fix shell borrow state debug asserts

Previously, `gctx.shell().verbosity()` was used to check that `gctx.shell` is
not borrowed. Since shell is now behind a `Mutex` and not a `RefCell`,
this would hang waiting for the unlock instead panicking. Borrow state
checking is now done using `Mutex::try_lock` in
`GlobalContext::debug_assert_shell_not_borrowed`

Author: susitsm

src/cargo/core/registry.rs

@@ -788,11 +788,9 @@ impl<'gctx> Registry for PackageRegistry<'gctx> {
 
     #[tracing::instrument(skip_all)]
     fn block_until_ready(&mut self) -> CargoResult<()> {
-        if cfg!(debug_assertions) {
-            // Force borrow to catch invalid borrows, regardless of which source is used and how it
-            // happens to behave this time
-            self.gctx.shell().verbosity();
-        }
+        // Force borrow to catch invalid borrows, regardless of which source is used and how it
+        // happens to behave this time
+        self.gctx.debug_assert_shell_not_borrowed();
         for (source_id, source) in self.sources.sources_mut() {
             source
                 .block_until_ready()

src/cargo/util/context/mod.rs

@@ -413,6 +413,16 @@ impl GlobalContext {
         self.shell.lock().unwrap()
     }
 
+    /// If debug assertions are enabled, checks that `shell` is not borrowed
+    pub fn debug_assert_shell_not_borrowed(&self) {
+        if cfg!(debug_assertions) {
+            match self.shell.try_lock() {
+                Ok(_) | Err(std::sync::TryLockError::Poisoned(_)) => (),
+                Err(std::sync::TryLockError::WouldBlock) => panic!("shell is borrowed!"),
+            }
+        }
+    }
+
     /// Gets the path to the `rustdoc` executable.
     pub fn rustdoc(&self) -> CargoResult<&Path> {
         self.rustdoc

src/cargo/util/flock.rs

@@ -392,10 +392,8 @@ fn acquire(
     lock_try: &dyn Fn() -> io::Result<()>,
     lock_block: &dyn Fn() -> io::Result<()>,
 ) -> CargoResult<()> {
-    if cfg!(debug_assertions) {
-        // Force borrow to catch invalid borrows outside of contention situations
-        gctx.shell().verbosity();
-    }
+    // Force borrow to catch invalid borrows outside of contention situations
+    gctx.debug_assert_shell_not_borrowed();
     if try_acquire(path, lock_try)? {
         return Ok(());
     }