lib, treewide: introduce repoRevToName, use it in most fetch* functions

This patch adds `lib.repoRevToName` function that generalizes away most of the
code used for derivation name generation by `fetch*` functions (`fetchzip`,
`fetchFromGitHub`, etc, except those which are delayed until latter commits
for mass-rebuild reasons).

It's first argument controls how the resulting name will look (see below).

Since `lib` has no equivalent of Nixpkgs' `config`, this patch adds
`config.fetchedSourceNameDefault` option to Nixpkgs and then re-exposes
`lib.repoRevToName config.fetchedSourceNameDefault` expression as
`pkgs.repoRevToNameMaybe` which is then used in `fetch*` derivations.

The result is that different values of `config.fetchedSourceNameDefault` now
control how the `src` derivations produced by `fetch*` functions are to be
named, e.g.:

- `fetchedSourceNameDefault = "source"` (the default):

  ```
  $ nix-instantiate -A fuse.src
  /nix/store/<hash>-source.drv
  ```

- `fetchedSourceNameDefault = "versioned"`:

  ```
  $ nix-instantiate -A fuse.src
  /nix/store/<hash>-libfuse-2.9.9-source.drv
  ```

- `fetchedSourceNameDefault = "full"`:

  ```
  $ nix-instantiate -A fuse.src
  /nix/store/<hash>-libfuse-2.9.9-github-source.drv
  ```

See the documentation of `config.fetchedSourceNameDefault` for more info.

lib/sources.nix

@@ -3,7 +3,7 @@
 
 # Tested in lib/tests/sources.sh
 let
-  inherit (builtins)
+  inherit (lib.strings)
     match
     split
     storeDir
@@ -403,6 +403,101 @@ let
       };
     };
 
+  # urlToName : (URL | Path | String) -> String
+  #
+  # Transform a URL (or path, or string) into a clean package name.
+  urlToName =
+    url:
+    let
+      inherit (lib.strings) stringLength;
+      base = baseNameOf (lib.removeSuffix "/" (lib.last (lib.splitString ":" (toString url))));
+      # chop away one git or archive-related extension
+      removeExt =
+        name:
+        let
+          matchExt = match "(.*)\\.(git|tar|zip|gz|tgz|bz|tbz|bz2|tbz2|lzma|txz|xz|zstd)$" name;
+        in
+        if matchExt != null then lib.head matchExt else name;
+      # apply function f to string x while the result shrinks
+      shrink =
+        f: x:
+        let
+          v = f x;
+        in
+        if stringLength v < stringLength x then shrink f v else x;
+    in
+    shrink removeExt base;
+
+  # shortRev : (String | Integer) -> String
+  #
+  # Given a package revision (like "refs/tags/v12.0"), produce a short revision ("12.0").
+  shortRev =
+    rev:
+    let
+      baseRev = baseNameOf (toString rev);
+      matchHash = match "[a-f0-9]+" baseRev;
+      matchVer = match "([A-Za-z]+[-_. ]?)*(v)?([0-9.]+.*)" baseRev;
+    in
+    if matchHash != null then
+      builtins.substring 0 7 baseRev
+    else if matchVer != null then
+      lib.last matchVer
+    else
+      baseRev;
+
+  # revOrTag : String -> String -> String
+  #
+  # Turn git `rev` and `tag` pair into a revision usable in `repoRevToName*`.
+  revOrTag =
+    rev: tag:
+    if tag != null then
+      tag
+    else if rev != null then
+      rev
+    else
+      "HEAD";
+
+  # repoRevToNameFull : (URL | Path | String) -> (String | Integer | null) -> (String | null) -> String
+  #
+  # See `repoRevToName` below.
+  repoRevToNameFull =
+    repo_: rev_: suffix_:
+    let
+      repo = urlToName repo_;
+      rev = if rev_ != null then "-${shortRev rev_}" else "";
+      suffix = if suffix_ != null then "-${suffix_}" else "";
+    in
+    "${repo}${rev}${suffix}-source";
+
+  # repoRevToName : String -> (URL | Path | String) -> (String | Integer | null) -> String -> String
+  #
+  # Produce derivation.name attribute for a given repository URL/path/name and (optionally) its revision/version tag.
+  #
+  # This is used by fetch(zip|git|FromGitHub|hg|svn|etc) to generate discoverable
+  # /nix/store paths.
+  #
+  # This uses a different implementation depending on the `pretty` argument:
+  #  "source" -> name everything as "source"
+  #  "versioned" -> name everything as "${repo}-${rev}-source"
+  #  "full" -> name everything as "${repo}-${rev}-${fetcher}-source"
+  repoRevToName =
+    kind:
+    # match on `kind` first to minimize the thunk
+    if kind == "source" then
+      (
+        repo: rev: suffix:
+        "source"
+      )
+    else if kind == "versioned" then
+      (
+        repo: rev: suffix:
+        repoRevToNameFull repo rev null
+      )
+    else if kind == "full" then
+      repoRevToNameFull
+    else
+      throw "repoRevToName: invalid kind";
+
 in
 {
 
@@ -431,6 +526,11 @@ in
     pathHasContext
     canCleanSource
 
+    urlToName
+    shortRev
+    revOrTag
+    repoRevToName
+
     sourceByRegex
     sourceFilesBySuffices