[lit] Check for accidental external command calls

This patch extends lit's test suite to check that lit's internal shell
doesn't accidentally execute internal commands as external commands.
It does so by putting fake failing versions of those commands in
`PATH` while the entire lit test suite is running.  Without the fixes
in D65697 but with its tests, this approach catches accidental
external `env` calls.

Reviewed By: probinson

Differential Revision: https://reviews.llvm.org/D66293

llvm-svn: 369309

Author: jdenny-ornl

llvm/utils/lit/tests/Inputs/fake-externals/cd

@@ -0,0 +1,5 @@
+#!/usr/bin/env python
+
+import fake_external
+
+fake_external.execute(__file__)

llvm/utils/lit/tests/Inputs/fake-externals/diff

@@ -0,0 +1,5 @@
+#!/usr/bin/env python
+
+import fake_external
+
+fake_external.execute(__file__)

llvm/utils/lit/tests/Inputs/fake-externals/env

@@ -0,0 +1,5 @@
+#!/usr/bin/env python
+
+import fake_external
+
+fake_external.execute(__file__)

llvm/utils/lit/tests/Inputs/fake-externals/export

@@ -0,0 +1,5 @@
+#!/usr/bin/env python
+
+import fake_external
+
+fake_external.execute(__file__)

llvm/utils/lit/tests/Inputs/fake-externals/fake_external.py

@@ -0,0 +1,7 @@
+import os
+import sys
+
+def execute(fileName):
+  sys.stderr.write("error: external '{}' command called unexpectedly\n"
+                   .format(os.path.basename(fileName)));
+  sys.exit(1)

llvm/utils/lit/tests/Inputs/fake-externals/mkdir

@@ -0,0 +1,5 @@
+#!/usr/bin/env python
+
+import fake_external
+
+fake_external.execute(__file__)

llvm/utils/lit/tests/Inputs/fake-externals/rm

@@ -0,0 +1,5 @@
+#!/usr/bin/env python
+
+import fake_external
+
+fake_external.execute(__file__)

llvm/utils/lit/tests/lit.cfg

@@ -75,3 +75,14 @@ else:
 if not llvm_config:
   if sys.platform.startswith('win') or sys.platform.startswith('cygwin'):
     config.available_features.add('system-windows')
+
+# For each of lit's internal shell commands ('env', 'cd', 'diff', etc.), put
+# a fake command that always fails at the start of PATH.  This helps us check
+# that we always use lit's internal version rather than some external version
+# that might not be present or behave correctly on all platforms.  Don't do
+# this for 'echo' because an external version is used when it appears in a
+# pipeline.  Don't do this for ':' because it doesn't appear to be a valid file
+# name under Windows.
+test_bin = os.path.join(os.path.dirname(__file__), 'Inputs', 'fake-externals')
+config.environment['PATH'] = os.path.pathsep.join((test_bin,
+                                                   config.environment['PATH']))