Support test output postprocessing by a child process.

Rationale for adding this functionality:

* Bazel (build system) doesn't provide a way to process output from a
  binary (in this case, Rust test binary's output) other using a wrapper
  binary. However, using a wrapper binary potentially breaks debugging,
  because Bazel would suggest to debug the wrapper binary rather than
  the Rust test itself.
    * See bazelbuild/rules_rust#1303.
    * Cargo is not used in Rust Bazel rules.
    * Although we could wait for
      #96290 and then modify Rust
      Bazel rules to pass `--logfile` on the command line to
      provisionally unblock
      bazelbuild/rules_rust#1303, that
      solution still wouldn't allow advanced test output postprocessing
      such as changing JSON/XML schema and injecting extra JUnit
      properties.
* Due to limitations of Rust libtest formatters, Rust developers often
  use a separate tool to postprocess the test results output (see
  comments to #85563).
    * Examples of existing postprocessing tools:
	* https://crates.io/crates/cargo2junit
	* https://crates.io/crates/gitlab-report
	* https://crates.io/crates/cargo-suity
    * For these use cases, it might be helpful to use the new flags
      `--output_postprocess_executable`, `--output_postprocess_args`
      instead of piping the test output explicitly, e.g. to more
      reliably separate test results from other output.

Rationale for implementation details:

* Use platform-dependent scripts (.sh, .cmd) because it doesn't seem to
  be possible to enable unstable feature `bindeps`
  (https://rust-lang.github.io/rfcs/3028-cargo-binary-dependencies.html)
  in "x.py" by default.
    * Here's a preexisting test that also uses per-platform
      specialization: `library/std/src/process/tests.rs`.

How to use:

```
./testbinary --format=junit -Zunstable-options --output_postprocess_executable=/usr/bin/echo --output_postprocess_args=abc123
```

Cargo.lock

@@ -5445,6 +5445,7 @@ dependencies = [
  "libc",
  "panic_abort",
  "panic_unwind",
+ "rand",
  "std",
 ]
 

library/test/Cargo.toml

@@ -10,3 +10,6 @@ core = { path = "../core" }
 panic_unwind = { path = "../panic_unwind" }
 panic_abort = { path = "../panic_abort" }
 libc = { version = "0.2.150", default-features = false }
+
+[dev-dependencies]
+rand = { version = "0.8.5" }

library/test/src/cli.rs

@@ -31,6 +31,13 @@ pub struct TestOpts {
     /// abort as soon as possible.
     pub fail_fast: bool,
     pub options: Options,
+    /// The test results text output may optionally be piped into the given executable running as
+    /// a child process. The child process inherits the environment variables passed to the test
+    /// binary.
+    ///
+    /// If this is unset, the test results will be written to stdout.
+    pub output_postprocess_executable: Option<PathBuf>,
+    pub output_postprocess_args: Vec<String>,
 }
 
 impl TestOpts {
@@ -148,6 +155,18 @@ fn optgroups() -> getopts::Options {
             "shuffle-seed",
             "Run tests in random order; seed the random number generator with SEED",
             "SEED",
+        )
+        .optopt(
+            "",
+            "output_postprocess_executable",
+            "Postprocess test results using the given executable",
+            "PATH",
+        )
+        .optmulti(
+            "",
+            "output_postprocess_args",
+            "When --output_postprocess_executable is set, pass the given command line arguments to the executable",
+            "ARGUMENT",
         );
     opts
 }
@@ -281,6 +300,9 @@ fn parse_opts_impl(matches: getopts::Matches) -> OptRes {
 
     let options = Options::new().display_output(matches.opt_present("show-output"));
 
+    let output_postprocess_executable = get_output_postprocess_executable(&matches)?;
+    let output_postprocess_args = matches.opt_strs("output_postprocess_args");
+
     let test_opts = TestOpts {
         list,
         filters,
@@ -301,6 +323,8 @@ fn parse_opts_impl(matches: getopts::Matches) -> OptRes {
         time_options,
         options,
         fail_fast: false,
+        output_postprocess_executable,
+        output_postprocess_args,
     };
 
     Ok(test_opts)
@@ -493,3 +517,9 @@ fn get_log_file(matches: &getopts::Matches) -> OptPartRes<Option<PathBuf>> {
 
     Ok(logfile)
 }
+
+fn get_output_postprocess_executable(matches: &getopts::Matches) -> OptPartRes<Option<PathBuf>> {
+    let executable = matches.opt_str("output_postprocess_executable").map(|s| PathBuf::from(&s));
+
+    Ok(executable)
+}

library/test/src/console.rs

@@ -3,6 +3,7 @@
 use std::fs::File;
 use std::io;
 use std::io::prelude::Write;
+use std::process::{Command, Stdio};
 use std::time::Instant;
 
 use super::{
@@ -289,50 +290,89 @@ fn on_test_event(
 }
 
 /// A simple console test runner.
-/// Runs provided tests reporting process and results to the stdout.
+/// Runs provided tests reporting process and results.
+///
+/// The results may optionally be piped to the specified postprocessor binary, otherwise written to stdout.
 pub fn run_tests_console(opts: &TestOpts, tests: Vec<TestDescAndFn>) -> io::Result<bool> {
-    let output = match term::stdout() {
-        None => OutputLocation::Raw(io::stdout()),
-        Some(t) => OutputLocation::Pretty(t),
+    let mut postprocessor = match &opts.output_postprocess_executable {
+        None => None,
+        Some(postprocess_executable) => Some(
+            Command::new(&postprocess_executable)
+                .args(&opts.output_postprocess_args)
+                .stdin(Stdio::piped())
+                .spawn()
+                .expect("failed to execute test output postprocessor"),
+        ),
     };
 
-    let max_name_len = tests
-        .iter()
-        .max_by_key(|t| len_if_padded(t))
-        .map(|t| t.desc.name.as_slice().len())
-        .unwrap_or(0);
+    let write_result;
+    {
+        // This inner block is to make sure `child_stdin` is dropped, so that the pipe
+        // and the postprocessor's stdin is closed to notify it of EOF.
+        //
+        // Otherwise, the postprocessor may be stuck waiting for more input.
+
+        let mut child_stdin;
+        let mut host_stdout;
+        let output = match (&mut postprocessor, term::stdout()) {
+            (Some(child), _) => OutputLocation::Raw({
+                child_stdin = child.stdin.take().unwrap();
+                &mut child_stdin as &mut dyn Write
+            }),
+            (None, None) => OutputLocation::Raw({
+                host_stdout = io::stdout();
+                &mut host_stdout as &mut dyn Write
+            }),
+            (None, Some(t)) => OutputLocation::Pretty(t),
+        };
 
-    let is_multithreaded = opts.test_threads.unwrap_or_else(get_concurrency) > 1;
+        let max_name_len = tests
+            .iter()
+            .max_by_key(|t| len_if_padded(t))
+            .map(|t| t.desc.name.as_slice().len())
+            .unwrap_or(0);
+
+        let is_multithreaded = opts.test_threads.unwrap_or_else(get_concurrency) > 1;
+
+        let mut out: Box<dyn OutputFormatter> = match opts.format {
+            OutputFormat::Pretty => Box::new(PrettyFormatter::new(
+                output,
+                opts.use_color(),
+                max_name_len,
+                is_multithreaded,
+                opts.time_options,
+            )),
+            OutputFormat::Terse => Box::new(TerseFormatter::new(
+                output,
+                opts.use_color(),
+                max_name_len,
+                is_multithreaded,
+            )),
+            OutputFormat::Json => Box::new(JsonFormatter::new(output)),
+            OutputFormat::Junit => Box::new(JunitFormatter::new(output)),
+        };
+        let mut st = ConsoleTestState::new(opts)?;
 
-    let mut out: Box<dyn OutputFormatter> = match opts.format {
-        OutputFormat::Pretty => Box::new(PrettyFormatter::new(
-            output,
-            opts.use_color(),
-            max_name_len,
-            is_multithreaded,
-            opts.time_options,
-        )),
-        OutputFormat::Terse => {
-            Box::new(TerseFormatter::new(output, opts.use_color(), max_name_len, is_multithreaded))
-        }
-        OutputFormat::Json => Box::new(JsonFormatter::new(output)),
-        OutputFormat::Junit => Box::new(JunitFormatter::new(output)),
-    };
-    let mut st = ConsoleTestState::new(opts)?;
+        // Prevent the usage of `Instant` in some cases:
+        // - It's currently not supported for wasm targets.
+        // - We disable it for miri because it's not available when isolation is enabled.
+        let is_instant_supported = !cfg!(target_family = "wasm") && !cfg!(miri);
 
-    // Prevent the usage of `Instant` in some cases:
-    // - It's currently not supported for wasm targets.
-    // - We disable it for miri because it's not available when isolation is enabled.
-    let is_instant_supported =
-        !cfg!(target_family = "wasm") && !cfg!(target_os = "zkvm") && !cfg!(miri);
+        let start_time = is_instant_supported.then(Instant::now);
+        run_tests(opts, tests, |x| on_test_event(&x, &mut st, &mut *out))?;
+        st.exec_time = start_time.map(|t| TestSuiteExecTime(t.elapsed()));
 
-    let start_time = is_instant_supported.then(Instant::now);
-    run_tests(opts, tests, |x| on_test_event(&x, &mut st, &mut *out))?;
-    st.exec_time = start_time.map(|t| TestSuiteExecTime(t.elapsed()));
+        assert!(opts.fail_fast || st.current_test_count() == st.total);
 
-    assert!(opts.fail_fast || st.current_test_count() == st.total);
+        write_result = out.write_run_finish(&st);
+    }
+
+    if let Some(mut child) = postprocessor {
+        let status = child.wait().expect("failed to get test output postprocessor status");
+        assert!(status.success());
+    }
 
-    out.write_run_finish(&st)
+    write_result
 }
 
 // Calculates padding for given test description.

library/test/src/testdata/postprocess.cmd

@@ -0,0 +1,19 @@
+@REM A very basic test output postprocessor. Used in `test_output_postprocessing()`.
+
+@echo off
+
+if [%TEST_POSTPROCESSOR_OUTPUT_FILE%] == [] (
+    echo Required environment variable TEST_POSTPROCESSOR_OUTPUT_FILE is not set.
+    cmd /C exit /B 1
+)
+
+@REM Forward script's input into file.
+find /v "" > %TEST_POSTPROCESSOR_OUTPUT_FILE%
+
+@REM Log every command line argument into the same file.
+:start
+    if [%1] == [] goto done
+    echo %~1>> %TEST_POSTPROCESSOR_OUTPUT_FILE%
+    shift
+    goto start
+:done

library/test/src/testdata/postprocess.sh

@@ -0,0 +1,18 @@
+#!/bin/bash
+#
+# A very basic test output postprocessor. Used in `test_output_postprocessing()`.
+
+if [ -z "$TEST_POSTPROCESSOR_OUTPUT_FILE" ]
+then
+  echo "Required environment variable TEST_POSTPROCESSOR_OUTPUT_FILE is not set."
+  exit 1
+fi
+
+# Forward script's input into file.
+cat /dev/stdin > "$TEST_POSTPROCESSOR_OUTPUT_FILE"
+
+# Log every command line argument into the same file.
+for i in "$@"
+do
+  echo "$i" >> "$TEST_POSTPROCESSOR_OUTPUT_FILE"
+done

library/test/src/tests.rs

@@ -1,3 +1,7 @@
+use rand::RngCore;
+use std::fs;
+use std::path::PathBuf;
+
 use super::*;
 
 use crate::{
@@ -35,10 +39,42 @@ impl TestOpts {
             time_options: None,
             options: Options::new(),
             fail_fast: false,
+            output_postprocess_executable: None,
+            output_postprocess_args: vec![],
+        }
+    }
+}
+
+// These implementations of TempDir and tmpdir are forked from rust/library/std/src/sys_common/io.rs.
+struct TempDir(PathBuf);
+
+impl TempDir {
+    fn join(&self, path: &str) -> PathBuf {
+        let TempDir(ref p) = *self;
+        p.join(path)
+    }
+}
+
+impl Drop for TempDir {
+    fn drop(&mut self) {
+        let TempDir(ref p) = *self;
+        let result = fs::remove_dir_all(p);
+        // Avoid panicking while panicking as this causes the process to
+        // immediately abort, without displaying test results.
+        if !thread::panicking() {
+            result.unwrap();
         }
     }
 }
 
+fn tmpdir() -> TempDir {
+    let p = env::temp_dir();
+    let mut r = rand::thread_rng();
+    let ret = p.join(&format!("rust-{}", r.next_u32()));
+    fs::create_dir(&ret).unwrap();
+    TempDir(ret)
+}
+
 fn one_ignored_one_unignored_test() -> Vec<TestDescAndFn> {
     vec![
         TestDescAndFn {
@@ -478,6 +514,25 @@ fn parse_include_ignored_flag() {
     assert_eq!(opts.run_ignored, RunIgnored::Yes);
 }
 
+#[test]
+fn parse_output_postprocess() {
+    let args = vec![
+        "progname".to_string(),
+        "filter".to_string(),
+        "--output_postprocess_executable".to_string(),
+        "/tmp/postprocess.sh".to_string(),
+        "--output_postprocess_args".to_string(),
+        "--test1=a".to_string(),
+        "--output_postprocess_args=--test2=b".to_string(),
+    ];
+    let opts = parse_opts(&args).unwrap().unwrap();
+    assert_eq!(opts.output_postprocess_executable, Some(PathBuf::from("/tmp/postprocess.sh")));
+    assert_eq!(
+        opts.output_postprocess_args,
+        vec!["--test1=a".to_string(), "--test2=b".to_string()]
+    );
+}
+
 #[test]
 pub fn filter_for_ignored_option() {
     // When we run ignored tests the test filter should filter out all the
@@ -922,3 +977,73 @@ fn test_dyn_bench_returning_err_fails_when_run_as_test() {
     let result = rx.recv().unwrap().result;
     assert_eq!(result, TrFailed);
 }
+
+#[test]
+fn test_output_postprocessing() {
+    let desc = TestDescAndFn {
+        desc: TestDesc {
+            name: StaticTestName("whatever"),
+            ignore: false,
+            ignore_message: None,
+            source_file: "",
+            start_line: 0,
+            start_col: 0,
+            end_line: 0,
+            end_col: 0,
+            should_panic: ShouldPanic::No,
+            compile_fail: false,
+            no_run: false,
+            test_type: TestType::Unknown,
+        },
+        testfn: DynTestFn(Box::new(move || Ok(()))),
+    };
+
+    let mut test_postprocessor: PathBuf = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
+    if cfg!(target_os = "windows") {
+        test_postprocessor.push("src/testdata/postprocess.cmd");
+    } else {
+        test_postprocessor.push("src/testdata/postprocess.sh");
+    }
+
+    let tmpdir = tmpdir();
+    let output_path = &tmpdir.join("output.txt");
+
+    std::env::set_var("TEST_POSTPROCESSOR_OUTPUT_FILE", output_path);
+
+    let opts = TestOpts {
+        run_tests: true,
+        output_postprocess_executable: Some(test_postprocessor),
+        output_postprocess_args: vec!["--test1=a".to_string(), "--test2=b".to_string()],
+        format: OutputFormat::Json,
+        ..TestOpts::new()
+    };
+    run_tests_console(&opts, vec![desc]).unwrap();
+
+    // Read output and replace the decimal value at `"exec_time": 0.000084974` to make the text deterministic.
+    // This replacement could be done easier with a regex, but `std` has no regex.
+    let mut contents =
+        fs::read_to_string(output_path).expect("Test postprocessor did not create file");
+    let replace_trigger = r#""exec_time": "#;
+    let replace_start =
+        contents.find(replace_trigger).expect("exec_time not found in the output JSON")
+            + replace_trigger.len();
+    let replace_end = replace_start
+        + contents[replace_start..]
+            .find(' ')
+            .expect("No space found after the decimal value for exec_time");
+    contents.replace_range(replace_start..replace_end, "AAA.BBB");
+
+    // Split output at line breaks to make the comparison platform-agnostic regarding newline style.
+    let contents_lines = contents.as_str().lines().collect::<Vec<&str>>();
+
+    let expected_lines = vec![
+        r#"{ "type": "suite", "event": "started", "test_count": 1 }"#,
+        r#"{ "type": "test", "event": "started", "name": "whatever" }"#,
+        r#"{ "type": "test", "name": "whatever", "event": "ok" }"#,
+        r#"{ "type": "suite", "event": "ok", "passed": 1, "failed": 0, "ignored": 0, "measured": 0, "filtered_out": 0, "exec_time": AAA.BBB }"#,
+        r#"--test1=a"#,
+        r#"--test2=b"#,
+    ];
+
+    assert_eq!(contents_lines, expected_lines);
+}