Recommend $x syntax if invalid IF or WHILE has ${x}

For example, `${var} == 'value'` fails for NameError if `${var}` is a
string and using `$var == 'value'` avoids that. Fixes #4676.

atest/robot/running/if/invalid_if.robot

@@ -16,12 +16,18 @@ IF with invalid condition
 IF with invalid condition with ELSE
     FAIL    NOT RUN
 
-IF condition with non-existing variable
+IF condition with non-existing ${variable}
+    FAIL    NOT RUN
+
+IF condition with non-existing $variable
     FAIL    NOT RUN
 
 ELSE IF with invalid condition
     NOT RUN    NOT RUN    FAIL    NOT RUN    NOT RUN
 
+Recommend $var syntax if invalid condition contains ${var}
+    FAIL    index=1
+
 IF without END
     FAIL
 
@@ -106,11 +112,12 @@ Non-existing variable in condition causes normal error
 
 *** Keywords ***
 Branch statuses should be
-    [Arguments]    @{statuses}
+    [Arguments]    @{statuses}    ${index}=0
     ${tc} =    Check Test Case    ${TESTNAME}
-    Should Be Equal    ${tc.body[0].status}    FAIL
-    FOR    ${branch}    ${status}    IN ZIP    ${tc.body[0].body}    ${statuses}
+    ${if} =    Set Variable    ${tc.body}[${index}]
+    Should Be Equal    ${if.status}    FAIL
+    FOR    ${branch}    ${status}    IN ZIP    ${if.body}    ${statuses}
         Should Be Equal    ${branch.status}    ${status}
     END
-    Should Be Equal    ${{len($tc.body[0].body)}}    ${{len($statuses)}}
+    Should Be Equal    ${{len($if.body)}}    ${{len($statuses)}}
     RETURN    ${tc}

atest/robot/running/if/invalid_inline_if.robot

@@ -103,7 +103,12 @@ Assign when ELSE IF branch is empty
 Assign when ELSE branch is empty
     FAIL    NOT RUN
 
-Assign with RETURN
+Control structures are allowed
+    [Template]    NONE
+    ${tc} =    Check Test Case    ${TESTNAME}
+    Check IF/ELSE Status    NOT RUN    PASS    root=${tc.body[0].body[0]}
+
+Control structures are not allowed with assignment
     [Template]    NONE
     ${tc} =    Check Test Case    ${TESTNAME}
     Check IF/ELSE Status    FAIL    NOT RUN    root=${tc.body[0].body[0]}

atest/robot/running/while/invalid_while.robot

@@ -14,12 +14,18 @@ Multiple conditions
 Invalid condition
     Check Invalid WHILE Test Case
 
-Invalid condition on second round
-    Check Test Case    ${TEST NAME}
+Non-existing ${variable} in condition
+    Check Invalid WHILE Test Case
 
-Non-existing variable in condition
+Non-existing $variable in condition
     Check Invalid WHILE Test Case
 
+Recommend $var syntax if invalid condition contains ${var}
+    Check Test Case    ${TEST NAME}
+
+Invalid condition on second round
+    Check Test Case    ${TEST NAME}
+
 No body
     Check Invalid WHILE Test Case    body=False
 

atest/testdata/running/if/invalid_if.robot

@@ -14,29 +14,38 @@ IF without condition with ELSE
     END
 
 IF with invalid condition
-    [Documentation]    FAIL STARTS: Evaluating IF condition failed: Evaluating expression ''123'=123' failed: SyntaxError:
+    [Documentation]    FAIL STARTS:     Invalid IF condition: Evaluating expression ''123'=123' failed: SyntaxError:
     IF    '123'=${123}
         Fail    Should not be run
     END
 
-IF condition with non-existing variable
-    [Documentation]    FAIL Evaluating IF condition failed: Variable '\${ooop}' not found.
+IF condition with non-existing ${variable}
+    [Documentation]    FAIL    Invalid IF condition: Evaluating expression '\${ooop}' failed: Variable '\${ooop}' not found.
     IF    ${ooop}
         Fail    Should not be run
     ELSE IF    ${not evaluated}
         Not run
     END
 
+IF condition with non-existing $variable
+    [Documentation]    FAIL    Invalid IF condition: Evaluating expression '$ooop' failed: Variable '$ooop' not found.
+    IF    $ooop
+        Fail    Should not be run
+    ELSE IF    $not_evaluated
+        Not run
+    END
+
 IF with invalid condition with ELSE
-    [Documentation]    FAIL Evaluating IF condition failed: Evaluating expression 'ooops' failed: NameError: name 'ooops' is not defined nor importable as module
+    [Documentation]    FAIL     Invalid IF condition: \
+    ...    Evaluating expression 'ooops' failed: NameError: name 'ooops' is not defined nor importable as module
     IF    ooops
         Fail    Should not be run
     ELSE
         Fail    Should not be run
     END
 
 ELSE IF with invalid condition
-    [Documentation]    FAIL STARTS: Evaluating ELSE IF condition failed: Evaluating expression '1/0' failed: ZeroDivisionError:
+    [Documentation]    FAIL    STARTS: Invalid ELSE IF condition: Evaluating expression '1/0' failed: ZeroDivisionError:
     IF    False
         Fail    Should not be run
     ELSE IF    False
@@ -49,6 +58,18 @@ ELSE IF with invalid condition
         Fail    Should not be run
     END
 
+Recommend $var syntax if invalid condition contains ${var}
+    [Documentation]    FAIL    Invalid IF condition: \
+    ...    Evaluating expression 'x == 'x'' failed: NameError: name 'x' is not defined nor importable as module
+    ...
+    ...    Variables in the original expression '\${x} == 'x'' were resolved before the expression was evaluated. \
+    ...    Try using '$x == 'x'' syntax to avoid that. See Evaluating Expressions appendix in Robot Framework User Guide for more details.
+    ${x} =    Set Variable    x
+    IF    ${x} == 'x'
+        Fail    Shouldn't be run
+    END
+
+
 IF without END
     [Documentation]    FAIL    IF must have closing END.
     IF    ${True}
@@ -221,14 +242,14 @@ Invalid condition causes normal error
     [Documentation]    FAIL    Teardown failed:
     ...    Several failures occurred:
     ...
-    ...    1) Evaluating IF condition failed: Evaluating expression 'bad in teardown' failed: NameError: name 'bad' is not defined nor importable as module
+    ...    1) Invalid IF condition: Evaluating expression 'bad in teardown' failed: NameError: name 'bad' is not defined nor importable as module
     ...
     ...    2) Should be run in teardown
     TRY
         IF    bad
             Fail    Should not be run
         END
-    EXCEPT    Evaluating IF condition failed: Evaluating expression 'bad' failed: NameError: name 'bad' is not defined nor importable as module
+    EXCEPT    Invalid IF condition: Evaluating expression 'bad' failed: NameError: name 'bad' is not defined nor importable as module
         No Operation
     END
     [Teardown]    Invalid condition
@@ -237,14 +258,14 @@ Non-existing variable in condition causes normal error
     [Documentation]    FAIL    Teardown failed:
     ...    Several failures occurred:
     ...
-    ...    1) Evaluating IF condition failed: Variable '\${bad}' not found.
+    ...    1) Invalid IF condition: Evaluating expression '\${oops}' failed: Variable '\${oops}' not found.
     ...
     ...    2) Should be run in teardown
     TRY
         IF    ${bad}
             Fail    Should not be run
         END
-    EXCEPT    Evaluating IF condition failed: Variable '\${bad}' not found.
+    EXCEPT    Invalid IF condition: Evaluating expression '\${bad}' failed: Variable '\${bad}' not found.
         No Operation
     END
     [Teardown]    Non-existing variable in condition
@@ -259,7 +280,7 @@ Invalid condition
     Fail    Should be run in teardown
 
 Non-existing variable in condition
-    IF    ${bad}
+    IF    ${oops}
         Fail    Should not be run
     END
     Fail    Should be run in teardown

atest/testdata/running/if/invalid_inline_if.robot

@@ -1,160 +1,174 @@
 *** Test Cases ***
 Invalid condition
-    [Documentation]    FAIL Evaluating IF condition failed: Evaluating expression 'ooops' failed: NameError: name 'ooops' is not defined nor importable as module
+    [Documentation]    FAIL    Invalid IF condition: \
+    ...    Evaluating expression 'ooops' failed: NameError: name 'ooops' is not defined nor importable as module
     IF    ooops    Not run    ELSE    Not run either
 
 Condition with non-existing variable
-    [Documentation]    FAIL Evaluating IF condition failed: Variable '\${ooops}' not found.
+    [Documentation]    FAIL    Invalid IF condition: \
+    ...    Evaluating expression '${ooops}' failed: Variable '\${ooops}' not found.
     IF    ${ooops}    Not run
 
 Invalid condition with other error
-    [Documentation]    FAIL ELSE branch cannot be empty.
+    [Documentation]    FAIL     ELSE branch cannot be empty.
     IF    bad    Not run    ELSE
 
 Empty IF
-    [Documentation]    FAIL Multiple errors:
+    [Documentation]    FAIL
+    ...    Multiple errors:
     ...    - IF must have a condition.
     ...    - IF branch cannot be empty.
     ...    - IF must have closing END.
     IF
 
 IF without branch
-    [Documentation]    FAIL Multiple errors:
+    [Documentation]    FAIL
+    ...    Multiple errors:
     ...    - IF branch cannot be empty.
     ...    - IF must have closing END.
     IF    True
 
 IF without branch with ELSE IF
-    [Documentation]    FAIL IF branch cannot be empty.
+    [Documentation]    FAIL    IF branch cannot be empty.
     IF    True    ELSE IF    True    Not run
 
 IF without branch with ELSE
-    [Documentation]    FAIL IF branch cannot be empty.
+    [Documentation]    FAIL    IF branch cannot be empty.
     IF    True    ELSE    Not run
 
 IF followed by ELSE IF
-    [Documentation]    FAIL STARTS: Evaluating IF condition failed: Evaluating expression 'ELSE IF' failed:
+    [Documentation]    FAIL    STARTS: Invalid IF condition: Evaluating expression 'ELSE IF' failed:
     IF    ELSE IF   False    Not run
 
 IF followed by ELSE
-    [Documentation]    FAIL Evaluating IF condition failed: Evaluating expression 'ELSE' failed: NameError: name 'ELSE' is not defined nor importable as module
+    [Documentation]    FAIL    Invalid IF condition: \
+    ...    Evaluating expression 'ELSE' failed: NameError: name 'ELSE' is not defined nor importable as module
     IF    ELSE    Not run
 
 Empty ELSE IF 1
-    [Documentation]    FAIL Multiple errors:
+    [Documentation]    FAIL
+    ...    Multiple errors:
     ...    - ELSE IF must have a condition.
     ...    - ELSE IF branch cannot be empty.
     IF    False    Not run    ELSE IF
 
 Empty ELSE IF 2
-    [Documentation]    FAIL Evaluating ELSE IF condition failed: Evaluating expression 'ELSE' failed: NameError: name 'ELSE' is not defined nor importable as module
+    [Documentation]    FAIL    Invalid ELSE IF condition: \
+    ...    Evaluating expression 'ELSE' failed: NameError: name 'ELSE' is not defined nor importable as module
     IF    False    Not run    ELSE IF    ELSE    Not run
 
 ELSE IF without branch 1
-    [Documentation]   FAIL ELSE IF branch cannot be empty.
+    [Documentation]    FAIL    ELSE IF branch cannot be empty.
     IF    False    Not run    ELSE IF    False
 
 ELSE IF without branch 2
-    [Documentation]   FAIL ELSE IF branch cannot be empty.
+    [Documentation]    FAIL    ELSE IF branch cannot be empty.
     IF    False    Not run    ELSE IF    False    ELSE    Not run
 
 Empty ELSE
-    [Documentation]    FAIL ELSE branch cannot be empty.
+    [Documentation]    FAIL    ELSE branch cannot be empty.
     IF    True    Not run    ELSE IF    True    Not run    ELSE
 
 ELSE IF after ELSE 1
-    [Documentation]    FAIL ELSE IF not allowed after ELSE.
+    [Documentation]    FAIL    ELSE IF not allowed after ELSE.
     IF    True    Not run    ELSE    Not run    ELSE IF    True    Not run
 
 ELSE IF after ELSE 2
-    [Documentation]    FAIL ELSE IF not allowed after ELSE.
+    [Documentation]    FAIL    ELSE IF not allowed after ELSE.
     IF    True    Not run    ELSE    Not run    ELSE IF    True    Not run     ELSE IF    True    Not run
 
 Multiple ELSEs 1
-    [Documentation]    FAIL Only one ELSE allowed.
+    [Documentation]    FAIL    Only one ELSE allowed.
     IF    True    Not run    ELSE    Not run    ELSE    Not run
 
 Multiple ELSEs 2
-    [Documentation]    FAIL Only one ELSE allowed.
+    [Documentation]    FAIL    Only one ELSE allowed.
     IF    True    Not run    ELSE    Not run    ELSE    Not run    ELSE    Not run
 
 Nested IF 1
-    [Documentation]    FAIL Inline IF cannot be nested.
+    [Documentation]    FAIL    Inline IF cannot be nested.
     IF    True    IF    True    Not run
 
 Nested IF 2
-    [Documentation]    FAIL Inline IF cannot be nested.
+    [Documentation]    FAIL    Inline IF cannot be nested.
     IF    True    Not run    ELSE    IF    True    Not run
 
 Nested IF 3
-    [Documentation]    FAIL Inline IF cannot be nested.
+    [Documentation]    FAIL    Inline IF cannot be nested.
     IF                True    IF    True    Not run
     ...    ELSE IF    True    IF    True    Not run
     ...    ELSE               IF    True    Not run
 
 Nested FOR
-    [Documentation]    FAIL 'For' is a reserved keyword. It must be an upper case 'FOR' when used as a marker.
+    [Documentation]    FAIL    'For' is a reserved keyword. It must be an upper case 'FOR' when used as a marker.
     IF    True    FOR    ${x}    IN    @{stuff}
 
 Unnecessary END
-    [Documentation]    FAIL Keyword 'BuiltIn.No Operation' expected 0 arguments, got 1.
+    [Documentation]    FAIL    Keyword 'BuiltIn.No Operation' expected 0 arguments, got 1.
     IF    True     No operation    ELSE    Log    END
     IF    False    Not run         ELSE    No operation    END
 
 Invalid END after inline header
-    [Documentation]    FAIL END is not allowed in this context.
+    [Documentation]    FAIL    END is not allowed in this context.
     IF    True    Log    Executed inside inline IF
         Log   Executed outside IF
     END
 
 Assign in IF branch
-    [Documentation]    FAIL Inline IF branches cannot contain assignments.
+    [Documentation]    FAIL    Inline IF branches cannot contain assignments.
     IF    False    ${x} =    Whatever
 
 Assign in ELSE IF branch
-    [Documentation]    FAIL Inline IF branches cannot contain assignments.
+    [Documentation]    FAIL    Inline IF branches cannot contain assignments.
     IF    False    Keyword    ELSE IF   False    ${x} =    Whatever
 
 Assign in ELSE branch
-    [Documentation]    FAIL Inline IF branches cannot contain assignments.
+    [Documentation]    FAIL    Inline IF branches cannot contain assignments.
     IF    False    Keyword    ELSE    ${x} =    Whatever
 
 Invalid assign mark usage
-    [Documentation]    FAIL Assign mark '=' can be used only with the last variable.
+    [Documentation]    FAIL    Assign mark '=' can be used only with the last variable.
     ${x} =    ${y}    IF    True    Create list    x    y
 
 Too many list variables in assign
-    [Documentation]    FAIL Assignment can contain only one list variable.
+    [Documentation]    FAIL    Assignment can contain only one list variable.
     @{x}    @{y} =    IF    True    Create list    x    y    ELSE    Not run
 
 Invalid number of variables in assign
-    [Documentation]    FAIL Cannot set variables: Expected 2 return values, got 3.
+    [Documentation]    FAIL    Cannot set variables: Expected 2 return values, got 3.
     ${x}    ${y} =    IF    False    Create list    x    y     ELSE    Create list    x    y    z
 
 Invalid value for list assign
-    [Documentation]    FAIL Cannot set variable '\@{x}': Expected list-like value, got string.
+    [Documentation]    FAIL    Cannot set variable '\@{x}': Expected list-like value, got string.
     @{x} =    IF    True    Set variable    String is not list
 
 Invalid value for dict assign
-    [Documentation]    FAIL Cannot set variable '\&{x}': Expected dictionary-like value, got string.
+    [Documentation]    FAIL    Cannot set variable '\&{x}': Expected dictionary-like value, got string.
     &{x} =    IF    False    Not run    ELSE    Set variable    String is not dict either
 
 Assign when IF branch is empty
-    [Documentation]    FAIL IF branch cannot be empty.
+    [Documentation]    FAIL    IF branch cannot be empty.
     ${x} =    IF    False
 
 Assign when ELSE IF branch is empty
-    [Documentation]    FAIL ELSE IF branch cannot be empty.
+    [Documentation]    FAIL    ELSE IF branch cannot be empty.
     ${x} =    IF    True    Not run    ELSE IF    True
 
 Assign when ELSE branch is empty
-    [Documentation]    FAIL ELSE branch cannot be empty.
+    [Documentation]    FAIL    ELSE branch cannot be empty.
     ${x} =    IF    True    Not run    ELSE
 
-Assign with RETURN
-    [Documentation]    FAIL Inline IF with assignment can only contain keyword calls.
+Control structures are allowed
+    With RETURN
+
+Control structures are not allowed with assignment
+    [Documentation]    FAIL    Inline IF with assignment can only contain keyword calls.
     Assign with RETURN
 
 *** Keywords ***
+With RETURN
+    IF    False    Fail    Not run    ELSE    RETURN
+    Fail    Not run
+
 Assign with RETURN
     ${x} =    IF    False    RETURN    ELSE    Not run