Rollup merge of #122110 - WaffleLapkin:miri-temp, r=RalfJung

Make `x t miri` respect `MIRI_TEMP`

(I don't want to override `TMPDIR`, as that might affect other things)

r? ``@RalfJung``

Author: GuillaumeGomez

Diff for: src/tools/miri/tests/compiletest.rs

@@ -81,8 +81,10 @@ fn test_config(target: &str, path: &str, mode: Mode, with_dependencies: bool) ->
 
     // Add a test env var to do environment communication tests.
     program.envs.push(("MIRI_ENV_VAR_TEST".into(), Some("0".into())));
+
     // Let the tests know where to store temp files (they might run for a different target, which can make this hard to find).
-    program.envs.push(("MIRI_TEMP".into(), Some(env::temp_dir().into())));
+    let miri_temp = env::var_os("MIRI_TEMP").unwrap_or_else(|| env::temp_dir().into());
+    program.envs.push(("MIRI_TEMP".into(), Some(miri_temp)));
 
     let mut config = Config {
         target: Some(target.to_owned()),

Diff for: src/tools/miri/tests/pass/shims/fs.rs

@@ -1,6 +1,10 @@
 //@ignore-target-windows: File handling is not implemented yet
 //@compile-flags: -Zmiri-disable-isolation
 
+// If this test is failing for you locally, you can try
+// 1. Deleting the files `/tmp/miri_*`
+// 2. Setting `MIRI_TEMP` or `TMPDIR` to a different directory, without the `miri_*` files
+
 #![feature(io_error_more)]
 #![feature(io_error_uncategorized)]