Whenever I create many constants for different purposes in a project, I tend to categorize them by putting a one letter prefix and an underscore in front of the names. Now, I chose the prefix T_ for some constants and noticed that the compiler gave me a warning:
IDE1006: Naming rule violation: Prefix 'T_' is not expected
That made me really curious, since I have no naming rule configured that says anything about that prefix, so I experimented a little. This warning only shows for the letters S and T, both uppercase and lowercase, so other prefixes like A_, b_ or Z_ are allowed. I tried this with local variables, properties, constants, methods and classes, and for all those cases, this rule applies: No uppercase or lowercase T_ or S_ at the start of an identifier. I know there are many cases I didn't test, but I'm pretty sure this is consistent across all sorts of identifiers in C#.
Now the question is, why is that? Are the prefixes T_, t_, S_, s_ used for anything specific internally, or is it a general naming convention that I simply don't know anything about?
I already googled for the specific message about the prefix, or the prefix in general, and I also took a very brief look at the documentation of IDE1006. None of those things yielded any answers.
Since it was requested, here's my .editorconfig:
[*.cs]
# IDE0039: Use local function
dotnet_diagnostic.IDE0039.severity = silent
As you can see, there is nothing naming related here.
And here's my .csproj:
<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<OutputType>Exe</OutputType>
<TargetFramework>net6.0</TargetFramework>
<ImplicitUsings>enable</ImplicitUsings>
<Nullable>enable</Nullable>
</PropertyGroup>
</Project>
And finally, the .editorconfig file generated from my Code Style settings (naming conventions at the very bottom):
# Remove the line below if you want to inherit .editorconfig settings from higher directories
root = true
# C# files
[*.cs]
#### Core EditorConfig Options ####
# Indentation and spacing
indent_size = 4
indent_style = tab
tab_width = 4
# New line preferences
end_of_line = crlf
insert_final_newline = false
#### .NET Coding Conventions ####
# Organize usings
dotnet_separate_import_directive_groups = true
dotnet_sort_system_directives_first = true
file_header_template = unset
# this. and Me. preferences
dotnet_style_qualification_for_event = false:warning
dotnet_style_qualification_for_field = false
dotnet_style_qualification_for_method = false:warning
dotnet_style_qualification_for_property = false:warning
# Language keywords vs BCL types preferences
dotnet_style_predefined_type_for_locals_parameters_members = true:warning
dotnet_style_predefined_type_for_member_access = true:warning
# Parentheses preferences
dotnet_style_parentheses_in_arithmetic_binary_operators = always_for_clarity:suggestion
dotnet_style_parentheses_in_other_binary_operators = always_for_clarity:suggestion
dotnet_style_parentheses_in_other_operators = never_if_unnecessary:suggestion
dotnet_style_parentheses_in_relational_binary_operators = always_for_clarity:suggestion
# Modifier preferences
dotnet_style_require_accessibility_modifiers = for_non_interface_members
# Expression-level preferences
dotnet_style_coalesce_expression = true:warning
dotnet_style_collection_initializer = true:warning
dotnet_style_explicit_tuple_names = true:warning
dotnet_style_namespace_match_folder = true
dotnet_style_null_propagation = true:warning
dotnet_style_object_initializer = true:warning
dotnet_style_operator_placement_when_wrapping = beginning_of_line
dotnet_style_prefer_auto_properties = true:warning
dotnet_style_prefer_compound_assignment = true:warning
dotnet_style_prefer_conditional_expression_over_assignment = true:warning
dotnet_style_prefer_conditional_expression_over_return = true:warning
dotnet_style_prefer_inferred_anonymous_type_member_names = true:warning
dotnet_style_prefer_inferred_tuple_names = true:warning
dotnet_style_prefer_is_null_check_over_reference_equality_method = true:warning
dotnet_style_prefer_simplified_boolean_expressions = true:warning
dotnet_style_prefer_simplified_interpolation = true
# Field preferences
dotnet_style_readonly_field = true:warning
# Parameter preferences
dotnet_code_quality_unused_parameters = all:warning
# Suppression preferences
dotnet_remove_unnecessary_suppression_exclusions = none
# New line preferences
dotnet_style_allow_multiple_blank_lines_experimental = true
dotnet_style_allow_statement_immediately_after_block_experimental = true
#### C# Coding Conventions ####
# var preferences
csharp_style_var_elsewhere = false:warning
csharp_style_var_for_built_in_types = false:warning
csharp_style_var_when_type_is_apparent = false:warning
# Expression-bodied members
csharp_style_expression_bodied_accessors = true:warning
csharp_style_expression_bodied_constructors = true:warning
csharp_style_expression_bodied_indexers = true:warning
csharp_style_expression_bodied_lambdas = true:warning
csharp_style_expression_bodied_local_functions = true:warning
csharp_style_expression_bodied_methods = true:warning
csharp_style_expression_bodied_operators = true:warning
csharp_style_expression_bodied_properties = true:warning
# Pattern matching preferences
csharp_style_pattern_matching_over_as_with_null_check = true:warning
csharp_style_pattern_matching_over_is_with_cast_check = true:warning
csharp_style_prefer_extended_property_pattern = true
csharp_style_prefer_not_pattern = true:warning
csharp_style_prefer_pattern_matching = true:warning
csharp_style_prefer_switch_expression = true:warning
# Null-checking preferences
csharp_style_conditional_delegate_call = true:warning
# Modifier preferences
csharp_prefer_static_local_function = true:warning
csharp_preferred_modifier_order = public,private,protected,internal,static,extern,new,virtual,abstract,sealed,override,readonly,unsafe,volatile,async
# Code-block preferences
csharp_prefer_braces = false:warning
csharp_prefer_simple_using_statement = true:warning
csharp_style_namespace_declarations = file_scoped:warning
# Expression-level preferences
csharp_prefer_simple_default_expression = true:warning
csharp_style_deconstructed_variable_declaration = true
csharp_style_implicit_object_creation_when_type_is_apparent = true:warning
csharp_style_inlined_variable_declaration = true:warning
csharp_style_prefer_index_operator = true:warning
csharp_style_prefer_local_over_anonymous_function = true:warning
csharp_style_prefer_null_check_over_type_check = true:warning
csharp_style_prefer_range_operator = true:warning
csharp_style_prefer_tuple_swap = true
csharp_style_throw_expression = true:warning
csharp_style_unused_value_assignment_preference = discard_variable:warning
csharp_style_unused_value_expression_statement_preference = discard_variable
# 'using' directive preferences
csharp_using_directive_placement = outside_namespace:warning
# New line preferences
csharp_style_allow_blank_line_after_colon_in_constructor_initializer_experimental = false:warning
csharp_style_allow_blank_lines_between_consecutive_braces_experimental = true
csharp_style_allow_embedded_statements_on_same_line_experimental = true
#### C# Formatting Rules ####
# New line preferences
csharp_new_line_before_catch = false
csharp_new_line_before_else = false
csharp_new_line_before_finally = false
csharp_new_line_before_members_in_anonymous_types = true
csharp_new_line_before_members_in_object_initializers = true
csharp_new_line_before_open_brace = none
csharp_new_line_between_query_expression_clauses = true
# Indentation preferences
csharp_indent_block_contents = true
csharp_indent_braces = false
csharp_indent_case_contents = true
csharp_indent_case_contents_when_block = false
csharp_indent_labels = one_less_than_current
csharp_indent_switch_labels = true
# Space preferences
csharp_space_after_cast = true
csharp_space_after_colon_in_inheritance_clause = true
csharp_space_after_comma = true
csharp_space_after_dot = false
csharp_space_after_keywords_in_control_flow_statements = true
csharp_space_after_semicolon_in_for_statement = true
csharp_space_around_binary_operators = before_and_after
csharp_space_around_declaration_statements = false
csharp_space_before_colon_in_inheritance_clause = true
csharp_space_before_comma = false
csharp_space_before_dot = false
csharp_space_before_open_square_brackets = false
csharp_space_before_semicolon_in_for_statement = false
csharp_space_between_empty_square_brackets = false
csharp_space_between_method_call_empty_parameter_list_parentheses = false
csharp_space_between_method_call_name_and_opening_parenthesis = false
csharp_space_between_method_call_parameter_list_parentheses = false
csharp_space_between_method_declaration_empty_parameter_list_parentheses = false
csharp_space_between_method_declaration_name_and_open_parenthesis = false
csharp_space_between_method_declaration_parameter_list_parentheses = false
csharp_space_between_parentheses = false
csharp_space_between_square_brackets = false
# Wrapping preferences
csharp_preserve_single_line_blocks = true
csharp_preserve_single_line_statements = false
#### Naming styles ####
# Naming rules
dotnet_naming_rule.constant_should_be_capslock.severity = warning
dotnet_naming_rule.constant_should_be_capslock.symbols = constant
dotnet_naming_rule.constant_should_be_capslock.style = capslock
dotnet_naming_rule.local_should_be_camel_case.severity = warning
dotnet_naming_rule.local_should_be_camel_case.symbols = local
dotnet_naming_rule.local_should_be_camel_case.style = camel_case
dotnet_naming_rule.interface_should_be_begins_with_i.severity = warning
dotnet_naming_rule.interface_should_be_begins_with_i.symbols = interface
dotnet_naming_rule.interface_should_be_begins_with_i.style = begins_with_i
dotnet_naming_rule.types_should_be_pascal_case.severity = warning
dotnet_naming_rule.types_should_be_pascal_case.symbols = types
dotnet_naming_rule.types_should_be_pascal_case.style = pascal_case
dotnet_naming_rule.non_field_members_should_be_pascal_case.severity = warning
dotnet_naming_rule.non_field_members_should_be_pascal_case.symbols = non_field_members
dotnet_naming_rule.non_field_members_should_be_pascal_case.style = pascal_case
# Symbol specifications
dotnet_naming_symbols.interface.applicable_kinds = interface
dotnet_naming_symbols.interface.applicable_accessibilities = public, internal, private, protected, protected_internal
dotnet_naming_symbols.interface.required_modifiers =
dotnet_naming_symbols.types.applicable_kinds = class, struct, interface, enum
dotnet_naming_symbols.types.applicable_accessibilities = public, internal, private, protected, protected_internal
dotnet_naming_symbols.types.required_modifiers =
dotnet_naming_symbols.non_field_members.applicable_kinds = property, event, method
dotnet_naming_symbols.non_field_members.applicable_accessibilities = public, internal, private, protected, protected_internal
dotnet_naming_symbols.non_field_members.required_modifiers =
dotnet_naming_symbols.constant.applicable_kinds = *
dotnet_naming_symbols.constant.applicable_accessibilities = *
dotnet_naming_symbols.constant.required_modifiers = const
dotnet_naming_symbols.local.applicable_kinds = *
dotnet_naming_symbols.local.applicable_accessibilities = local
dotnet_naming_symbols.local.required_modifiers =
# Naming styles
dotnet_naming_style.pascal_case.required_prefix =
dotnet_naming_style.pascal_case.required_suffix =
dotnet_naming_style.pascal_case.word_separator =
dotnet_naming_style.pascal_case.capitalization = pascal_case
dotnet_naming_style.begins_with_i.required_prefix = I
dotnet_naming_style.begins_with_i.required_suffix =
dotnet_naming_style.begins_with_i.word_separator =
dotnet_naming_style.begins_with_i.capitalization = pascal_case
dotnet_naming_style.capslock.required_prefix =
dotnet_naming_style.capslock.required_suffix =
dotnet_naming_style.capslock.word_separator =
dotnet_naming_style.capslock.capitalization = all_upper
dotnet_naming_style.camel_case.required_prefix =
dotnet_naming_style.camel_case.required_suffix =
dotnet_naming_style.camel_case.word_separator =
dotnet_naming_style.camel_case.capitalization = camel_case
PS: I know using underscores in identifiers is sort of frowned upon, the reason I use them is because I name my constants in capslock, which, I think, is also frowned upon? I do that because I prefer having a clear indication of what's a constant and what isn't.
CodePudding user response：
I'm pretty sure this is a bug with the naming rule code, and I've opened an issue with Roslyn here.
The problem happens when you have a naming rule which applies to your consts (although I suspect the exact type of symbol doesn't matter). The code which checks that a name meets a rule is here. It's fine up to this section:
name = StripCommonPrefixes(name.Substring(Prefix.Length), out var prefix);
if (prefix != string.Empty)
{
// name started with specified prefix, but has at least one additional common prefix
// Example: specified prefix "test_", actual prefix "test_m_"
failureReason = Prefix == string.Empty ?
string.Format(CompilerExtensionsResources.Prefix_0_is_not_expected, prefix) :
string.Format(CompilerExtensionsResources.Prefix_0_does_not_match_expected_prefix_1, prefix, Prefix);
return false;
}
(Prefix_0_is_not_expected is the "Prefix '{0}' is not expected" error message you're seeing, which is how I found this code.)
StripCommonPrefixes looks like this:
public static string StripCommonPrefixes(string name, out string prefix)
{
var index = 0;
while (index 1 < name.Length)
{
switch (char.ToLowerInvariant(name[index]))
{
case 'm':
case 's':
case 't':
if (index 2 < name.Length && name[index 1] == '_')
{
index = 2;
continue;
}
break;
case '_':
index ;
continue;
default:
break;
}
// If we reach this point, the current iteration did not strip any additional characters
break;
}
prefix = name.Substring(0, index);
return name.Substring(index);
}
If it finds that the name starts with m_, s_ or t_ (in any casing) with any number of leading unerscores, it determines that it's a "prefix". Since we didn't configure a prefix, and it found one, we get a warning.
This is why you found the rule only fires with S_ and T_ (you missed M_).
However, I don't see how this code can reliably determine what is a prefix and what isn't given that our name is supposed to contain underscores, which is why I raised it as an issue.
When this code was originally introduced, it just stripped common prefixes from the name. This was changed in Jan 2019, apparently with unintended consequences.
CodePudding user response：
Are the prefixes T_, t_, S_, s_ used for anything specific
Quote the coding conventions manual:
When working with
staticfields that areprivateorinternal, use thes_prefix and for thread static uset_.public class DataService { private static IWorkerQueue s_workerQueue; [ThreadStatic] private static TimeSpan t_timeSpan; }