Support Path with Split/Join Command Line.

Fixes #4749.

atest/robot/standard_libraries/process/commandline.robot

@@ -15,6 +15,9 @@ Split command line with unbalanced quotes
 Split command line with escaping
     Check Test Case    ${TESTNAME}
 
+Split command line with pathlib.Path
+    Check Test Case    ${TESTNAME}
+
 Join command line basics
     Check Test Case    ${TESTNAME}
 
@@ -23,3 +26,6 @@ Join command line with internal quotes
 
 Join command line with escaping
     Check Test Case    ${TESTNAME}
+
+Join command line with non-strings
+    Check Test Case    ${TESTNAME}

atest/testdata/standard_libraries/process/commandline.robot

@@ -64,6 +64,10 @@ Split command line with escaping
     \\\\\\"\\\\                       \\"\\                        escaping=True
     "\\\\\\"\\\\"                     \\"\\                        escaping=True
 
+Split command line with pathlib.Path
+    [Template]    Split command line should succeed
+    ${{pathlib.Path($TEMPDIR)}}    ${TEMPDIR}
+
 Join command line basics
     [Template]    Join command line should succeed
     FOR    ${i}    IN RANGE    ${BASICS}
@@ -82,6 +86,11 @@ Join command line with escaping
     \\\\\\"                           \\"
     \\\\\\\\\\"                       \\\\"
 
+Join command line with non-strings
+    [Template]    Join command line should succeed
+    ${TEMPDIR}          ${{pathlib.Path($TEMPDIR)}}
+    -n 42 ${TEMPDIR}    -n    ${42}    ${{pathlib.Path($TEMPDIR)}}
+
 *** Keywords ***
 Split command line should succeed
     [Arguments]    ${input}    @{expected}    &{config}
@@ -90,7 +99,8 @@ Split command line should succeed
 
 Split command line should fail
     [Arguments]    ${input}    ${error}=No closing quotation
-    Run keyword and expect error    ValueError: Parsing '${input}' failed: ${error}
+    Run keyword and expect error
+    ...    ValueError: Parsing '${input}' failed: ${error}
     ...    Split command line    ${input}
 
 Join command line should succeed

src/robot/libraries/Process.py

@@ -768,10 +768,12 @@ def split_command_line(self, args, escaping=False):
         """Splits command line string into a list of arguments.
 
         String is split from spaces, but argument surrounded in quotes may
-        contain spaces in them. If ``escaping`` is given a true value, then
-        backslash is treated as an escape character. It can escape unquoted
-        spaces, quotes inside quotes, and so on, but it also requires using
-        double backslashes when using Windows paths.
+        contain spaces in them.
+
+        If ``escaping`` is given a true value, then backslash is treated as
+        an escape character. It can escape unquoted spaces, quotes inside
+        quotes, and so on, but it also requires using doubling backslashes
+        in Windows paths and elsewhere.
 
         Examples:
         | @{cmd} = | Split Command Line | --option "value with spaces" |
@@ -786,7 +788,7 @@ def join_command_line(self, *args):
         arguments containing spaces are surrounded with quotes, and possible
         quotes are escaped with a backslash.
 
-        If this keyword is given only one argument and that is a list like
+        If this keyword is given only one argument and that is a list-like
         object, then the values of that list are joined instead.
 
         Example:
@@ -795,7 +797,7 @@ def join_command_line(self, *args):
         """
         if len(args) == 1 and is_list_like(args[0]):
             args = args[0]
-        return subprocess.list2cmdline(args)
+        return subprocess.list2cmdline(str(a) for a in args)
 
 
 class ExecutionResult:

src/robot/utils/argumentparser.py

@@ -21,6 +21,7 @@
 import sys
 import string
 import warnings
+from pathlib import Path
 
 from robot.errors import DataError, Information, FrameworkError
 from robot.version import get_full_version
@@ -32,6 +33,8 @@
 
 
 def cmdline2list(args, escaping=False):
+    if isinstance(args, Path):
+        return [str(args)]
     lexer = shlex.shlex(args, posix=True)
     if is_falsy(escaping):
         lexer.escape = ''