Writing Coq libraries and plugins¶
This section presents the part of the Coq language that is useful only to library and plugin authors. A tutorial for writing Coq plugins is available in the Coq repository in doc/plugin_tutorial.
Deprecating library objects, tactics or library files¶
You may use the following attribute to deprecate a notation,
tactic, definition, axiom, theorem or file. When renaming a definition or theorem, you can introduce a
deprecated compatibility alias using Notation (abbreviation)
(see the example below).
- Attribute deprecated ( since = string ,? note = string ,? use = qualid? )¶
At least one of
since
ornote
must be present. If both are present, either one may appear first and they must be separated by a comma. If they are present, they will be used in the warning message, andsince
will also be used in the warning name and categories. Spaces insidesince
are changed to hyphens.This attribute is supported by the following commands:
Ltac
,Tactic Notation
,Notation
,Infix
,Ltac2
,Ltac2 Notation
,Ltac2 external
,Definition
,Theorem
, and similar commands. To attach it to a compiled library file, useAttributes
.The
use
attribute can be used for commands such asDefinition
,Theorem
, andNotation @ident
. Its value must refer to an existing constant of abbreviation and is printed as part of the warning message as well as used by LSP based user interfaces as a quick fix.It can trigger the following warnings:
- Warning Library File qualid is deprecated since stringsince. stringnote. Use qualiduse instead.¶
- Warning Library File (transitively required) qualid is deprecated since stringsince. stringnote. Use qualiduse instead.¶
- Warning Ltac2 alias qualid is deprecated since stringsince. stringnote.¶
- Warning Ltac2 definition qualid is deprecated since stringsince. stringnote.¶
- Warning Ltac2 notation ltac2_scope+ is deprecated since stringsince. stringnote.¶
- Warning Ltac2 constructor qualid is deprecated since stringsince. stringnote.¶
- Warning Notation string is deprecated since stringsince. stringnote. Use qualiduse instead.¶
- Warning Tactic qualid is deprecated since stringsince. stringnote.¶
- Warning Tactic Notation qualid is deprecated since stringsince. stringnote.¶
qualid
orstring
is the notation,stringsince
is the version number,stringnote
is the note (usually explains the replacement).Explicitly
Require
ing a file that has been deprecated, using theAttributes
command, triggers aLibrary File
deprecation warning. Requiring a deprecated file, even indirectly through a chain ofRequire
s, will produce aLibrary File (transitively required)
deprecation warning if theWarnings
option "deprecated-transitive-library-file" is set (it is "-deprecated-transitive-library-file" by default, silencing the warning).
Note
Coq and its standard library follow this deprecation policy:
it should always be possible for a project written in Coq to be compatible with two successive major versions,
features must be deprecated in one major version before removal,
Coq developers should provide an estimate of the required effort to fix a project with respect to a given change,
breaking changes should be clearly documented in the public release notes, along with recommendations on how to fix a project if it breaks.
See [Zim19], Section 3.6.3, for more details.
Triggering warning for library objects or library files¶
You may use the following attribute to trigger a warning on a notation, definition, axiom, theorem or file.
- Attribute warn ( note = string , cats = string? )¶
The
note
field will be used as the warning message, andcats
is a comma separated list of categories to be used in the warning name and categories. Leading and trailing spaces in each category are trimmed, whereas internal spaces are changed to hyphens. If bothnote
andcats
are present, either one may appear first and they must be separated by a comma.This attribute is supported by the following commands:
Notation
,Infix
,Definition
,Theorem
, and similar commands. To attach it to a compiled library file, useAttributes
.It can trigger the following warning:
- Warning stringnote¶
stringnote
is the note. It's common practice to start it with a capital and end it with a period.Explicitly
Require
ing a file that has a warn message set using theAttributes
command, triggers awarn-library-file
warning. Requiring such a file, even indirectly through a chain ofRequire
s, will produce awarn-transitive-library-file
warning if theWarnings
option "warn-transitive-library-file" is set (it is "-warn-transitive-library-file" by default, silencing the warning).
Example: Deprecating a tactic.
- #[deprecated(since="mylib 0.9", note="Use idtac instead.")] Ltac foo := idtac.
- foo is defined
- Goal True.
- 1 goal ============================ True
- Proof.
- now foo.
- Toplevel input, characters 4-7: > now foo. > ^^^ Warning: Tactic foo is deprecated since mylib 0.9. Use idtac instead. [deprecated-tactic-since-mylib-0.9,deprecated-since-mylib-0.9,deprecated-tactic,deprecated,default] No more goals.
Example: Introducing a compatibility alias
Let's say your library initially contained:
- Definition foo x := S x.
- foo is defined
and you want to rename foo
into bar
, but you want to avoid breaking
your users' code without advanced notice. To do so, replace the previous
code by the following:
- Definition bar x := S x.
- bar is defined
- #[deprecated(since="mylib 1.2", note="Use bar instead.")] Notation foo := bar (only parsing).
Then, the following code still works, but emits a warning:
- Check (foo 0).
- Toplevel input, characters 7-10: > Check (foo 0). > ^^^ Warning: Notation foo is deprecated since mylib 1.2. Use bar instead. [deprecated-syntactic-definition-since-mylib-1.2,deprecated-since-mylib-1.2,deprecated-syntactic-definition,deprecated,default] bar 0 : nat