Fetch miri flags from cargo config

README.md

@@ -110,7 +110,8 @@ their name.
 
 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.
+without checking the aliasing of references. Also, you can set the `miri.flags`
+setting in [cargo configuration](https://doc.rust-lang.org/cargo/reference/config.html).
 
 When compiling code via `cargo miri`, the `cfg(miri)` config flag is set for code
 that will be interpret under Miri. You can use this to ignore test cases that fail
@@ -262,7 +263,22 @@ up the sysroot.  If you are using `miri` (the Miri driver) directly, see the
 [miri-flags]: #miri--z-flags-and-environment-variables
 
 Miri adds its own set of `-Z` flags, which are usually set via the `MIRIFLAGS`
-environment variable. We first document the most relevant and most commonly used flags:
+environment variable or using the `miri.flags` setting in
+[cargo configuration](https://doc.rust-lang.org/cargo/reference/config.html),
+they are mutually exclusive with priority of `MIRIFLAGS` environment variable:
+
+```bash
+MIRIFLAGS="-Zmiri-disable-stacked-borrows" cargo miri run
+```
+
+```toml
+# .cargo/config.toml
+
+[miri]
+flags = ["-Zmiri-disable-isolation", "-Zmiri-report-progress"]
+```
+
+We first document the most relevant and most commonly used flags:
 
 * `-Zmiri-compare-exchange-weak-failure-rate=<rate>` changes the failure rate of
   `compare_exchange_weak` operations. The default is `0.8` (so 4 out of 5 weak ops will fail).

cargo-miri/src/phases.rs

@@ -6,6 +6,7 @@ use std::fs::{self, File};
 use std::io::BufReader;
 use std::path::PathBuf;
 use std::process::Command;
+use std::str;
 
 use crate::{setup::*, util::*};
 
@@ -517,11 +518,10 @@ pub fn phase_runner(mut binary_args: impl Iterator<Item = String>, phase: Runner
             cmd.arg(arg);
         }
     }
-    // Respect `MIRIFLAGS`.
-    if let Ok(a) = env::var("MIRIFLAGS") {
-        // This code is taken from `RUSTFLAGS` handling in cargo.
-        let args = a.split(' ').map(str::trim).filter(|s| !s.is_empty()).map(str::to_string);
-        cmd.args(args);
+
+    // Respect flags.
+    if let Some(flags) = get_miriflags() {
+        cmd.args(flags);
     }
 
     // Then pass binary arguments.
@@ -541,6 +541,27 @@ pub fn phase_runner(mut binary_args: impl Iterator<Item = String>, phase: Runner
     }
 }
 
+fn get_miriflags() -> Option<Vec<String>> {
+    // Fetch miri flags from cargo config.
+    let mut cmd = cargo();
+    cmd.args(["-Zunstable-options", "config", "get", "miri.flags", "--format=json-value"]);
+    let output = cmd.output().expect("failed to run `cargo config`");
+    let config_miriflags =
+        str::from_utf8(&output.stdout).expect("failed to get `cargo config` output");
+
+    // Respect `MIRIFLAGS` and `miri.flags` setting in cargo config.
+    // If MIRIFLAGS is present, flags from cargo config are ignored.
+    // This matches cargo behavior for RUSTFLAGS.
+    if let Ok(a) = env::var("MIRIFLAGS") {
+        // This code is taken from `RUSTFLAGS` handling in cargo.
+        Some(a.split(' ').map(str::trim).filter(|s| !s.is_empty()).map(str::to_string).collect())
+    } else if let Ok(args) = serde_json::from_str::<Vec<String>>(config_miriflags) {
+        Some(args)
+    } else {
+        None
+    }
+}
+
 pub fn phase_rustdoc(mut args: impl Iterator<Item = String>) {
     let verbose = std::env::var("MIRI_VERBOSE")
         .map_or(0, |verbose| verbose.parse().expect("verbosity flag must be an integer"));

test-cargo-miri/run-test.py

@@ -61,7 +61,7 @@ def test(name, cmd, stdout_ref, stderr_ref, stdin=b'', env={}):
 
     stdout_matches = check_output(stdout, stdout_ref, "stdout")
     stderr_matches = check_output(stderr, stderr_ref, "stderr")
-    
+
     if p.returncode == 0 and stdout_matches and stderr_matches:
         # All good!
         return
@@ -90,6 +90,12 @@ def test_no_rebuild(name, cmd, env={}):
         fail("Something was being rebuilt when it should not be (or we got no output)");
 
 def test_cargo_miri_run():
+    # Try to remove cargo config to avoid unexpected settings
+    try:
+        os.remove('.cargo/config.toml')
+    except OSError:
+        pass
+
     test("`cargo miri run` (no isolation)",
         cargo_miri("run"),
         "run.default.stdout.ref", "run.default.stderr.ref",
@@ -99,6 +105,44 @@ def test_cargo_miri_run():
             'MIRITESTVAR': "wrongval", # make sure the build.rs value takes precedence
         },
     )
+
+    # Create a config with isolation disabled
+    try:
+        os.mkdir('.cargo')
+    except OSError:
+        pass
+
+    with open(".cargo/config.toml", "w") as f:
+        f.write('[miri]\nflags = ["-Zmiri-disable-isolation"]')
+
+    # Testing miri.flags are taken in account
+    test("`cargo miri run` (no isolation, set from cargo config)",
+        cargo_miri("run"),
+        "run.default.stdout.ref", "run.default.stderr.ref",
+        stdin=b'12\n21\n',
+        env={
+            'MIRITESTVAR': "wrongval", # make sure the build.rs value takes precedence
+        },
+    )
+
+    # Create an empty config
+    with open(".cargo/config.toml", "w") as f:
+        f.write('[miri]\nflags = [""]')
+
+    # Check that MIRIFLAGS envar has higher precedence tha cargo config
+    test("`cargo miri run` (no isolation, ignoring cargo config)",
+        cargo_miri("run"),
+        "run.default.stdout.ref", "run.default.stderr.ref",
+        stdin=b'12\n21\n',
+        env={
+            'MIRIFLAGS': "-Zmiri-disable-isolation",
+            'MIRITESTVAR': "wrongval", # make sure the build.rs value takes precedence
+        },
+    )
+
+    # Cleaning up config after all config-related tests
+    os.remove('.cargo/config.toml')
+
     # Special test: run it again *without* `-q` to make sure nothing is being rebuilt (Miri issue #1722)
     test_no_rebuild("`cargo miri run` (no rebuild)",
         cargo_miri("run", quiet=False) + ["--", ""],