Auto merge of #141210 - RalfJung:miri-std-doctests, r=<try>

tools-aux ci runner: also cross-test doctests in Miri

Miri now supports running doctests across different targets. Let's use that to run the std doctests on aarch64-apple-darwin, i686-pc-windows-msvc.

try-job: x86_64-gnu-aux

Author: bors

library/std/src/io/mod.rs

@@ -2335,6 +2335,7 @@ pub trait BufRead: Read {
     /// #![feature(buf_read_has_data_left)]
     /// use std::io;
     /// use std::io::prelude::*;
+    /// # if cfg!(all(miri, windows)) { return; } // FIXME(miri-windows-file-access)
     ///
     /// let stdin = io::stdin();
     /// let mut stdin = stdin.lock();

src/bootstrap/mk/Makefile.in

@@ -60,7 +60,8 @@ check-aux:
 		library/alloc \
 		$(BOOTSTRAP_ARGS) \
 		--no-doc
-	# Some doctests use file system operations to demonstrate dealing with `Result`.
+	# Some doctests use file system operations to demonstrate dealing with `Result`,
+	# so we have to run them with isolation disabled.
 	$(Q)MIRIFLAGS="-Zmiri-disable-isolation" \
 		$(BOOTSTRAP) miri --stage 2 \
 		library/coretests \
@@ -72,20 +73,13 @@ check-aux:
 	$(Q)MIRIFLAGS="-Zmiri-disable-isolation" \
 		$(BOOTSTRAP) miri --stage 2 library/std \
 		$(BOOTSTRAP_ARGS) \
-		--no-doc -- \
-		--skip fs:: --skip net:: --skip process:: --skip sys::fd:: --skip sys::pal::
-	$(Q)MIRIFLAGS="-Zmiri-disable-isolation" \
-		$(BOOTSTRAP) miri --stage 2 library/std \
-		$(BOOTSTRAP_ARGS) \
-		--doc -- \
 		--skip fs:: --skip net:: --skip process:: --skip sys::fd:: --skip sys::pal::
 	# Also test some very target-specific modules on other targets
 	# (making sure to cover an i686 target as well).
 	$(Q)MIRIFLAGS="-Zmiri-disable-isolation" BOOTSTRAP_SKIP_TARGET_SANITY=1 \
 		$(BOOTSTRAP) miri --stage 2 library/std \
 		$(BOOTSTRAP_ARGS) \
 		--target aarch64-apple-darwin,i686-pc-windows-msvc \
-		--no-doc -- \
 		time:: sync:: thread:: env::
 dist:
 	$(Q)$(BOOTSTRAP) dist $(BOOTSTRAP_ARGS)