Make the interface to be compatible with GCL-compiled fricas package

src/sage/features/fricas.py

@@ -67,9 +67,12 @@ def is_functional(self):
             sage: FriCAS().is_functional()  # optional - fricas
             FeatureTestResult('fricas', True)
         """
-        command = ['fricas -nosman -eval ")quit"']
+        # Use stdin to pass the quit command instead of -eval because
+        # GCL-compiled FriCAS misinterprets -eval ")quit" as a Lisp expression.
+        # See :issue:`40569`.
+        command = ['fricas', '-nosman']
         try:
-            lines = subprocess.check_output(command, stderr=subprocess.STDOUT, shell=True)
+            lines = subprocess.check_output(command, input=b')quit\n', stderr=subprocess.STDOUT, shell=False)
         except subprocess.CalledProcessError as e:
             return FeatureTestResult(self, False,
                                      reason="Call `{command}` failed with exit code {e.returncode}".format(command=" ".join(command), e=e))

src/sage/interfaces/fricas.py

@@ -197,6 +197,7 @@
 
 import re
 import os
+import pexpect
 
 import sage.interfaces.abc
 
@@ -315,6 +316,7 @@ def __init__(self, name='fricas', command=None,
         assert max(len(c) for c in FRICAS_INIT_CODE) < eval_using_file_cutoff
         self.__eval_using_file_cutoff = eval_using_file_cutoff
         self._COMMANDS_CACHE = '%s/%s_commandlist_cache.sobj' % (DOT_SAGE, name)
+        self._uses_gcl = None  # will be set in _start()
         # we run the init code in _start to avoid spurious output
         Expect.__init__(self,
                         name=name,
@@ -353,6 +355,28 @@ def _start(self):
         self.eval(FRICAS_LINENUMBER_OFF_CODE, reformat=False)
         for line in FRICAS_HELPER_CODE:
             self.eval(line, reformat=False)
+        # Detect whether FriCAS is compiled with GCL.
+        # GCL-based FriCAS may output function declaration messages
+        # asynchronously after the prompt appears. We need to handle this
+        # to keep the expect interface synchronized. See :issue:`40569`.
+        E = self._expect
+        # First, consume any buffered output from previous commands
+        # to ensure we get a clean response to the lisp command
+        while True:
+            try:
+                E.expect(self._prompt, timeout=0.1)
+            except pexpect.TIMEOUT:
+                break
+        E.sendline(')lisp (lisp-implementation-type)')
+        E.expect(self._prompt)
+        lisp_output = E.before.decode() if isinstance(E.before, bytes) else E.before
+        self._uses_gcl = 'GCL' in lisp_output
+        if self._uses_gcl:
+            for _ in range(3):
+                try:
+                    E.expect(self._prompt, timeout=0.1)
+                except pexpect.TIMEOUT:
+                    break
         # register translations between SymbolicRing and FriCAS Expression
         self._register_symbols()
 
@@ -896,6 +920,34 @@ def _repr_(self):
         """
         return "FriCAS"
 
+    def _eval_line(self, line, allow_use_file=True, wait_for_prompt=True, restart_if_needed=True):
+        """
+        Evaluate a single line of code.
+
+        This method overrides :meth:`sage.interfaces.expect.Expect._eval_line`
+        to handle FriCAS compiled with GCL, which may output a double prompt
+        after each command due to buffering issues.
+
+        See :issue:`40569`.
+
+        TESTS::
+
+            sage: fricas(1+1)  # indirect doctest
+            2
+        """
+        result = Expect._eval_line(self, line, allow_use_file=allow_use_file,
+                                   wait_for_prompt=wait_for_prompt,
+                                   restart_if_needed=restart_if_needed)
+        # FriCAS compiled with GCL may send an extra prompt after each command.
+        # We try to consume it to keep the interface synchronized.
+        # Only do this for GCL-based FriCAS to avoid slowdowns with SBCL.
+        if self._uses_gcl and wait_for_prompt and self._expect is not None:
+            try:
+                self._expect.expect(self._prompt, timeout=0.1)
+            except pexpect.TIMEOUT:
+                pass
+        return result
+
     def __reduce__(self):
         """
         EXAMPLES::