Rollup merge of #89082 - smoelius:master, r=kennytm

Implement #85440 (Random test ordering)

This PR adds `--shuffle` and `--shuffle-seed` options to `libtest`. The options are similar to the [`-shuffle` option](https://github.com/golang/go/blob/c894b442d1e5e150ad33fa3ce13dbfab1c037b3a/src/testing/testing.go#L1482-L1499) that was recently added to Go.

Here are the relevant parts of the help message:
```
        --shuffle       Run tests in random order
        --shuffle-seed SEED
                        Run tests in random order; seed the random number
                        generator with SEED
...
By default, the tests are run in alphabetical order. Use --shuffle or set
RUST_TEST_SHUFFLE to run the tests in random order. Pass the generated
"shuffle seed" to --shuffle-seed (or set RUST_TEST_SHUFFLE_SEED) to run the
tests in the same order again. Note that --shuffle and --shuffle-seed do not
affect whether the tests are run in parallel.
```
Is an RFC needed for this?

5 files changed, 28 insertions, 9 deletions

diff --git a/library/test/src/formatters/json.rs b/library/test/src/formatters/json.rs
index 57b6d1a0202..424d3ef7b41 100644
--- a/library/test/src/formatters/json.rs
+++ b/library/test/src/formatters/json.rs
@@ -60,10 +60,15 @@ impl<T: Write> JsonFormatter<T> {
 }
 
 impl<T: Write> OutputFormatter for JsonFormatter<T> {
-    fn write_run_start(&mut self, test_count: usize) -> io::Result<()> {
+    fn write_run_start(&mut self, test_count: usize, shuffle_seed: Option<u64>) -> io::Result<()> {
+        let shuffle_seed_json = if let Some(shuffle_seed) = shuffle_seed {
+            format!(r#", "shuffle_seed": {}"#, shuffle_seed)
+        } else {
+            String::new()
+        };
         self.writeln_message(&*format!(
-            r#"{{ "type": "suite", "event": "started", "test_count": {} }}"#,
-            test_count
+            r#"{{ "type": "suite", "event": "started", "test_count": {}{} }}"#,
+            test_count, shuffle_seed_json
         ))
     }
 
diff --git a/library/test/src/formatters/junit.rs b/library/test/src/formatters/junit.rs
index 04057906d1c..e2aebee916d 100644
--- a/library/test/src/formatters/junit.rs
+++ b/library/test/src/formatters/junit.rs
@@ -27,7 +27,11 @@ impl<T: Write> JunitFormatter<T> {
 }
 
 impl<T: Write> OutputFormatter for JunitFormatter<T> {
-    fn write_run_start(&mut self, _test_count: usize) -> io::Result<()> {
+    fn write_run_start(
+        &mut self,
+        _test_count: usize,
+        _shuffle_seed: Option<u64>,
+    ) -> io::Result<()> {
         // We write xml header on run start
         self.out.write_all(b"\n")?;
         self.write_message("<?xml version=\"1.0\" encoding=\"UTF-8\"?>")
diff --git a/library/test/src/formatters/mod.rs b/library/test/src/formatters/mod.rs
index 2e03581b3af..cb80859759f 100644
--- a/library/test/src/formatters/mod.rs
+++ b/library/test/src/formatters/mod.rs
@@ -18,7 +18,7 @@ pub(crate) use self::pretty::PrettyFormatter;
 pub(crate) use self::terse::TerseFormatter;
 
 pub(crate) trait OutputFormatter {
-    fn write_run_start(&mut self, test_count: usize) -> io::Result<()>;
+    fn write_run_start(&mut self, test_count: usize, shuffle_seed: Option<u64>) -> io::Result<()>;
     fn write_test_start(&mut self, desc: &TestDesc) -> io::Result<()>;
     fn write_timeout(&mut self, desc: &TestDesc) -> io::Result<()>;
     fn write_result(
diff --git a/library/test/src/formatters/pretty.rs b/library/test/src/formatters/pretty.rs
index 9cad71e30bd..4a03b4b9147 100644
--- a/library/test/src/formatters/pretty.rs
+++ b/library/test/src/formatters/pretty.rs
@@ -181,9 +181,14 @@ impl<T: Write> PrettyFormatter<T> {
 }
 
 impl<T: Write> OutputFormatter for PrettyFormatter<T> {
-    fn write_run_start(&mut self, test_count: usize) -> io::Result<()> {
+    fn write_run_start(&mut self, test_count: usize, shuffle_seed: Option<u64>) -> io::Result<()> {
         let noun = if test_count != 1 { "tests" } else { "test" };
-        self.write_plain(&format!("\nrunning {} {}\n", test_count, noun))
+        let shuffle_seed_msg = if let Some(shuffle_seed) = shuffle_seed {
+            format!(" (shuffle seed: {})", shuffle_seed)
+        } else {
+            String::new()
+        };
+        self.write_plain(&format!("\nrunning {} {}{}\n", test_count, noun, shuffle_seed_msg))
     }
 
     fn write_test_start(&mut self, desc: &TestDesc) -> io::Result<()> {
diff --git a/library/test/src/formatters/terse.rs b/library/test/src/formatters/terse.rs
index 0c8215c5dac..1f2c410cd96 100644
--- a/library/test/src/formatters/terse.rs
+++ b/library/test/src/formatters/terse.rs
@@ -170,10 +170,15 @@ impl<T: Write> TerseFormatter<T> {
 }
 
 impl<T: Write> OutputFormatter for TerseFormatter<T> {
-    fn write_run_start(&mut self, test_count: usize) -> io::Result<()> {
+    fn write_run_start(&mut self, test_count: usize, shuffle_seed: Option<u64>) -> io::Result<()> {
         self.total_test_count = test_count;
         let noun = if test_count != 1 { "tests" } else { "test" };
-        self.write_plain(&format!("\nrunning {} {}\n", test_count, noun))
+        let shuffle_seed_msg = if let Some(shuffle_seed) = shuffle_seed {
+            format!(" (shuffle seed: {})", shuffle_seed)
+        } else {
+            String::new()
+        };
+        self.write_plain(&format!("\nrunning {} {}{}\n", test_count, noun, shuffle_seed_msg))
     }
 
     fn write_test_start(&mut self, desc: &TestDesc) -> io::Result<()> {