[test] Use realpath consistently for test root file paths.

[rupprecht]

Summary

LLDB tests assume that tests are in the test tree (the LLDB_TEST_SRC env variable, configured by dotest.py).
If this assertion doesn't hold, tests fail in strange ways. An early place this goes wrong is in compute_mydir which does a simple length-based substring to get the relative path. Later, we use that path to chdir to. If the test file and test tree don't agree in realpath-ness (and therefore length), this will be a cryptic error of chdir-ing to a directory that does not exist.

The actual discrepency is that the places we look for use_lldb_suite.py don't use a realpath, but dotest.py does (see initialization of configuration.testdirs).

It doesn't particularly matter whether we use realpath or abspath to canonicalize things, but many places end up with implicit dependencies on the canonicalized pwd being a realpath, so make them realpath consistently. Also, in the compute_mydir method mentioned, raise an error if the path types don't agree.

[JDevlieghere]

lldb/packages/Python/lldbsuite/test/lldbtest.py

499–504

While you are here... can you change this to pass the source directory trough the configuration?

[rupprecht]

lldb/packages/Python/lldbsuite/test/lldbtest.py

499–504

Absolutely, but in the spirit of small/isolated changes, split off as D85322.

lldb/packages/Python/lldbsuite/__init__.py

 # Module level initialization for the `lldbsuite` module.
 
 import inspect
 import os
 import sys
 
 
 def find_lldb_root():
-    lldb_root = os.path.dirname(inspect.getfile(inspect.currentframe()))
+    lldb_root = os.path.realpath(
+        os.path.dirname(inspect.getfile(inspect.currentframe())))
     while True:
         parent = os.path.dirname(lldb_root)
         if parent == lldb_root: # dirname('/') == '/'
             raise Exception("use_lldb_suite_root.py not found")
         lldb_root = parent
 
         test_path = os.path.join(lldb_root, "use_lldb_suite_root.py")
         if os.path.isfile(test_path):
             return lldb_root
 
 # lldbsuite.lldb_root refers to the root of the git/svn source checkout
 lldb_root = find_lldb_root()
 
 # lldbsuite.lldb_test_src_root refers to the root of the python test case tree
 # (i.e. the actual unit tests).
 lldb_test_root = os.path.join(lldb_root, "test", "API")

lldb/packages/Python/lldbsuite/test/lldbtest.py

class Base(unittest2.TestCase):
     @staticmethod
     def compute_mydir(test_file):
         '''Subclasses should call this function to correctly calculate the
            required "mydir" attribute as follows:
 
             mydir = TestBase.compute_mydir(__file__)
         '''
         # /abs/path/to/packages/group/subdir/mytest.py -> group/subdir
-        rel_prefix = test_file[len(configuration.test_src_root) + 1:]
-        return os.path.dirname(rel_prefix)
+        lldb_test_src = configuration.test_src_root
+        if not test_file.startswith(lldb_test_src):
+          raise Exception(
+              "Test file '%s' must reside within lldb_test_src "
+              "(which is '%s')." % (test_file, lldb_test_src))
+        return os.path.dirname(os.path.relpath(test_file, start=lldb_test_src))
 
     def TraceOn(self):
         """Returns True if we are in trace mode (tracing detailed test execution)."""
         return traceAlways
 
     def trace(self, *args,**kwargs):
         with recording(self, self.TraceOn()) as sbuf:
             print(*args, file=sbuf, **kwargs)

lldb/test/API/use_lldb_suite.py

 import inspect
 import os
 import sys
 
 
 def find_lldb_root():
-    lldb_root = os.path.dirname(
-        os.path.abspath(inspect.getfile(inspect.currentframe()))
-    )
+    lldb_root = os.path.realpath(
+        os.path.dirname(inspect.getfile(inspect.currentframe())))
     while True:
         parent = os.path.dirname(lldb_root)
         if parent == lldb_root: # dirname('/') == '/'
             raise Exception("use_lldb_suite_root.py not found")
         lldb_root = parent
 
         test_path = os.path.join(lldb_root, "use_lldb_suite_root.py")
         if os.path.isfile(test_path):