[lldb/Python] Fix the infinitely looping prompt bug

[JDevlieghere]

Summary

This bug has been bothering me for a while. When you do something like the commands below, you'd get bombarded by a wall of Python command prompts (>>> ).

$ echo 'foo' | ./bin/lldb -o script

$ cat /tmp/script
script
print("foo")
$ lldb --source /tmp/script

The issue is that our custom input reader doesn't handle EOF. According to the Python documentation, file.readline always includes a trailing newline character unless the file ends with an incomplete line. Therefore, checking for the empty string before stripping it tells us if we've read EOF.

[1] https://docs.python.org/2/library/stdtypes.html#file.readline

[JDevlieghere]

Add test

[teemperor]

LGTM, but some documentation would be nice.

lldb/source/Interpreter/embedded_interpreter.py

77

# Empty line from readline indicates EOF

lldb/test/Shell/ScriptInterpreter/Python/eof.test

4

I think this should have a comment that ">>>" is the python interpreter prompt and why we check for it.

lldb/source/Interpreter/embedded_interpreter.py

def get_terminal_size(fd):
     except:
         hw = (0, 0)
     return hw
 
 
 def readfunc_stdio(prompt):
     sys.stdout.write(prompt)
     sys.stdout.flush()
-    return sys.stdin.readline().rstrip()
+    line = sys.stdin.readline()
+    # Readline always includes a trailing newline character unless the file
+    # ends with an incomplete line. An empty line indicates EOF.
+    if not line:
+        raise EOFError
+    return line.rstrip()
 
 
 def run_python_interpreter(local_dict):
     # Pass in the dictionary, for continuity from one session to the next.
     setquit()
     try:
         fd = sys.stdin.fileno()
         interacted = False

lldb/test/Shell/ScriptInterpreter/Python/eof.test

+RUN: echo 'foo' | %lldb -o script | FileCheck %s
+
+# Check that the python interpreter detects the OF and the prompt is printed
+# exactly once.
+CHECK: >>>
+CHECK-NOT: >>>