Add more pre-run asserts for the DirCompletionAbsolute test

[teemperor]

Summary

The DirCompletionAbsolute is still randomly failing on the nodes even after D50722, so this patch adds more asserts
that verify certain properties on which the actual completion implementation relies on.

The first assert checks that the directory we complete on actually exists. If the directory doesn't exist on the
next CI failure, this assert should catch it and we know that the 0 matches come from a missing base directory.

The second assert is just checking that we are below the PATH_MAX limit that the completion checks against.
This check could randomly fail if the temporary directories we generate are sometimes longer than PATH_MAX,
and the assert can tell us that this is the reason we failed (instead of the mysterious '0 matches').

(As a sidenote: We shouldn't be checking against PATH_MAX anyway in the code (as this is just wrong). Also
the disk completion API really needs a better error mechanism than returning 0 on both error or no-results.)

[aprantl]

unittests/Interpreter/TestCompletion.cpp

171 ↗

(On Diff #161999)

This looks like it's now a line too far below?

[teemperor]

• Moved asserts to the right position.

[teemperor]

unittests/Interpreter/TestCompletion.cpp

171 ↗

(On Diff #161999)

Jep, nice catch! Thanks!

[stella.stamenova]

This does not build correctly on Windows (at least not in our environment). Here are the two errors:

[error]llvm\tools\lldb\unittests\interpreter\testcompletion.cpp(168,0): Error C2065: 'PATH_MAX': undeclared identifier
[error]llvm\tools\lldb\unittests\interpreter\testcompletion.cpp(168,0): Error C2512: 'testing::AssertionResult': no appropriate default constructor available

I haven't had an opportunity to investigate further yet.

[teemperor]

@stella.stamenova Sorry, forgot about Windows here. Just fixed it in r340652.

[stella.stamenova]

In D51111#1212956, @teemperor wrote:

@stella.stamenova Sorry, forgot about Windows here. Just fixed it in r340652.

Thank you!

lldb/trunk/unittests/Interpreter/TestCompletion.cpp

TEST_F(CompletionTest, DirCompletionAbsolute) {
 
   std::string Prefixes[] = {(Twine(BaseDir) + "/").str(), ""};
 
   StandardTildeExpressionResolver Resolver;
   StringList Results;
 
   // When a directory is specified that doesn't end in a slash, it searches
   // for that directory, not items under it.
+  // Sanity check that the path we complete on exists and isn't too long.
+  ASSERT_TRUE(llvm::sys::fs::exists(BaseDir));
+  ASSERT_LE(BaseDir.size(), static_cast<size_t>(PATH_MAX));
   size_t Count =
       CommandCompletions::DiskDirectories(BaseDir, Results, Resolver);
   ASSERT_EQ(1u, Count);
   ASSERT_EQ(Count, Results.GetSize());
   EXPECT_TRUE(HasEquivalentFile(BaseDir, Results));
 
   // When the same directory ends with a slash, it finds all children.
   Count = CommandCompletions::DiskDirectories(Prefixes[0], Results, Resolver);