fix: Watch command should not spawn more than one tsc watch (#5391)

The watch command was spawning multiple tsc watch processes, which
conflicted with each other. This could happen if a generate was kicked
off while another one was running, which is now prevented via a
lockfile; if a generate tries to run while the lock is set, it just
sleeps for a few seconds and retries later.

The other issue is that the tsc watch was not getting killed by the
`stop_tsc_watch` function. It seems that yarn starts whatever command it
receives as a detached process, so killing the parent still left a
zombie tsc watch running. By calling tsc directly we now start the
process ourselves and get the proper pid to kill it later.

Please read [contributing guidelines](CONTRIBUTING.md) and remove this
line.

yarn-project/watch.sh

@@ -1,5 +1,5 @@
 #!/usr/bin/env bash
-set -eu
+set -u
 
 DEBOUNCE_DURATION=3 # Set a high duration for debounce since nargo build may pause for a long time during a compilation
 INOTIFY_EVENTS="modify,create,delete,move"
@@ -23,33 +23,52 @@ debounce() {
 
 # Start typescript watch process in the background and store process ID in a file
 start_tsc_watch() {
-  yarn tsc -b tsconfig.json --watch &
+  local tsc_bin=$(yarn bin tsc)
+  $tsc_bin -b tsconfig.json --watch &
   TSC_PID=$!
   echo "$TSC_PID" > .tsc.pid
 }
 
 # Stops the typescript watch process
 stop_tsc_watch() {
-  local tsc_pid=$(cat ".tsc.pid");
-  kill $tsc_pid || true
+  if [ -f .tsc.pid ]; then
+    echo "Stopping tsc watch..."
+    local tsc_pid=$(cat ".tsc.pid");
+    echo KILLING $tsc_pid
+    kill $tsc_pid
+  fi
 }
 
 # Kill typescript, run a yarn generate, and restart typescript
 run_generate() {
-  echo "Change detected at $1"
+  # If already generating something, then try again in a few seconds
+  if [ -f .generating.lock ]; then
+    debounce run_generate $1
+    return
+  fi
+  # Pause ts watch to generate code and acquire a lock
+  echo "LOCKED" > .generating.lock
+  echo "Change detected at $1..."
   stop_tsc_watch
-  FORCE_COLOR=true yarn workspaces foreach --parallel --topological-dev --verbose run generate:$1
-  echo "Generate complete, restarting typescript..."
+  if FORCE_COLOR=true yarn workspaces foreach --parallel --topological-dev --verbose run generate:$1; then
+    echo "Generate complete, restarting tsc watch..."
+  else
+    echo "Generate failed, restarting tsc watch..."
+  fi
+  # Restart tsc watch and release lock
   sleep 3
   start_tsc_watch
+  rm .generating.lock
 }
 
 # Remove all temp files with process or run ids on exit
 cleanup() {
-  rm .tsc.pid || true
-  rm .debounce-* || true
+  rm -f .tsc.pid || true
+  rm -f .debounce-* || true
+  rm -f .generating.lock || true
 }
 trap cleanup EXIT
+cleanup
 
 # Start tsc watch in background
 start_tsc_watch
@@ -68,7 +87,7 @@ while true; do
         debounce run_generate "l1-contracts"
         ;;
       *)
-        echo "Change at $folder not matched with any project"
+        echo "Error: change at $folder not matched with any project"
         exit 1
         ;;
     esac