Try to remove readavailable sections from REPL precompile (#59179)

The `readavailable` is problematic, because it can read partial error
messages. The `readuntil`s should be safe because they properly fence
between each prompt. If there is some other reason these readavailables
are required, let's find out and replace them with proper readuntils if
we can.

Fixes #59099 (or tries to at least)

Author: Keno

stdlib/REPL/src/precompile.jl

@@ -24,7 +24,8 @@ function repl_workload()
     function check_errors(out)
         str = String(out)
         if occursin("ERROR:", str) && !any(occursin(e, str) for e in allowed_errors)
-            @error "Unexpected error (Review REPL precompilation with debug_output on):\n$str"
+            @error "Unexpected error (Review REPL precompilation with debug_output on):\n$str" exception=(
+                Base.PrecompilableError(), Base.backtrace())
             exit(1)
         end
     end
@@ -40,6 +41,7 @@ function repl_workload()
 
     # This is notified as soon as the first prompt appears
     repl_init_event = Base.Event()
+    repl_init_done_event = Base.Event()
 
     atreplinit() do repl
         # Main is closed so we can't evaluate in it, but atreplinit runs at
@@ -48,6 +50,7 @@ function repl_workload()
         t = @async begin
             wait(repl_init_event)
             REPL.activate(REPL.Precompile; interactive_utils=false)
+            notify(repl_init_done_event)
         end
         Base.errormonitor(t)
     end
@@ -80,6 +83,9 @@ function repl_workload()
     """
 
     JULIA_PROMPT = "julia> "
+    # The help text for `reinterpret` has example `julia>` prompts in it,
+    # so use the longer prompt to avoid desychronization.
+    ACTIVATED_JULIA_PROMPT = "(REPL.Precompile) julia> "
     PKG_PROMPT = "pkg> "
     SHELL_PROMPT = "shell> "
     HELP_PROMPT = "help?> "
@@ -142,18 +148,24 @@ function repl_workload()
             end
             schedule(repltask)
             # wait for the definitive prompt before start writing to the TTY
-            check_errors(readuntil(output_copy, JULIA_PROMPT))
+            check_errors(readuntil(output_copy, JULIA_PROMPT, keep=true))
+
+            # Switch to the activated prompt
+            notify(repl_init_event)
+            wait(repl_init_done_event)
+            write(ptm, "\n")
+            # The prompt prints twice - once for the restatement of the input, once
+            # to indicate ready for the new prompt.
+            check_errors(readuntil(output_copy, ACTIVATED_JULIA_PROMPT, keep=true))
+            check_errors(readuntil(output_copy, ACTIVATED_JULIA_PROMPT, keep=true))
+
             write(debug_output, "\n#### REPL STARTED ####\n")
-            sleep(0.01)
-            check_errors(readavailable(output_copy))
             # Input our script
             precompile_lines = split(repl_script::String, '\n'; keepempty=false)
             curr = 0
             for l in precompile_lines
                 sleep(0.01) # try to let a bit of output accumulate before reading again
                 curr += 1
-                # consume any other output
-                bytesavailable(output_copy) > 0 && check_errors(readavailable(output_copy))
                 # push our input
                 write(debug_output, "\n#### inputting statement: ####\n$(repr(l))\n####\n")
                 # If the line ends with a CTRL_C, don't write an extra newline, which would
@@ -166,13 +178,12 @@ function repl_workload()
                 strbuf = ""
                 while !eof(output_copy)
                     strbuf *= String(readavailable(output_copy))
-                    occursin(JULIA_PROMPT, strbuf) && break
+                    occursin(ACTIVATED_JULIA_PROMPT, strbuf) && break
                     occursin(PKG_PROMPT, strbuf) && break
                     occursin(SHELL_PROMPT, strbuf) && break
                     occursin(HELP_PROMPT, strbuf) && break
                     sleep(0.01) # try to let a bit of output accumulate before reading again
                 end
-                notify(repl_init_event)
                 check_errors(strbuf)
             end
             write(debug_output, "\n#### COMPLETED - Closing REPL ####\n")