fix env update, and expand test

Author: RalfJung

src/shims/env.rs

@@ -81,10 +81,10 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         if let Some((name, value)) = new {
             let var_ptr = alloc_env_var_as_c_str(&name, &value, &mut this);
             if let Some(var) = this.machine.env_vars.map.insert(name.to_owned(), var_ptr) {
-                this.update_environ()?;
                 this.memory
                     .deallocate(var, None, MiriMemoryKind::Machine.into())?;
             }
+            this.update_environ()?;
             Ok(0)
         } else {
             Ok(-1)
@@ -100,14 +100,14 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
             let name = this.read_os_str_from_c_str(name_ptr)?.to_owned();
             if !name.is_empty() && !name.to_string_lossy().contains('=') {
                 success = Some(this.machine.env_vars.map.remove(&name));
-                this.update_environ()?;
             }
         }
         if let Some(old) = success {
             if let Some(var) = old {
                 this.memory
                     .deallocate(var, None, MiriMemoryKind::Machine.into())?;
             }
+            this.update_environ()?;
             Ok(0)
         } else {
             Ok(-1)

tests/run-pass/env.rs

@@ -3,11 +3,26 @@
 use std::env;
 
 fn main() {
+    // Test that miri environment is isolated when communication is disabled.
+    // (`MIRI_ENV_VAR_TEST` is set by the test harness.)
+    assert_eq!(env::var("MIRI_ENV_VAR_TEST"), Err(env::VarError::NotPresent));
+
+    // Test base state.
+    println!("{:#?}", env::vars().collect::<Vec<_>>());
     assert_eq!(env::var("MIRI_TEST"), Err(env::VarError::NotPresent));
+
+    // Set the variable.
     env::set_var("MIRI_TEST", "the answer");
     assert_eq!(env::var("MIRI_TEST"), Ok("the answer".to_owned()));
-    // Test that miri environment is isolated when communication is disabled.
-    assert!(env::var("MIRI_ENV_VAR_TEST").is_err());
-    // Test that the new variable is in the `std::env::Vars` iterator
-    assert!(env::vars().any(|(name, value)| name == "MIRI_TEST"))
+    println!("{:#?}", env::vars().collect::<Vec<_>>());
+
+    // Change the variable.
+    env::set_var("MIRI_TEST", "42");
+    assert_eq!(env::var("MIRI_TEST"), Ok("42".to_owned()));
+    println!("{:#?}", env::vars().collect::<Vec<_>>());
+
+    // Remove the variable.
+    env::remove_var("MIRI_TEST");
+    assert_eq!(env::var("MIRI_TEST"), Err(env::VarError::NotPresent));
+    println!("{:#?}", env::vars().collect::<Vec<_>>());
 }

tests/run-pass/env.stdout

@@ -0,0 +1,14 @@
+[]
+[
+    (
+        "MIRI_TEST",
+        "the answer",
+    ),
+]
+[
+    (
+        "MIRI_TEST",
+        "42",
+    ),
+]
+[]