[thejesh23]

lit's builtin cat now reads stdin for a - operand, as POSIX cat does. This adds a case to the shtest-cat inputs.

Fixes #240058

Assisted-by: Claude Code (claude-opus-5-5). I reviewed the change. I also ran the shtest-cat inputs locally: they fail before the change and pass after it.

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[llvmorg-github-actions]

@llvm/pr-subscribers-testing-tools

Author: Thejesh (thejesh23)

Changes

lit's builtin cat now reads stdin for a - operand, as POSIX cat does. This adds a case to the shtest-cat inputs.

Fixes #240058

Assisted-by: Claude Code (claude-opus-5-5). I reviewed the change. I also ran the shtest-cat inputs locally: they fail before the change and pass after it.

---

Full diff: https://github.com/llvm/llvm-project/pull/240060.diff

2 Files Affected:

• (modified) llvm/utils/lit/lit/builtin_commands/cat.py (+3-1)
• (modified) llvm/utils/lit/tests/Inputs/shtest-cat/cat.txt (+12)

diff --git a/llvm/utils/lit/lit/builtin_commands/cat.py b/llvm/utils/lit/lit/builtin_commands/cat.py
index 2882b79f572fd9..bf5430d037e038 100644
--- a/llvm/utils/lit/lit/builtin_commands/cat.py
+++ b/llvm/utils/lit/lit/builtin_commands/cat.py
@@ -71,7 +71,9 @@ def run(argv, stdin, stdout, stderr, cwd):
 
         contents = None
         is_text = False
-        if platform.system() == "OS/390":
+        if filename == "-":
+            contents = stdin.read()
+        elif platform.system() == "OS/390":
             try:
                 with open(path, "r") as fileToCat:
                     contents = fileToCat.read()
diff --git a/llvm/utils/lit/tests/Inputs/shtest-cat/cat.txt b/llvm/utils/lit/tests/Inputs/shtest-cat/cat.txt
index c5b5d247c2f959..0f7a81fe168e89 100644
--- a/llvm/utils/lit/tests/Inputs/shtest-cat/cat.txt
+++ b/llvm/utils/lit/tests/Inputs/shtest-cat/cat.txt
@@ -74,3 +74,15 @@
 ## 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
+
+## Test that cat reads stdin in place of a "-" operand.
+# RUN: rm -rf %t
+# RUN: mkdir -p %t
+# RUN: echo "abcdefgh" > %t/temp1.write
+# RUN: echo "mnopqrst" > %t/temp2.write
+# RUN: echo "efghijkl" | cat %t/temp1.write - %t/temp2.write | \
+# RUN:      FileCheck --check-prefix=DASH-CAT-OUTPUT --implicit-check-not={{.}} \
+# RUN:      --match-full-lines --strict-whitespace %s
+#      DASH-CAT-OUTPUT:abcdefgh
+# DASH-CAT-OUTPUT-NEXT:efghijkl
+# DASH-CAT-OUTPUT-NEXT:mnopqrst