Add output.pipe_to_pager() that pipes lines to a pager without creating an intermediate temporary file

osc/output/__init__.py

@@ -1,6 +1,7 @@
 from .key_value_table import KeyValueTable
 from .input import get_user_input
 from .output import get_default_pager
+from .output import pipe_to_pager
 from .output import print_msg
 from .output import run_pager
 from .output import sanitize_text

osc/output/output.py

@@ -2,9 +2,11 @@ import os
 import platform
 import re
 import shlex
+import subprocess
 import sys
 import tempfile
 from typing import Dict
+from typing import List
 from typing import Optional
 from typing import TextIO
 from typing import Union
@@ -170,6 +172,25 @@ def get_default_pager():
     return 'more'
 
 
+def get_pager():
+    """
+    Return (pager, env) where
+        ``pager`` is a list with parsed pager command
+        ``env`` is copy of os.environ() with added variables specific to the pager
+    """
+    env = os.environ.copy()
+    pager = os.getenv("PAGER", default="").strip()
+    pager = pager or get_default_pager()
+
+    # LESS env is not always set and we need -R to display escape sequences properly
+    less_opts = os.getenv("LESS", default="")
+    if "-R" not in less_opts:
+        less_opts += " -R"
+    env["LESS"] = less_opts
+
+    return shlex.split(pager), env
+
+
 def run_pager(message: Union[bytes, str], tmp_suffix: str = ""):
     from ..core import run_external
 
@@ -185,16 +206,29 @@ def run_pager(message: Union[bytes, str], tmp_suffix: str = ""):
         safe_write(tmpfile, message)
         tmpfile.flush()
 
-        env = os.environ.copy()
-
-        pager = os.getenv("PAGER", default="").strip()
-        pager = pager or get_default_pager()
-
-        # LESS env is not always set and we need -R to display escape sequences properly
-        less_opts = os.getenv("LESS", default="")
-        if "-R" not in less_opts:
-            less_opts += " -R"
-        env["LESS"] = less_opts
-
-        cmd = shlex.split(pager) + [tmpfile.name]
+        pager, env = get_pager()
+        cmd = pager + [tmpfile.name]
         run_external(*cmd, env=env)
+
+
+def pipe_to_pager(lines: Union[List[bytes], List[str]], *, add_newlines=False):
+    """
+    Pipe ``lines`` to the pager.
+    If running in a non-interactive terminal, print the data instead.
+    Add a newline after each line if ``add_newlines`` is ``True``.
+    """
+    if not tty.IS_INTERACTIVE:
+        for line in lines:
+            safe_write(sys.stdout, line, add_newline=add_newlines)
+        return
+
+    pager, env = get_pager()
+    with subprocess.Popen(pager, stdin=subprocess.PIPE, encoding="utf-8", env=env) as proc:
+        try:
+            for line in lines:
+                safe_write(proc.stdin, line, add_newline=add_newlines)
+                proc.stdin.flush()
+            proc.stdin.close()
+        except BrokenPipeError:
+            pass
+        proc.wait()