[lit] Remove Python 2 string support (#157979)

There are some code paths within lit that still check what string types
are supported with the aim of being compatible with Python 2 and 3.
Given LLVM's minimum Python version is 3.8 and we do not have any
upstream testing for Python 2, I think we can safely drop this.

Author: boomanaiden154

llvm/utils/lit/lit/TestRunner.py

@@ -899,14 +899,8 @@ def _executeShCmd(cmd, shenv, results, timeoutHelper):
 
         # Replace uses of /dev/null with temporary files.
         if kAvoidDevNull:
-            # In Python 2.x, basestring is the base class for all string (including unicode)
-            # In Python 3.x, basestring no longer exist and str is always unicode
-            try:
-                str_type = basestring
-            except NameError:
-                str_type = str
             for i, arg in enumerate(args):
-                if isinstance(arg, str_type) and kDevNull in arg:
+                if isinstance(arg, str) and kDevNull in arg:
                     f = tempfile.NamedTemporaryFile(delete=False)
                     f.close()
                     named_temp_files.append(f.name)

llvm/utils/lit/lit/llvm/config.py

@@ -233,7 +233,7 @@ def with_environment(self, variable, value, append_path=False):
             # For paths, we should be able to take a list of them and process
             # all of them.
             paths_to_add = value
-            if lit.util.is_string(paths_to_add):
+            if isinstance(paths_to_add, str):
                 paths_to_add = [paths_to_add]
 
             def norm(x):
@@ -262,7 +262,7 @@ def norm(x):
         self.config.environment[variable] = value
 
     def with_system_environment(self, variables, append_path=False):
-        if lit.util.is_string(variables):
+        if isinstance(variables, str):
             variables = [variables]
         for v in variables:
             value = os.environ.get(v)
@@ -404,7 +404,7 @@ def add_tool_substitutions(self, tools, search_dirs=None):
         if not search_dirs:
             search_dirs = [self.config.llvm_tools_dir]
 
-        if lit.util.is_string(search_dirs):
+        if isinstance(search_dirs, str):
             search_dirs = [search_dirs]
 
         tools = [x if isinstance(x, ToolSubst) else ToolSubst(x) for x in tools]

llvm/utils/lit/lit/util.py

@@ -13,22 +13,14 @@
 import threading
 
 
-def is_string(value):
-    try:
-        # Python 2 and Python 3 are different here.
-        return isinstance(value, basestring)
-    except NameError:
-        return isinstance(value, str)
-
-
 def pythonize_bool(value):
     if value is None:
         return False
     if type(value) is bool:
         return value
     if isinstance(value, numbers.Number):
         return value != 0
-    if is_string(value):
+    if isinstance(value, str):
         if value.lower() in ("1", "true", "on", "yes"):
             return True
         if value.lower() in ("", "0", "false", "off", "no"):