Rollup merge of #112562 - klensy:rd-gui-test-win, r=GuillaumeGomez

rustdoc-gui: allow running on Windows

This adds few fixes to allow running `python x.py test rustdoc-gui` on Windows.

* path to npm required to be `npm.cmd` on Windows (otherwise don't work for me)
* properly parse node module version on Windows
* properly provide path to browser-ui-test runner (fixed in #112613)

r? `@GuillaumeGomez`

Author: matthiaskrgr

config.example.toml

@@ -250,6 +250,13 @@ changelog-seen = 2
 # target when running tests, otherwise this can be omitted.
 #nodejs = "node"
 
+# The npm executable to use. Note that this is used for rustdoc-gui tests,
+# otherwise this can be omitted.
+#
+# Under Windows this should be `npm.cmd` or path to it (verified on nodejs v18.06), or
+# error will be emitted.
+#npm = "npm"
+
 # Python interpreter to use for various tasks throughout the build, notably
 # rustdoc tests, the lldb python interpreter, and some dist bits and pieces.
 #

src/tools/rustdoc-gui-test/src/main.rs

@@ -14,13 +14,19 @@ fn get_browser_ui_test_version_inner(npm: &Path, global: bool) -> Option<String>
     if global {
         command.arg("--global");
     }
-    let lines = command
-        .output()
-        .map(|output| String::from_utf8_lossy(&output.stdout).into_owned())
-        .unwrap_or(String::new());
+    let lines = match command.output() {
+        Ok(output) => String::from_utf8_lossy(&output.stdout).into_owned(),
+        Err(e) => {
+            eprintln!(
+                "path to npm can be wrong, provided path: {npm:?}. Try to set npm path \
+            in config.toml in [build.npm]",
+            );
+            panic!("{:?}", e)
+        }
+    };
     lines
         .lines()
-        .find_map(|l| l.split(':').nth(1)?.strip_prefix("browser-ui-test@"))
+        .find_map(|l| l.rsplit(':').next()?.strip_prefix("browser-ui-test@"))
         .map(|v| v.to_owned())
 }