fix: avoid stopping machine running current dir ops in isolation

get and set current dir operations used to halt the machine by
throwing an exception in isolation mode. This change updates them to
return a dummy NotFound error instead, and keep the machine running.

I started with a custom error using `ErrorKind::Other`, but since it
can't be mapped to a raw OS error, I dropped it. NotFound kind of make
sense for get operations, but not much for set operations. But that's
the only error supported for windows currently.

src/shims/env.rs

@@ -1,6 +1,7 @@
 use std::convert::TryFrom;
 use std::env;
 use std::ffi::{OsStr, OsString};
+use std::io::{Error, ErrorKind};
 
 use rustc_data_structures::fx::FxHashMap;
 use rustc_mir::interpret::Pointer;
@@ -321,20 +322,24 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
             "`getcwd` is only available for the UNIX target family"
         );
 
-        this.check_no_isolation("`getcwd`")?;
-
-        let buf = this.read_scalar(&buf_op)?.check_init()?;
-        let size = this.read_scalar(&size_op)?.to_machine_usize(&*this.tcx)?;
-        // If we cannot get the current directory, we return null
-        match env::current_dir() {
-            Ok(cwd) => {
-                if this.write_path_to_c_str(&cwd, buf, size)?.0 {
-                    return Ok(buf);
+        if this.machine.communicate {
+            let buf = this.read_scalar(&buf_op)?.check_init()?;
+            let size = this.read_scalar(&size_op)?.to_machine_usize(&*this.tcx)?;
+            // If we cannot get the current directory, we return null
+            match env::current_dir() {
+                Ok(cwd) => {
+                    if this.write_path_to_c_str(&cwd, buf, size)?.0 {
+                        return Ok(buf);
+                    }
+                    let erange = this.eval_libc("ERANGE")?;
+                    this.set_last_error(erange)?;
                 }
-                let erange = this.eval_libc("ERANGE")?;
-                this.set_last_error(erange)?;
+                Err(e) => this.set_last_error_from_io_error(e)?,
             }
-            Err(e) => this.set_last_error_from_io_error(e)?,
+        } else {
+            // Emulate an error in isolation mode
+            let err = Error::new(ErrorKind::NotFound, "`getcwd` not available in isolation mode");
+            this.set_last_error_from_io_error(err)?;
         }
         Ok(Scalar::null_ptr(&*this.tcx))
     }
@@ -348,16 +353,20 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         let this = self.eval_context_mut();
         this.assert_target_os("windows", "GetCurrentDirectoryW");
 
-        this.check_no_isolation("`GetCurrentDirectoryW`")?;
+        if this.machine.communicate {
+            let size = u64::from(this.read_scalar(size_op)?.to_u32()?);
+            let buf = this.read_scalar(buf_op)?.check_init()?;
 
-        let size = u64::from(this.read_scalar(size_op)?.to_u32()?);
-        let buf = this.read_scalar(buf_op)?.check_init()?;
-
-        // If we cannot get the current directory, we return 0
-        match env::current_dir() {
-            Ok(cwd) =>
-                return Ok(windows_check_buffer_size(this.write_path_to_wide_str(&cwd, buf, size)?)),
-            Err(e) => this.set_last_error_from_io_error(e)?,
+            // If we cannot get the current directory, we return 0
+            match env::current_dir() {
+                Ok(cwd) =>
+                    return Ok(windows_check_buffer_size(this.write_path_to_wide_str(&cwd, buf, size)?)),
+                Err(e) => this.set_last_error_from_io_error(e)?,
+            }
+        } else {
+            // Emulate an error in isolation mode
+            let err = Error::new(ErrorKind::NotFound, "`GetCurrentDirectoryW` not available in isolation mode");
+            this.set_last_error_from_io_error(err)?;
         }
         Ok(0)
     }
@@ -370,16 +379,21 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
             "`getcwd` is only available for the UNIX target family"
         );
 
-        this.check_no_isolation("`chdir`")?;
-
-        let path = this.read_path_from_c_str(this.read_scalar(path_op)?.check_init()?)?;
+        if this.machine.communicate {
+            let path = this.read_path_from_c_str(this.read_scalar(path_op)?.check_init()?)?;
 
-        match env::set_current_dir(path) {
-            Ok(()) => Ok(0),
-            Err(e) => {
-                this.set_last_error_from_io_error(e)?;
-                Ok(-1)
+            match env::set_current_dir(path) {
+                Ok(()) => Ok(0),
+                Err(e) => {
+                    this.set_last_error_from_io_error(e)?;
+                    Ok(-1)
+                }
             }
+        } else {
+            // Emulate an error in isolation mode
+            let err = Error::new(ErrorKind::NotFound, "`chdir` not available in isolation mode");
+            this.set_last_error_from_io_error(err)?;
+            Ok(-1)
         }
     }
 
@@ -393,16 +407,21 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         let this = self.eval_context_mut();
         this.assert_target_os("windows", "SetCurrentDirectoryW");
 
-        this.check_no_isolation("`SetCurrentDirectoryW`")?;
-
-        let path = this.read_path_from_wide_str(this.read_scalar(path_op)?.check_init()?)?;
+        if this.machine.communicate {
+            let path = this.read_path_from_wide_str(this.read_scalar(path_op)?.check_init()?)?;
 
-        match env::set_current_dir(path) {
-            Ok(()) => Ok(1),
-            Err(e) => {
-                this.set_last_error_from_io_error(e)?;
-                Ok(0)
+            match env::set_current_dir(path) {
+                Ok(()) => Ok(1),
+                Err(e) => {
+                    this.set_last_error_from_io_error(e)?;
+                    Ok(0)
+                }
             }
+        } else {
+            // Emulate an error in isolation mode
+            let err = Error::new(ErrorKind::NotFound, "`SetCurrentDirectoryW` not available in isolation mode");
+            this.set_last_error_from_io_error(err)?;
+            Ok(0)
         }
     }
 

tests/run-pass/current_dir_with_isolation.rs

@@ -0,0 +1,9 @@
+use std::env;
+use std::io::ErrorKind;
+
+fn main() {
+    // Test that current dir operations return the dummy error instead
+    // of stopping the machine in isolation mode
+    assert_eq!(env::current_dir().unwrap_err().kind(), ErrorKind::NotFound);
+    assert_eq!(env::set_current_dir("..").unwrap_err().kind(), ErrorKind::NotFound);
+}