[llvm] 7a3fa06 - [lit] Make builtin cat work with stdin

[via llvm-commits]

Author: Aiden Grossman
Date: 2025-09-19T21:43:52-07:00
New Revision: 7a3fa0671b34c067262f14aa07779a1f13908314

URL: https://github.com/llvm/llvm-project/commit/7a3fa0671b34c067262f14aa07779a1f13908314
DIFF: https://github.com/llvm/llvm-project/commit/7a3fa0671b34c067262f14aa07779a1f13908314.diff

LOG: [lit] Make builtin cat work with stdin

cat with no files passed to it is supposed to read from STDIN according
to POSIX. The builtin cat lacking this behavior led to the clang test in
dev-fd-fs.c to fail because it expected this behavior. This is a simple
modification and I do not think it is possible to rewrite the test
without this easily while preserving the semantics around named pipes.

Reviewers: petrhosek, arichardson, ilovepi, cmtice, jh7370

Reviewed By: jh7370, arichardson, ilovepi, cmtice

Pull Request: https://github.com/llvm/llvm-project/pull/158447

Added: 
    

Modified: 
    clang/test/Misc/dev-fd-fs.c
    llvm/utils/lit/lit/builtin_commands/cat.py
    llvm/utils/lit/tests/Inputs/shtest-cat/cat.txt

Removed: 
    


################################################################################
diff  --git a/clang/test/Misc/dev-fd-fs.c b/clang/test/Misc/dev-fd-fs.c
index ea94d950b0716..b989ab8a439cf 100644
--- a/clang/test/Misc/dev-fd-fs.c
+++ b/clang/test/Misc/dev-fd-fs.c
@@ -1,6 +1,5 @@
 // Check that we can operate on files from /dev/fd.
 // REQUIRES: dev-fd-fs
-// REQUIRES: shell
 
 // Check reading from named pipes. We cat the input here instead of redirecting
 // it to ensure that /dev/fd/0 is a named pipe, not just a redirected file.

diff  --git a/llvm/utils/lit/lit/builtin_commands/cat.py b/llvm/utils/lit/lit/builtin_commands/cat.py
index ddab555662045..2797e0cbb4154 100644
--- a/llvm/utils/lit/lit/builtin_commands/cat.py
+++ b/llvm/utils/lit/lit/builtin_commands/cat.py
@@ -49,6 +49,9 @@ def main(argv):
             import os, msvcrt
 
             msvcrt.setmode(sys.stdout.fileno(), os.O_BINARY)
+    if len(filenames) == 0:
+        sys.stdout.write(sys.stdin.read())
+        sys.exit(0)
     for filename in filenames:
         try:
             contents = None

diff  --git a/llvm/utils/lit/tests/Inputs/shtest-cat/cat.txt b/llvm/utils/lit/tests/Inputs/shtest-cat/cat.txt
index 4014b0fca1f24..c5b5d247c2f95 100644
--- a/llvm/utils/lit/tests/Inputs/shtest-cat/cat.txt
+++ b/llvm/utils/lit/tests/Inputs/shtest-cat/cat.txt
@@ -70,3 +70,7 @@
 # NP-CAT-OUTPUT-NEXT:M-HM-IM-JM-KM-LM-MM-NM-OM-PM-QM-RM-SM-TM-UM-VM-WM-XM-YM-ZM-[
 # NP-CAT-OUTPUT-NEXT:M-\M-]M-^M-_M-`M-aM-bM-cM-dM-eM-fM-gM-hM-iM-jM-kM-lM-mM-nM-o
 # NP-CAT-OUTPUT-NEXT:M-pM-qM-rM-sM-tM-uM-vM-wM-xM-yM-zM-{M-|M-}M-~M-^?
+
+## Test that cat will pipe stdin to stdout if no other files are specified.
+# RUN: echo test | cat | FileCheck --check-prefix=CAT-STDIN %s
+# CAT-STDIN: test