Rollup merge of #100206 - RalfJung:miri-terminfo, r=thomcc

test: skip terminfo parsing in Miri

Terminfo parsing takes a significant amount of time in Miri, making libtest startup very slow. To work around that Miri in fact unsets the `TERM` variable. However, this means we don't get colors in `cargo miri test`.

So I propose we add some logic in libtest that skips parsing terminfo files under Miri, and just uses the regular basic coloring commands (taken from the `colored` crate).

As far as I can see, these two commands are all that libtest ever needs from terminfo, so Miri doesn't even lose any functionality through this. If you want I can entirely remove the terminfo parsing code and just use these commands instead.

Cc https://github.com/rust-lang/miri/issues/2292 `@saethlin`

library/test/src/term/terminfo/mod.rs

@@ -80,6 +80,17 @@ impl TermInfo {
 
     /// Creates a TermInfo for the named terminal.
     pub(crate) fn from_name(name: &str) -> Result<TermInfo, Error> {
+        if cfg!(miri) {
+            // Avoid all the work of parsing the terminfo (it's pretty slow under Miri), and just
+            // assume that the standard color codes work (like e.g. the 'colored' crate).
+            return Ok(TermInfo {
+                names: Default::default(),
+                bools: Default::default(),
+                numbers: Default::default(),
+                strings: Default::default(),
+            });
+        }
+
         get_dbpath_for_term(name)
             .ok_or_else(|| {
                 Error::IoError(io::Error::new(io::ErrorKind::NotFound, "terminfo file not found"))
@@ -119,6 +130,12 @@ pub(crate) struct TerminfoTerminal<T> {
 impl<T: Write + Send> Terminal for TerminfoTerminal<T> {
     fn fg(&mut self, color: color::Color) -> io::Result<bool> {
         let color = self.dim_if_necessary(color);
+        if cfg!(miri) && color < 8 {
+            // The Miri logic for this only works for the most basic 8 colors, which we just assume
+            // the terminal will support. (`num_colors` is always 0 in Miri, so higher colors will
+            // just fail. But libtest doesn't use any higher colors anyway.)
+            return write!(self.out, "\x1B[3{color}m").and(Ok(true));
+        }
         if self.num_colors > color {
             return self.apply_cap("setaf", &[Param::Number(color as i32)]);
         }
@@ -126,6 +143,9 @@ impl<T: Write + Send> Terminal for TerminfoTerminal<T> {
     }
 
     fn reset(&mut self) -> io::Result<bool> {
+        if cfg!(miri) {
+            return write!(self.out, "\x1B[0m").and(Ok(true));
+        }
         // are there any terminals that have color/attrs and not sgr0?
         // Try falling back to sgr, then op
         let cmd = match ["sgr0", "sgr", "op"].iter().find_map(|cap| self.ti.strings.get(*cap)) {