coqPackages.mkCoqDerivation: rely on namePrefix to compute default opam-name

As suggested by Cyril Cohen in https://github.com/NixOS/nixpkgs/pull/134362#discussion_r698379405.

doc/languages-frameworks/coq.section.md

@@ -28,12 +28,12 @@ The recommended way of defining a derivation for a Coq library, is to use the `c
 * `domain` (optional, defaults to `"github.com"`), domains including the strings `"github"` or `"gitlab"` in their names are automatically supported, otherwise, one must change the `fetcher` argument to support them (cf `pkgs/development/coq-modules/heq/default.nix` for an example),
 * `releaseRev` (optional, defaults to `(v: v)`), provides a default mapping from release names to revision hashes/branch names/tags,
 * `displayVersion` (optional), provides a way to alter the computation of `name` from `pname`, by explaining how to display version numbers,
-* `namePrefix` (optional), provides a way to alter the computation of `name` from `pname`, by explaining which dependencies must occur in `name`,
+* `namePrefix` (optional, defaults to `[ "coq" ]`), provides a way to alter the computation of `name` from `pname`, by explaining which dependencies must occur in `name`,
 * `extraBuildInputs` (optional), by default `buildInputs` just contains `coq`, this allows to add more build inputs,
 * `mlPlugin` (optional, defaults to `false`). Some extensions (plugins) might require OCaml and sometimes other OCaml packages. Standard dependencies can be added by setting the current option to `true`. For a finer grain control, the `coq.ocamlPackages` attribute can be used in `extraBuildInputs` to depend on the same package set Coq was built against.
 * `useDune2ifVersion` (optional, default to `(x: false)` uses Dune2 to build the package if the provided predicate evaluates to true on the version, e.g. `useDune2if = versions.isGe "1.1"`  will use dune if the version of the package is greater or equal to `"1.1"`,
 * `useDune2` (optional, defaults to `false`) uses Dune2 to build the package if set to true, the presence of this attribute overrides the behavior of the previous one.
-* `opam-name` (optional, defaults to `coq-` followed by the value of `pname`), name of the Dune package to build.
+* `opam-name` (optional, defaults to concatenating with a dash separator the components of `namePrefix` and `pname`), name of the Dune package to build.
 * `enableParallelBuilding` (optional, defaults to `true`), since it is activated by default, we provide a way to disable it.
 * `extraInstallFlags` (optional), allows to extend `installFlags` which initializes the variable `COQMF_COQLIB` so as to install in the proper subdirectory. Indeed Coq libraries should be installed in `$(out)/lib/coq/${coq.coq-version}/user-contrib/`. Such directories are automatically added to the `$COQPATH` environment variable by the hook defined in the Coq derivation.
 * `setCOQBIN` (optional, defaults to `true`), by default, the environment variable `$COQBIN` is set to the current Coq's binary, but one can disable this behavior by setting it to `false`,

pkgs/build-support/coq/default.nix

@@ -16,7 +16,7 @@ in
   displayVersion ? {},
   release ? {},
   extraBuildInputs ? [],
-  namePrefix ? [],
+  namePrefix ? [ "coq" ],
   enableParallelBuilding ? true,
   extraInstallFlags ? [],
   setCOQBIN ? true,
@@ -27,7 +27,7 @@ in
   dropDerivationAttrs ? [],
   useDune2ifVersion ? (x: false),
   useDune2 ? false,
-  opam-name ? "coq-${pname}",
+  opam-name ? (concatStringsSep "-" (namePrefix ++ [ pname ])),
   ...
 }@args:
 let
@@ -44,7 +44,6 @@ let
       location = { inherit domain owner repo; };
     } // optionalAttrs (args?fetcher) {inherit fetcher;});
   fetched = fetch (if !isNull version then version else defaultVersion);
-  namePrefix = args.namePrefix or [ "coq" ];
   display-pkg = n: sep: v:
     let d = displayVersion.${n} or (if sep == "" then ".." else true); in
     n + optionalString (v != "" && v != null) (switch d [

pkgs/development/coq-modules/multinomials/default.nix

@@ -4,7 +4,6 @@ with lib; mkCoqDerivation {
 
   namePrefix = [ "coq" "mathcomp" ];
   pname = "multinomials";
-  opam-name = "coq-mathcomp-multinomials";
 
   owner = "math-comp";