[lit] Ensure ulimit does not persist across tests

When constructing a container in a default argument in Python, we
actually end up with a reference to the same default container for every
invocation of the function. Given this happened with the ulimit variable
in ShellEnvironment, we ended up persisting limits across tests. This
would cause some LLVM tests to fail, particularly jitlink and dsymutil
tests, if they ended up running after the one clang test that uses
ulimit -v to set a maximum amount of memory that can be allocated. This
patch fixes that behavior by constructing the dict inside the function
to ensure we get a new instance and adds test coverage.

Author: boomanaiden154

llvm/utils/lit/lit/TestRunner.py

@@ -92,12 +92,12 @@ class ShellEnvironment(object):
     we maintain a dir stack for pushd/popd.
     """
 
-    def __init__(self, cwd, env, umask=-1, ulimit={}):
+    def __init__(self, cwd, env, umask=-1, ulimit=None):
         self.cwd = cwd
         self.env = dict(env)
         self.umask = umask
         self.dirStack = []
-        self.ulimit = ulimit
+        self.ulimit = ulimit if ulimit else {}
 
     def change_dir(self, newdir):
         if os.path.isabs(newdir):

llvm/utils/lit/tests/Inputs/shtest-ulimit/ulimit_reset.txt

@@ -0,0 +1,3 @@
+# RUN: %{python} %S/print_limits.py
+# Fail the test so that we can assert on the output.
+# RUN: not echo return

llvm/utils/lit/tests/shtest-ulimit.py

@@ -5,9 +5,9 @@
 # as well.
 # UNSUPPORTED: system-windows, system-solaris
 
-# RUN: not %{lit} -a -v %{inputs}/shtest-ulimit | FileCheck %s
+# RUN: not %{lit} -a -v %{inputs}/shtest-ulimit --order=lexical | FileCheck %s
 
-# CHECK: -- Testing: 2 tests{{.*}}
+# CHECK: -- Testing: 3 tests{{.*}}
 
 # CHECK-LABEL: FAIL: shtest-ulimit :: ulimit-bad-arg.txt ({{[^)]*}})
 # CHECK: ulimit -n
@@ -16,3 +16,6 @@
 # CHECK-LABEL: FAIL: shtest-ulimit :: ulimit_okay.txt ({{[^)]*}})
 # CHECK: ulimit -n 50
 # CHECK: RLIMIT_NOFILE=50
+
+# CHECK-LABEL: FAIL: shtest-ulimit :: ulimit_reset.txt ({{[^)]*}})
+# CHECK-NOT: RLIMIT_NOFILE=50