Rename FISH_TSAN_WORKAROUNDS and add feature to Cargo.toml

rustc 1.80 now complains about features not declared in Cargo.toml and cfg
keys/values not declared by build.rs to protect against typos or misuse (you
think you're using the right condition but you're not). See
rust-lang/cargo#10554 and rust-lang/rust#82450.

(We're not actually using TSAN under CI at this time, but I do want to re-enable
it at some point — especially if we get multithreaded execution going — using
the rust-native TSAN configuration.)

I'll be updating the `rsconf` crate and patching `build.rs` accordingly to also
handle the warnings about unknown cfg values, but tsan is a feature and not a
cfg and these can be dealt with in `Cargo.toml` directly.

Cargo.toml

@@ -69,6 +69,7 @@ benchmark = []
 
 # The following features are auto-detected by the build-script and should not be enabled manually.
 asan = []
+tsan = []
 
 [lints]
 rust.non_camel_case_types = "allow"

src/parse_constants.rs

@@ -442,9 +442,9 @@ pub const FISH_MAX_STACK_DEPTH: usize = 128;
 
 /// Maximum number of nested string substitutions (in lieu of evals)
 /// Reduced under TSAN: our CI test creates 500 jobs and this is very slow with TSAN.
-#[cfg(feature = "FISH_TSAN_WORKAROUNDS")]
+#[cfg(feature = "tsan")]
 pub const FISH_MAX_EVAL_DEPTH: usize = 250;
-#[cfg(not(feature = "FISH_TSAN_WORKAROUNDS"))]
+#[cfg(not(feature = "tsan"))]
 pub const FISH_MAX_EVAL_DEPTH: usize = 500;
 
 /// Error message on a function that calls itself immediately.

src/signal.rs

@@ -230,7 +230,7 @@ pub fn signal_set_handlers(interactive: bool) {
         set_interactive_handlers();
     }
 
-    if cfg!(feature = "FISH_TSAN_WORKAROUNDS") {
+    if cfg!(feature = "tsan") {
         // Work around the following TSAN bug:
         // The structure containing signal information for a thread is lazily allocated by TSAN.
         // It is possible for the same thread to receive two allocations, if the signal handler

src/topic_monitor.rs

@@ -187,7 +187,7 @@ impl binary_semaphore_t {
         // a signal call, so if we're blocked in read() (like the topic monitor wants to be!),
         // we'll never receive SIGCHLD and so deadlock. So if tsan is enabled, we mark our fd as
         // non-blocking (so reads will never block) and use select() to poll it.
-        if cfg!(feature = "FISH_TSAN_WORKAROUNDS") {
+        if cfg!(feature = "tsan") {
             let _ = make_fd_nonblocking(pipes.read.as_raw_fd());
         }
 
@@ -239,7 +239,7 @@ impl binary_semaphore_t {
                     // Under tsan our notifying pipe is non-blocking, so we would busy-loop on the read()
                     // call until data is available (that is, fish would use 100% cpu while waiting for
                     // processes). This call prevents that.
-                    if cfg!(feature = "FISH_TSAN_WORKAROUNDS") {
+                    if cfg!(feature = "tsan") {
                         let _ =
                             fd_readable_set_t::is_fd_readable(fd, fd_readable_set_t::kNoTimeout);
                     }