rustdoc: Test --format=junit

Copied validate_junit.py from libtest-junit.

JUnit format works well in edition 2021, but is currently broken
in edition 2024 by the mergeable doctest report.

tests/run-make/doctests-junit/doctest-2021.xml

@@ -0,0 +1 @@
+<?xml version="1.0" encoding="UTF-8"?><testsuites><testsuite name="test" package="test" id="0" errors="0" failures="0" tests="3" skipped="0" ><testcase classname="doctest.rs" name="add (line 1)" time="$TIME"/><testcase classname="doctest.rs" name="add (line 5)" time="$TIME"/><testcase classname="doctest.rs" name="add (line 9)" time="$TIME"/><system-out/><system-err/></testsuite></testsuites>

tests/run-make/doctests-junit/doctest.rs

@@ -0,0 +1,14 @@
+/// ```
+/// assert_eq!(doctest::add(2, 2), 4);
+/// ```
+///
+/// ```should_panic
+/// assert_eq!(doctest::add(2, 2), 5);
+/// ```
+///
+/// ```compile_fail
+/// assert_eq!(doctest::add(2, 2), "banana");
+/// ```
+pub fn add(a: i32, b: i32) -> i32 {
+    a + b
+}

tests/run-make/doctests-junit/rmake.rs

@@ -0,0 +1,72 @@
+// Check rustdoc's test JUnit (XML) output against snapshots.
+
+//@ ignore-cross-compile (running doctests)
+//@ needs-unwind (test file contains `should_panic` test)
+
+use std::path::Path;
+
+use run_make_support::{cwd, diff, python_command, rustc, rustdoc};
+
+fn main() {
+    let rlib = cwd().join("libdoctest.rlib");
+    rustc().input("doctest.rs").crate_type("rlib").output(&rlib).run();
+
+    run_doctests(&rlib, "2021", "doctest-2021.xml");
+    run_doctests_fail(&rlib, "2024");
+}
+
+#[track_caller]
+fn run_doctests(rlib: &Path, edition: &str, expected_xml: &str) {
+    let rustdoc_out = rustdoc()
+        .input("doctest.rs")
+        .args(&[
+            "--test",
+            "--test-args=-Zunstable-options",
+            "--test-args=--test-threads=1",
+            "--test-args=--format=junit",
+        ])
+        .edition(edition)
+        .env("RUST_BACKTRACE", "0")
+        .extern_("doctest", rlib.display().to_string())
+        .run();
+    let rustdoc_stdout = &rustdoc_out.stdout_utf8();
+
+    python_command().arg("validate_junit.py").stdin_buf(rustdoc_stdout).run();
+
+    diff()
+        .expected_file(expected_xml)
+        .actual_text("output", rustdoc_stdout)
+        .normalize(r#"\btime="[0-9.]+""#, r#"time="$$TIME""#)
+        .run();
+}
+
+// FIXME: gone in the next patch
+#[track_caller]
+fn run_doctests_fail(rlib: &Path, edition: &str) {
+    let rustdoc_out = rustdoc()
+        .input("doctest.rs")
+        .args(&[
+            "--test",
+            "--test-args=-Zunstable-options",
+            "--test-args=--test-threads=1",
+            "--test-args=--format=junit",
+        ])
+        .edition(edition)
+        .env("RUST_BACKTRACE", "0")
+        .extern_("doctest", rlib.display().to_string())
+        .run_fail();
+    let rustdoc_stderr = &rustdoc_out.stderr_utf8();
+
+    diff()
+        .expected_text(
+            "expected",
+            r#"
+thread 'main' ($TID) panicked at library/test/src/formatters/junit.rs:22:9:
+assertion failed: !s.contains('\n')
+note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+"#,
+        )
+        .actual_text("actual", rustdoc_stderr)
+        .normalize(r#"thread 'main' \([0-9]+\)"#, r#"thread 'main' ($$TID)"#)
+        .run();
+}

tests/run-make/doctests-junit/validate_junit.py

@@ -0,0 +1,22 @@
+#!/usr/bin/env python
+
+# Trivial Python script that reads lines from stdin, and checks that each line
+# is a well-formed XML document.
+#
+# This takes advantage of the fact that Python has a built-in XML parser,
+# whereas doing the same check in Rust would require us to pull in an XML
+# crate just for this relatively-minor test.
+#
+# If you're trying to remove Python scripts from the test suite, think twice
+# before removing this one. You could do so, but it's probably not worth it.
+
+import sys
+import xml.etree.ElementTree as ET
+
+# Read the entire output and try to decode it as XML.
+junit = sys.stdin.read()
+try:
+    ET.fromstring(junit)
+except ET.ParseError:
+    print("Invalid xml: %r" % junit)
+    raise