[swift-dev] Categorization of warnings in Swift

[Michael Gottesman]

> On Jan 12, 2016, at 9:44 AM, Michael Ilseman via swift-dev <swift-dev at swift.org> wrote:
> 
> Hello, I'm interested in enabling finer-grained control over warning/error
> reporting ala Clang. I've started to put in some infrastructure to
> DiagnosticEngine, and now I'm at the point of determining categorization. 
> 
> I'd like some input (and maybe even some bikeshedding!) on the community's
> thoughts and preferences here. Here's my take on the issue:
> 
> When it comes to defining the categorization, I can see a few approaches: 
>  Categorize based on broad language-feature/compiler-area. E.g. "Availability" or “CommandLineArguments”
>  Categorize based on the kind of warning. E.g. "Deprecated" or  “Uninitialized"
>  Categorize based on severity or specificity of warnings. E.g. "Pedantic" or "UnusedValue" or "NullDereference"
> 
> And, of course, I think that preference should be given to how people would
> actively like to use the categories to control warnings. For example, there's
> a handful of warnings that makes less sense in a REPL or rapid experimentation
> environment, such as variable_never_mutated.
> 
> Here's a straw-man proposal of some categorization. Of course, one developer's
> annoying pedantic warning is another's life-saving code-smell detector. I am not
> personally tied to these categorizations at all, I'm just interested in there
> being something simple and basic. Below is a list of every warning in Swift with
> an attempt to put it under a category.
> 
> 
> Deprecated:
>     var_not_allowed_in_pattern
>         "Use of '%select{var|let}0' binding here is deprecated and will be "
>         "removed in a future version of Swift"
>     deprecated_c_style_for_stmt
>         "C-style for statement is deprecated and will be removed in a future "
>         "version of Swift"
>     deprecated_convention_attribute
>         "'@%0' attribute is deprecated; '@convention(%1)' should be used "
>         "instead"
>     availability_deprecated
>         "%0 %select{is|%select{is|was}3}1 deprecated"
>         "%select{| %select{on|in}3 %2%select{| %4}3}1"
>     availability_deprecated_msg
>         "%0 %select{is|%select{is|was}3}1 deprecated"
>         "%select{| %select{on|in}3 %2%select{| %4}3}1: %5"
>     availability_deprecated_rename
>         "%0 %select{is|%select{is|was}3}1 deprecated"
>         "%select{| %select{on|in}3 %2%select{| %4}3}1: renamed to '%5'"
>     parameter_curry_syntax_removed
>         "curried function declaration syntax will be removed in a future "
>         "version of Swift; use a single parameter list"
> 
> 
> Unsupported:
>     warning_parallel_execution_not_supported
>         "parallel execution not supported; falling back to serial execution"
>     unsupported_synthesize_init_variadic
>         "synthesizing a variadic inherited initializer for subclass %0 is "
>         "unsupported"
> 
> 
> Stylistic/Pedantic/Cleanliness:
>     pbd_never_used_stmtcond
>         "value %0 was defined but never used; consider replacing "
>         "with boolean test"
>     pbd_never_used
>         "initialization of %select{variable|immutable value}1 %0 was never used"
>         "; consider replacing with assignment to '_' or removing it"
>     capture_never_used
>         "capture %0 was never used",
>     variable_never_used
>         "%select{variable|immutable value}1 %0 was never used; "
>         "consider replacing with '_' or removing it"
>     variable_never_mutated
>         "%select{variable|parameter}1 %0 was never mutated; "
>         "consider changing to 'let' constant"
>     variable_never_read
>         "%select{variable|parameter}1 %0 was written to, but never read"
>     expression_unused_result
>         "result of call to %0 is unused"
>     expression_unused_init_result
>         "result of initializer is unused", ())
>     expression_unused_result_message
>         "result of call to %0 is unused: %1"
>     expression_unused_result_nonmutating
>         "result of call to non-mutating function %0 is unused; "
>         "use %1 to mutate in-place"
>     expression_unused_optional_try
>         "result of 'try?' is unused"
>     non_trailing_closure_before_default_args
>         "closure parameter prior to parameters with default arguments will "
>         "not be treated as a trailing closure"
>     parameter_extraneous_double_up
>         "extraneous duplicate parameter name; %0 already has an argument "
>         "label"
>     parameter_extraneous_empty_name
>         "extraneous '_' in parameter: %0 has no keyword argument name"
>     escaped_parameter_name
>         "keyword '%0' does not need to be escaped in argument list"
> 
> 
> CodeSmell/StrongStylisticHints:
>     guard_always_succeeds
>         "'guard' condition is always true, body is unreachable"
>     warn_unqualified_access
>         "use of %0 treated as a reference to %1 in %2 %3"
>     var_pattern_didnt_bind_variables
>         "'%0' pattern has no effect; sub-pattern didn't bind any variables"
>     type_inferred_to_undesirable_type
>         "%select{variable|constant}2 %0 inferred to have type %1, "
>         "which may be unexpected"
>     no_throw_in_try
>         "no calls to throwing functions occur within 'try' expression"
>     no_throw_in_do_with_catch
>         "'catch' block is unreachable because no errors are thrown in 'do' block"
>     required_initializer_override_keyword
>         "'override' is implied when overriding a required initializer"
>     if_always_true
>         "'if' condition is always true"
>     while_always_true
>         "'while' condition is always true"
>     warn_protocol_witness_optionality
>         "%select{type|result|parameter|parameters|"
>         "result and parameters}0 of %1 %select{has|has|has|have|have|}0"
>         " different optionality than expected by protocol %2"
>     optional_req_nonobjc_near_match
>         "non- at objc %select{initializer %1|method %1|property %1|subscript}0 "
>         "cannot satisfy optional requirement of @objc protocol %2"
>     override_unnecessary_IUO
>         "overriding %0 parameter of type %1 with implicitly unwrapped optional "
>         "type %2",
>     override_unnecessary_result_IUO
>         "overriding %0 optional result type %1 with implicitly unwrapped "
>         "optional type %2",
>     inject_forced_downcast, sema_tce, none,
>         "treating a forced downcast to %0 as optional will never produce 'nil'"
>     recursive_accessor_reference, tce_sema, none,
>         "attempting to %select{access|modify}1 %0 within its own "
>         "%select{getter|setter}1",
>     store_in_willset, tce_sema, none,
>         "attempting to store to property %0 within its own willSet, which is "
>         "about to be overwritten by the new value",
>     isa_is_always_true
>         "'%0' test is always true",
>     conditional_downcast_coercion
>         "conditional cast from %0 to %1 always succeeds"
>     downcast_to_unrelated, sema_tcc, none,
>         "cast from %0 to unrelated type %1 always fails"
>     forced_downcast_noop
>         "forced cast of %0 to same type has no effect"
>     forced_downcast_coercion
>         "forced cast from %0 to %1 always succeeds; did you mean to use 'as'?"
>     extraneous_default_args_in_call
>         "call to %0 has extraneous arguments that could use defaults"
>     unreachable_code
>         "will never be executed"
>     unreachable_code_after_stmt
>         "code after '%select{return|break|continue|throw}0' will never "
>         "be executed"
>     unreachable_case
>         "%select{case|default}0 will never be executed"
>     switch_on_a_constant
>         "switch condition evaluates to a constant"
>     integer_conversion_overflow_warn
>         "integer overflows when converted from %0 to %1"
>     integer_literal_overflow_warn
>         "integer literal overflows when stored into %0"
>     trailing_closure_excess_newlines
>         "trailing closure is separated from call site by multiple newlines"
>     lex_nul_character, lexing, none
>         "nul character embedded in middle of file"
>     unindented_code_after_return
>         "expression following 'return' is treated as an argument of "
>         "the 'return'"
>     lex_editor_placeholder_in_playground
>         "editor placeholder in source file"
> 
> 
> Attributes:
>     attr_availability_unknown_platform
>         "unknown platform '%0' for attribute '%1'"
>     attr_warn_unused_result_expected_name
>         "expected parameter 'message' or 'mutable_variant'"
>     attr_warn_unused_result_duplicate_parameter
>         "duplicate '%0' parameter; previous value will be ignored"
>     attr_warn_unused_result_unknown_parameter
>         "unknown parameter '%0' in 'warn_unused_result' attribute"
>     attr_migration_id_expected_name
>         "expected parameter 'pattern'"
>     attr_migration_id_unknown_parameter
>         "unknown parameter '%0' in '_migration_id' attribute"
>     attr_migration_id_duplicate_parameter
>         "duplicate '%0' parameter; previous value will be ignored"
>     invalid_swift_name_method
>         "too %select{few|many}0 parameters in swift_name attribute (expected %1; "
>         "got %2)"
> 
> Availability:
>     availability_query_useless_min_deployment
>         "unnecessary check for '%0'; minimum deployment target ensures guard "
>         "will always be true"
>     availability_query_useless_enclosing_scope
>         "unnecessary check for '%0'; enclosing scope ensures guard "
>         "will always be true"
> 
> And the below I'm either struggling to think about how to categorize them
> (perhaps no category at first), or un-familiar with what they're targeting
>     warning_from_clang:
>         "%0"
>     could_not_rewrite_bridging_header, none, none,
>         "failed to serialize bridging header; "
>         "target may not be debuggable outside of its original project"
>     omit_needless_words
>         "%0 could be named %1 [-Womit-needless-words]"
>     unused_compiler_version_component
>         "the second version component is not used for comparison"
>     unknown_build_config
>         "unknown %0 for build configuration '%1'"
>     sema_import_current_module
>         "this file is part of module %0; ignoring import"
>     sema_import_current_module_with_file
>         "file '%0' is part of module %1; ignoring import"
>     access_control_member_more
>         "declaring %select{PRIVATE|an internal|a public}0 %1 for "
>         "%select{a private|an internal|PUBLIC}2 %3"
>     access_control_ext_member_more
>         "declaring %select{PRIVATE|an internal|a public}0 %1 in "
>         "%select{a private|an internal|PUBLIC}2 extension"
>     emit_reference_dependencies_without_primary_file
>         "ignoring -emit-reference-dependencies (requires -primary-file)"
>     warning_no_such_sdk
>         "no such SDK: '%0'"
>     warn_cannot_stat_input
>         "unable to determine when '%0' was last modified: %1"
>     warning_unnecessary_repl_mode
>         "unnecessary option '%0'; this is the default for '%1' "
>         "with no input files"
>     incremental_requires_output_file_map
>         "ignoring -incremental (currently requires an output file map)"
>     incremental_requires_build_record_entry
>         "ignoring -incremental; output file map has no master dependencies "
>         "entry (\"%0\" under \"\")"
> 
> I haven’t gotten to how to expose this to the user, and I’ll defer to the community for suggestions in that area. 

Just an FYI: We have also talked about performance related warnings at the SIL level (that could potentially be a hard error). We do not have any such thing implemented right now, but keep it in mind.

Michael

> 
> 
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