A send to Python's REPL runs once, the Enter after the paste, not in it

A one-line send (print(1)) to Python 3.14 stopped at ... and needed another
Enter: its REPL takes a bracketed paste, and an Enter read in the same read
as the paste is part of the paste, one line or not (checked in a real pty).
Into a REPL that asked for bracketed paste, the Enters (two for an open
block) now wait for its next output, its answer to the paste, or 250 ms
with nothing. fs-test runs python3 in a real pty and checks a one-line exec
prints at once; the docs' pty/data recipe says to send the Enter apart.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 22 insertions, 3 deletions

diff --git a/src/exec.zig b/src/exec.zig
index 56e6a2a9..2f279d8e 100644
--- a/src/exec.zig
+++ b/src/exec.zig
@@ -443,6 +443,18 @@ fn routeToRepl(p: *Pardes, from: usize, text: []const u8) Routed {
     return .asked;
 }
 
+const repl_enter_wait_ns: u64 = 250 * std.time.ns_per_ms;
+
+/// Sends the Enters a paste into pane `id`'s REPL is owed: when the REPL
+/// has answered it (`answered`), or once the wait is up.
+pub fn flushReplEnter(p: *Pardes, id: usize, answered: bool) void {
+    const pane = p.panes[id] orelse return;
+    if (pane.repl_enter == 0) return;
+    if (!answered and p.stepped_ns < pane.repl_enter_due_ns) return;
+    for (0..pane.repl_enter) |_| p.emitWrite(id, "\r");
+    pane.repl_enter = 0;
+}
+
 fn pythonBlockOpen(text: []const u8) bool {
     const trimmed = std.mem.trimEnd(u8, text, " \t\n");
     const start = if (std.mem.lastIndexOfScalar(u8, trimmed, '\n')) |nl| nl + 1 else 0;
@@ -475,13 +487,20 @@ pub fn sendToRepl(p: *Pardes, from: usize, to: usize, text: []const u8) void {
         var said: [128]u8 = undefined;
         return p.setMessage(from, std.fmt.bufPrint(&said, "Repl: {d} bytes is more than can be sent at once; send less", .{n}) catch "Repl: too long to send");
     }
+    const pasted = panes.Terminal.bracketedPaste(dst);
     edit.typeToTty(p, to, dst, clean[0..n]);
-    p.emitWrite(to, "\r");
     // A Python block whose last line is indented, or a bare header, is not
     // over at one Enter, pasted into 3.13's REPL or typed into the old one:
     // the blank line a second Enter gives ends it.
-    if ((if (dst.repl) |r| r.lang == python_lang else false) and pythonBlockOpen(clean[0..n]))
-        p.emitWrite(to, "\r");
+    const enters: u8 = if ((if (dst.repl) |r| r.lang == python_lang else false) and pythonBlockOpen(clean[0..n])) 2 else 1;
+    if (pasted) {
+        // An Enter read with the paste is part of it: 3.13's REPL takes it
+        // as a newline in the pasted text, even a one-line one, and waits.
+        // It goes once the REPL has answered the paste (its next output),
+        // or after a moment if nothing comes.
+        dst.repl_enter = enters;
+        dst.repl_enter_due_ns = p.stepped_ns + repl_enter_wait_ns;
+    } else for (0..enters) |_| p.emitWrite(to, "\r");
     // Line by line, a blank line inside a Python block ends the block.
     if (!panes.Terminal.bracketedPaste(dst) and !dst.repl_warned and (if (dst.repl) |r| r.lang == python_lang else false) and
         std.mem.indexOfScalar(u8, text, '\n') != null)