to previous error
 

tests/ui/diagnostic-width/long-E0308.rs

@@ -1,4 +1,4 @@
-// compile-flags: --diagnostic-width=60
+// compile-flags: --diagnostic-width=60 -Zwrite-long-types-to-disk=yes
 // normalize-stderr-test: "long-type-\d+" -> "long-type-hash"
 
 mod a {

tests/ui/error-codes/E0271.rs

@@ -1,3 +1,4 @@
+// compile-flags: -Zwrite-long-types-to-disk=yes
 trait Trait { type AssociatedType; }
 
 fn foo<T>(t: T) where T: Trait<AssociatedType=u32> {

tests/ui/error-codes/E0271.stderr

@@ -1,18 +1,18 @@
 error[E0271]: type mismatch resolving `<i8 as Trait>::AssociatedType == u32`
-  --> $DIR/E0271.rs:10:9
+  --> $DIR/E0271.rs:11:9
    |
 LL |     foo(3_i8);
    |     --- ^^^^ type mismatch resolving `<i8 as Trait>::AssociatedType == u32`
    |     |
    |     required by a bound introduced by this call
    |
 note: expected this to be `u32`
-  --> $DIR/E0271.rs:7:43
+  --> $DIR/E0271.rs:8:43
    |
 LL | impl Trait for i8 { type AssociatedType = &'static str; }
    |                                           ^^^^^^^^^^^^
 note: required by a bound in `foo`
-  --> $DIR/E0271.rs:3:32
+  --> $DIR/E0271.rs:4:32
    |
 LL | fn foo<T>(t: T) where T: Trait<AssociatedType=u32> {
    |                                ^^^^^^^^^^^^^^^^^^ required by this bound in `foo`

tests/ui/error-codes/E0275.rs

@@ -1,3 +1,4 @@
+// compile-flags: -Zwrite-long-types-to-disk=yes
 // normalize-stderr-test: "long-type-\d+" -> "long-type-hash"
 trait Foo {}
 

tests/ui/error-codes/E0275.stderr

@@ -1,12 +1,12 @@
 error[E0275]: overflow evaluating the requirement `Bar<Bar<Bar<Bar<Bar<Bar<Bar<...>>>>>>>: Foo`
-  --> $DIR/E0275.rs:6:33
+  --> $DIR/E0275.rs:7:33
    |
 LL | impl<T> Foo for T where Bar<T>: Foo {}
    |                                 ^^^
    |
    = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`E0275`)
 note: required for `Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<Bar<...>>>>>>>>>>>>>>>>>>>>>` to implement `Foo`
-  --> $DIR/E0275.rs:6:9
+  --> $DIR/E0275.rs:7:9
    |
 LL | impl<T> Foo for T where Bar<T>: Foo {}
    |         ^^^     ^               --- unsatisfied trait bound introduced here