texlive: make packages fixed-output derivations

This reverts a part of the changes made in #40826.
Fixed-output derivations save time and space on rebuilds.

pkgs/tools/typesetting/tex/texlive/default.nix

@@ -29,6 +29,7 @@
 { stdenv, lib, fetchurl, runCommand, writeText, buildEnv
 , callPackage, ghostscriptX, harfbuzz, poppler_min
 , makeWrapper, python, ruby, perl
+, useFixedHashes ? true
 , recurseIntoAttrs
 }:
 let
@@ -41,6 +42,10 @@ let
     };
   };
 
+  # map: name -> fixed-output hash
+  # sha1 in base32 was chosen as a compromise between security and length
+  fixedHashes = lib.optionalAttrs useFixedHashes (import ./fixedHashes.nix);
+
   # function for creating a working environment from a set of TL packages
   combine = import ./combine.nix {
     inherit bin combinePkgs buildEnv fastUnique lib makeWrapper writeText
@@ -116,6 +121,7 @@ let
       # the basename used by upstream (without ".tar.xz" suffix)
       urlName = pname + lib.optionalString (tlType != "run") ".${tlType}";
       tlName = urlName + "-${version}";
+      fixedHash = fixedHashes.${tlName} or null; # be graceful about missing hashes
 
       urls = args.urls or (if args ? url then [ args.url ] else
               map (up: "${up}/${urlName}.tar.xz") urlPrefixes
@@ -155,11 +161,30 @@ let
           -C "$out" --anchored --exclude=tlpkg --keep-old-files
       '' + postUnpack;
 
-    in runCommand "texlive-${tlName}" {
+    in if sha512 == "" then
-        # lots of derivations, not meant to be cached
+      # hash stripped from pkgs.nix to save space -> fetch&unpack in a single step
+      fetchurl {
+        inherit urls;
+        sha1 = if fixedHash == null then throw "TeX Live package ${tlName} is missing hash!"
+          else fixedHash;
+        name = tlName;
+        recursiveHash = true;
+        downloadToTemp = true;
+        postFetch = ''mkdir "$out";'' + unpackCmd "$downloadedFile";
+        # TODO: perhaps override preferHashedMirrors and allowSubstitutes
+     }
+        // passthru
+
+    else runCommand "texlive-${tlName}"
+      ( { # lots of derivations, not meant to be cached
           preferLocalBuild = true; allowSubstitutes = false;
           inherit passthru;
+        } // lib.optionalAttrs (fixedHash != null) {
+          outputHash = fixedHash;
+          outputHashAlgo = "sha1";
+          outputHashMode = "recursive";
         }
+      )
       ( ''
           mkdir "$out"
         '' + unpackCmd "'${src}'"

pkgs/tools/typesetting/tex/texlive/fixHashes.sh

@@ -0,0 +1,10 @@
+#!/bin/sh
+
+echo "{"
+grep -v -F '.bin-' | while read path; do
+    hash=`nix-hash --type sha1 --base32 "$path"`
+    echo -n "$path" | sed -E 's/[^-]*-texlive-(.*)/"\1"/'
+    echo "=\"$hash\";"
+done
+echo "}"
+