fetchpatch: support hunks option (#450207)

doc/build-helpers/fetchers.chapter.md

@@ -699,6 +699,9 @@ MSCREATE.DIR  PINBALL.DOC  PINBALL.MID	Sounds	     WAVEMIX.INF
 - `extraPrefix`: Prefix pathnames by this string.
 - `excludes`: Exclude files matching these patterns (applies after the above arguments).
 - `includes`: Include only files matching these patterns (applies after the above arguments).
+- `hunks`: Choose the specified hunks from each file (applies after the above arguments).
+  Note that you can specify a list of numbers or ranges of numbers
+  (for example, `[ 1 2 3 4 ]`, `[ "1-4" ]`, `[ "-4" ]`, or `[ "1-" ]` would all be the same effective range in a patch applying 4 hunks to a single file).
 - `revert`: Revert the patch.
 
 Note that because the checksum is computed after applying these effects, using or modifying these arguments will have no effect unless the `hash` argument is changed as well.

pkgs/build-support/fetchpatch/default.nix

@@ -17,6 +17,7 @@
   extraPrefix ? null,
   excludes ? [ ],
   includes ? [ ],
+  hunks ? [ ],
   revert ? false,
   postFetch ? "",
   nativeBuildInputs ? [ ],
@@ -90,6 +91,10 @@ lib.throwIfNot (excludes == [ ] || includes == [ ])
           -p1 \
           ${toString (map (x: "-x ${lib.escapeShellArg x}") excludes)} \
           ${toString (map (x: "-i ${lib.escapeShellArg x}") includes)} \
+          ${
+            lib.optionalString (hunks != [ ])
+              "-# ${lib.escapeShellArg (lib.concatMapStringsSep "," toString hunks)}"
+          } \
           "$tmpfile" > "$out"
 
         if [ ! -s "$out" ]; then
@@ -113,6 +118,7 @@ lib.throwIfNot (excludes == [ ] || includes == [ ])
       "extraPrefix"
       "excludes"
       "includes"
+      "hunks"
       "revert"
       "postFetch"
       "nativeBuildInputs"

pkgs/build-support/fetchpatch/tests.nix

@@ -24,18 +24,34 @@ in
         "sha256-KlmIbixcds6GyKYt1fx5BxDIrU7msrgDdYo9Va/KJR4=";
   };
 
+  hunks = testers.invalidateFetcherByDrvHash fetchpatch {
+    url = "https://github.com/openssh/openssh-portable/commit/35d5917652106aede47621bb3f64044604164043.patch";
+    stripLen = 1;
+    hunks = [
+      2
+      3
+      4
+      5
+      6
+      7
+    ];
+    sha256 =
+      if isFetchpatch2 then
+        "sha256-SXJALY4zC4y/ZV7uVglf+XB5cpC5tS4M8QDGlFRmcFM="
+      else
+        "sha256-MV7uGgA1ESMR7W6H5FjAIxKcpySdQjWB+L2zaHjd96M=";
+  };
+
   full = testers.invalidateFetcherByDrvHash fetchpatch {
     url = "https://github.com/boostorg/math/commit/7d482f6ebc356e6ec455ccb5f51a23971bf6ce5b.patch";
     relative = "test";
     stripLen = 1;
     extraPrefix = "foo/bar/";
     excludes = [ "foo/bar/bernoulli_no_atomic_mp.cpp" ];
+    # Should result in no change.
+    hunks = [ "1-" ];
     revert = true;
-    sha256 =
-      if isFetchpatch2 then
-        "sha256-+UKmEbr2rIAweCav/hR/7d4ZrYV84ht/domTrHtm8sM="
-      else
-        "sha256-+UKmEbr2rIAweCav/hR/7d4ZrYV84ht/domTrHtm8sM=";
+    sha256 = "sha256-+UKmEbr2rIAweCav/hR/7d4ZrYV84ht/domTrHtm8sM=";
   };
 
   decode = testers.invalidateFetcherByDrvHash fetchpatch {