update docs, and also use MIRIFLAGS for the test suite

Author: RalfJung

README.md

@@ -83,11 +83,10 @@ Now you can run your project in Miri:
 The first time you run Miri, it will perform some extra setup and install some
 dependencies.  It will ask you for confirmation before installing anything.
 
-You can pass arguments to Miri after the first `--`, and pass arguments to the
-interpreted program or test suite after the second `--`.  For example, `cargo
-miri run -- -Zmiri-disable-stacked-borrows` runs the program without checking
-the aliasing of references.  To filter the tests being run, use `cargo miri test
--- -- filter`.
+`cargo miri run/test` supports the exact same flags as `cargo run/test`.  You
+can pass arguments to Miri via `MIRIFLAGS`. For example,
+`MIRIFLAGS="-Zmiri-disable-stacked-borrows" cargo miri run` runs the program
+without checking the aliasing of references.
 
 Miri supports cross-execution: if you want to run the program as if it was a
 Linux program, you can do `cargo miri run --target x86_64-unknown-linux-gnu`.
@@ -163,7 +162,8 @@ up the sysroot.  If you are using `miri` (the Miri driver) directly, see the
 ## Miri `-Z` flags and environment variables
 [miri-flags]: #miri--z-flags-and-environment-variables
 
-Miri adds its own set of `-Z` flags:
+Miri adds its own set of `-Z` flags, which are usually set via the `MIRIFLAGS`
+environment variable:
 
 * `-Zmiri-disable-alignment-check` disables checking pointer alignment, so you
   can focus on other failures, but it means Miri can miss bugs in your program.
@@ -229,14 +229,14 @@ Moreover, Miri recognizes some environment variables:
 
 * `MIRI_LOG`, `MIRI_BACKTRACE` control logging and backtrace printing during
   Miri executions, also [see above][testing-miri].
+* `MIRIFLAGS` (recognized by `cargo miri` and the test suite) defines extra
+  flags to be passed to Miri.
 * `MIRI_SYSROOT` (recognized by `cargo miri` and the test suite)
   indicates the sysroot to use.  To do the same thing with `miri`
   directly, use the `--sysroot` flag.
 * `MIRI_TEST_TARGET` (recognized by the test suite) indicates which target
   architecture to test against.  `miri` and `cargo miri` accept the `--target`
   flag for the same purpose.
-* `MIRI_TEST_FLAGS` (recognized by the test suite) defines extra flags to be
-  passed to Miri.
 
 The following environment variables are internal, but used to communicate between
 different Miri binaries, and as such worth documenting:

ci.sh

@@ -26,7 +26,7 @@ function run_tests {
   if ! [ -n "${MIRI_TEST_TARGET+exists}" ]; then
     # Only for host architecture: tests with MIR optimizations
     # FIXME: only testing level 2 because of <https://github.com/rust-lang/rust/issues/76432>.
-    MIRI_TEST_FLAGS="-Z mir-opt-level=2" ./miri test --locked
+    MIRIFLAGS="-Z mir-opt-level=2" ./miri test --locked
   fi
   # "miri test" has built the sysroot for us, now this should pass without
   # any interactive questions.

tests/compiletest.rs

@@ -27,7 +27,7 @@ fn run_tests(mode: &str, path: &str, target: &str) {
     if let Ok(sysroot) = std::env::var("MIRI_SYSROOT") {
         flags.push(format!("--sysroot {}", sysroot));
     }
-    if let Ok(extra_flags) = std::env::var("MIRI_TEST_FLAGS") {
+    if let Ok(extra_flags) = std::env::var("MIRIFLAGS") {
         flags.push(extra_flags);
     }