Warnings(3)

💅 Warnings — Warning definitions 💅

okay so bestie, this is the Warnings module from the OCaml library, manual page Warnings(3) — no cap. It’s literally the page for warning definitions, and the whole vibe is “here are all the warning types and the little functions that go with them.” 🫶

📛 NAME 📛

Warnings — Warning definitions. That’s the tea. 🍓

🧩 Module 🧩

The module is Warnings. That’s it, that’s the module. 💅

📚 Documentation 📚

Here’s the module signature wrapper, bestie:

Module Warnings
 : sig end

🌸 Warning definitions 🌸

🚨 Warning: this module is unstable and part of Compiler_libs .

Lowkey important, highkey still iconic. Now onto the types. ✨

type loc — the location record, with all three fields:

type loc = {
 loc_start : Lexing.position ;
 loc_end : Lexing.position ;
 loc_ghost : bool ;
 }

• val ghost_loc_in_file : string -> loc — returns an empty ghost range located in a given file. 👻

type field_usage_warning — the field-usage warning variants:

type field_usage_warning =
 | Unused
 | Not_read
 | Not_mutated

type constructor_usage_warning — the constructor-usage warning variants:

type constructor_usage_warning =
 | Unused
 | Not_constructed
 | Only_exported_private

type type_declaration_usage_warning — the type-declaration usage warning variants:

type type_declaration_usage_warning =
 | Declaration
 | Alias

type t — okay bestie, this is the big one. The way this type ate and left no crumbs. All the warning constructors, periodt:

type t =
 | Comment_start
 | Comment_not_end
 | Fragile_match of string
 | Ignored_partial_application
 | Labels_omitted of string list
 | Method_override of string list
 | Partial_match of Format_doc.t
 | Missing_record_field_pattern of string
 | Non_unit_statement
 | Redundant_case
 | Redundant_subpat
 | Instance_variable_override of string list
 | Illegal_backslash
 | Implicit_public_methods of string list
 | Unerasable_optional_argument
 | Undeclared_virtual_method of string
 | Not_principal of Format_doc.t
 | Non_principal_labels of string
 | Ignored_extra_argument
 | Nonreturning_statement
 | Preprocessor of string
 | Useless_record_with
 | Bad_module_name of string
 | All_clauses_guarded
 | Unused_var of string
 | Unused_var_strict of string
 | Wildcard_arg_to_constant_constr
 | Eol_in_string
 | Duplicate_definitions of string * string * string * string
 | Unused_value_declaration of string
 | Unused_open of string
 | Unused_type_declaration of string * type_declaration_usage_warning
 | Unused_for_index of string
 | Unused_ancestor of string
 | Unused_constructor of string * constructor_usage_warning
 | Unused_extension of string * bool * constructor_usage_warning
 | Unused_rec_flag
 | Name_out_of_scope of string * string list * bool
 | Ambiguous_name of string list * string list * bool * string
 | Disambiguated_name of string
 | Nonoptional_label of string
 | Open_shadow_identifier of string * string
 | Open_shadow_label_constructor of string * string
 | Bad_env_variable of string * string
 | Attribute_payload of string * string
 | Eliminated_optional_arguments of string list
 | No_cmi_file of string * string option
 | Unexpected_docstring of bool
 | Wrong_tailcall_expectation of bool
 | Fragile_literal_pattern
 | Misplaced_attribute of string
 | Duplicated_attribute of string
 | Inlining_impossible of string
 | Unreachable_case
 | Ambiguous_var_in_pattern_guard of string list
 | No_cmx_file of string
 | Flambda_assignment_to_non_mutable_value
 | Unused_module of string
 | Unboxable_type_in_prim_decl of string
 | Constraint_on_gadt
 | Erroneous_printed_signature of string
 | Unsafe_array_syntax_without_parsing
 | Redefining_unit of string
 | Unused_open_bang of string
 | Unused_functor_parameter of string
 | Match_on_mutable_state_prevent_uncurry
 | Unused_field of string * field_usage_warning
 | Missing_mli
 | Unused_tmc_attribute
 | Tmc_breaks_tailcall
 | Generative_application_expects_unit
 | Degraded_to_partial_match
 | Unnecessarily_partial_tuple_pattern

type alert — the alert record, with its four fields:

type alert = {
 kind : string ;
 message : string ;
 def : loc ;
 use : loc ;
 }

• val parse_options : bool -> string -> alert option — signature only, no extra notes here. 🎀
• val parse_alert_option : string -> unit — disables/enables alerts based on the parameter to the -alert command-line option. Raises Arg.Bad if the string is not a valid specification. 🚨
• val without_warnings : (unit -> 'a) -> 'a — runs the thunk with all warnings and alerts disabled. 😌
• val is_active : t -> bool — signature only. ✨
• val is_error : t -> bool — signature only. ✨
• val defaults_w : string — signature only. 🌈
• val defaults_warn_error : string — signature only. 🌈

type reporting_information — the reporting-info record:

type reporting_information = {
 id : string ;
 message : Format_doc.t ;
 is_error : bool ;
 sub_locs : (loc * Format_doc.t) list ;
 }

• val report : t -> [ Active of reporting_information | Inactive ] — signature only. 💖
• val report_alert : alert -> [ Active of reporting_information | Inactive ] — signature only. 💖

exception Errors — yes, an exception literally named Errors. 😭

• val check_fatal : unit -> unit — signature only. 🔥
• val reset_fatal : unit -> unit — signature only. 🔥
• val help_warnings : unit -> unit — signature only. 🫶

type state — signature only, no fields listed.

• val backup : unit -> state — signature only. 🎀
• val restore : state -> unit — signature only. 🎀
• val with_state : state -> (unit -> 'a) -> 'a — signature only. 🎀
• val mk_lazy : (unit -> 'a) -> 'a Lazy.t — like Lazy.of_fun, but the function is applied with the warning/alert settings at the time mk_lazy is called. 🦋

type description — the description record:

type description = {
 number : int ;
 names : string list ;
 description : string ;
 since : Sys.ocaml_release_info option ;
 }

• val descriptions : description list — signature only. 👑

✨ footer vibe check: source/version OCamldoc, date 2026-06-22, manual page Warnings(3) — bye bestie, mwah 💋💖