Add a minimum export implementation

[rnk]

lgtm

llvm/utils/lit/lit/TestRunner.py

for arg in seq:
             result.extend(bs_buf)
 
         if needquote:
             result.extend(bs_buf)
             result.append('"')
 
     return ''.join(result)
 
+# cmd is export or env
+def updateEnv(env, cmd):
+    arg_idx = 1
+    for arg_idx, arg in enumerate(cmd.args[1:]):
+        # Partition the string into KEY=VALUE.
+        key, eq, val = arg.partition('=')
+        # Stop if there was no equals.
+        if eq == '':
+            break
+        env.env[key] = val
+    cmd.args = cmd.args[arg_idx+1:]
+
 def _executeShCmd(cmd, shenv, results, timeoutHelper):
     if timeoutHelper.timeoutReached():
         # Prevent further recursion if the timeout has been hit
         # as we should try avoid launching more processes.
         return None
 
     if isinstance(cmd, ShUtil.Seq):
         if cmd.op == ';':
if cmd.commands[0].args[0] == 'cd':
         if os.path.isabs(newdir):
             shenv.cwd = newdir
         else:
             shenv.cwd = os.path.realpath(os.path.join(shenv.cwd, newdir))
         # The cd builtin always succeeds. If the directory does not exist, the
         # following Popen calls will fail instead.
         return 0
 
+    if cmd.commands[0].args[0] == 'export':
+        if len(cmd.commands) != 1:
+            raise ValueError("'export' cannot be part of a pipeline")
+        if len(cmd.commands[0].args) != 2:
+            raise ValueError("'export' supports only one argument")
+        updateEnv(shenv, cmd.commands[0])
+        return 0
+
     procs = []
     input = subprocess.PIPE
     stderrTempFiles = []
     opened_files = []
     named_temp_files = []
     # To avoid deadlock, we use a single stderr stream for piped
     # output. This is null until we have seen some output using
     # stderr.
     for i,j in enumerate(cmd.commands):
         # Reference the global environment by default.
         cmd_shenv = shenv
         if j.args[0] == 'env':
             # Create a copy of the global environment and modify it for this one
             # command. There might be multiple envs in a pipeline:
             #   env FOO=1 llc < %s | env BAR=2 llvm-mc | FileCheck %s
             cmd_shenv = ShellEnvironment(shenv.cwd, shenv.env)
-            arg_idx = 1
-            for arg_idx, arg in enumerate(j.args[1:]):
-                # Partition the string into KEY=VALUE.
-                key, eq, val = arg.partition('=')
-                # Stop if there was no equals.
-                if eq == '':
-                    break
-                cmd_shenv.env[key] = val
-            j.args = j.args[arg_idx+1:]
+            updateEnv(cmd_shenv, j)
 
         # Apply the redirections, we use (N,) as a sentinel to indicate stdin,
         # stdout, stderr for N equal to 0, 1, or 2 respectively. Redirects to or
         # from a file are represented with a list [file, mode, file-object]
         # where file-object is initially None.
         redirects = [(0,), (1,), (2,)]
         for r in j.redirects:
             if r[0] == ('>',2):