Rule/undefined argument value

robocop/checkers/misc.py

@@ -855,10 +855,10 @@ def comma_separated_list(value: str) -> list[str]:
         optionally overwrite this default.
 
         When you use an argument default, you should be as clear as possible. This improves the
-        readability of your code. The syntax `${argument}=` is unclear unless you happen to know
-        that it is technically equivalent to `${argument}=${EMPTY}`. To prevent people from
+        readability of your code. The syntax ``${argument}=`` is unclear unless you happen to know
+        that it is technically equivalent to ``${argument}=${EMPTY}``. To prevent people from
         misreading your keyword arguments, explicitly state that the value is empty using the
-        built-in `${EMPTY}` variable.
+        built-in ``${EMPTY}`` variable.
 
         Example of a rule violation::
 
@@ -867,6 +867,29 @@ def comma_separated_list(value: str) -> list[str]:
                 [Arguments]    ${argument_name}=
         """,
     ),
+    "0933": DefaultRule(
+        rule_id="0933",
+        name="undefined-argument-value",
+        msg="Undefined argument value, use {{ arg_name }}=${EMPTY} instead",
+        severity=RuleSeverity.ERROR,
+        added_in_version="5.7.0",
+        docs="""
+        When calling a keyword, it can accept named arguments.
+
+        When you call a keyword, you should be as clear as possible. This improves the
+        readability of your code. The syntax ``argument=`` is unclear unless you happen to know
+        that it is technically equivalent to ``argument=${EMPTY}``. To prevent people from
+        misreading your keyword arguments, explicitly state that the value is empty using the
+        built-in ``${EMPTY}`` variable.
+
+        If your argument is falsly flagged by this rule, escape the ``=`` character in your argument
+        value by like so: ``\\=``.
+
+        Example of a rule violation::
+
+            My Amazing Keyword    argument_name=
+        """,
+    ),
 }
 
 
@@ -1965,7 +1988,10 @@ def _report(self, rule_name: str, node):
 
 
 class UndefinedArgumentDefaultChecker(VisitorChecker):
-    reports = ("undefined-argument-default",)
+    reports = (
+        "undefined-argument-default",
+        "undefined-argument-value",
+    )
 
     def visit_Arguments(self, node: Arguments):  # noqa: N802
         for token in node.get_tokens(Token.ARGUMENT):
@@ -1989,3 +2015,31 @@ def visit_Arguments(self, node: Arguments):  # noqa: N802
                     end_col=token.col_offset + len(token.value) + 1,
                     arg_name=arg_name + "}",
                 )
+
+    def visit_KeywordCall(self, node: KeywordCall):  # noqa: N802
+        for token in node.get_tokens(Token.ARGUMENT):
+            arg = token.value
+
+            if "=" not in arg or arg.startswith("="):
+                # Is a positional arg
+                continue
+
+            arg_name, default_val = arg.split("=", maxsplit=1)
+            if arg_name.endswith("\\"):
+                # `=` is escaped
+                continue
+
+            if default_val != "":
+                # Has a value
+                continue
+
+            # Falsly triggers if a positional argument ends with `=`
+            # The language server has the same behavior
+            self.report(
+                "undefined-argument-value",
+                node=token,
+                lineno=token.lineno,
+                col=token.col_offset + 1,
+                end_col=token.col_offset + len(token.value) + 1,
+                arg_name=arg_name,
+            )

tests/atest/rules/misc/undefined_argument_value/expected_output.txt

@@ -0,0 +1,6 @@
+test.robot:3:12 [E] 0933 Undefined argument value, use message=${EMPTY} instead
+test.robot:4:12 [E] 0933 Undefined argument value, use message=${EMPTY} instead
+test.robot:4:24 [E] 0933 Undefined argument value, use level=${EMPTY} instead
+test.robot:5:27 [E] 0933 Undefined argument value, use level=${EMPTY} instead
+test.robot:6:12 [E] 0933 Undefined argument value, use A great log message=${EMPTY} instead
+test.robot:7:12 [E] 0933 Undefined argument value, use A great log message =${EMPTY} instead

tests/atest/rules/misc/undefined_argument_value/test.robot

@@ -0,0 +1,20 @@
+*** Test Cases ***
+With undefined value
+    Log    message=
+    Log    message=    level=
+    Log    Hello world    level=    html=${True}
+    Log    A great log message=
+    Log    A great log message =
+
+With escaped equals sign
+    Log    A great log message \=
+    Log    A great log message\=
+    Log    Hello\=world
+    Log    mess\=age=foo
+
+With defined values
+    Log    Hello = world
+    Log    message=Hello world
+    Log    message==
+    Log    =
+    Log    = amazing!

tests/atest/rules/misc/undefined_argument_value/test_rule.py

@@ -0,0 +1,6 @@
+from tests.atest.utils import RuleAcceptance
+
+
+class TestRuleAcceptance(RuleAcceptance):
+    def test_rule(self):
+        self.check_rule(src_files=["test.robot"], expected_file="expected_output.txt")