Create nix derivation add command

Also refine `nix derivation show`'s docs very slightly.

tests/ca/derivation-json.sh

@@ -0,0 +1,26 @@
+source common.sh
+
+export NIX_TESTS_CA_BY_DEFAULT=1
+
+drvPath=$(nix-instantiate ../simple.nix)
+
+nix derivation show $drvPath | jq .[] > $TEST_HOME/simple.json
+
+drvPath2=$(nix derivation add < $TEST_HOME/simple.json)
+
+[[ "$drvPath" = "$drvPath2" ]]
+
+# Content-addressed derivations can be renamed.
+jq '.name = "foo"' < $TEST_HOME/simple.json > $TEST_HOME/foo.json
+drvPath3=$(nix derivation add --dry-run < $TEST_HOME/foo.json)
+# With --dry-run nothing is actually written
+[[ ! -e "$drvPath3" ]]
+
+# Without --dry-run it is actually written
+drvPath4=$(nix derivation add < $TEST_HOME/foo.json)
+[[ "$drvPath4" = "$drvPath3" ]]
+[[ -e "$drvPath3" ]]
+
+# The modified derivation read back as JSON matches
+nix derivation show $drvPath3 | jq .[] > $TEST_HOME/foo-read.json
+diff $TEST_HOME/foo.json $TEST_HOME/foo-read.json

tests/derivation-json.sh

@@ -0,0 +1,12 @@
+source common.sh
+
+drvPath=$(nix-instantiate simple.nix)
+
+nix derivation show $drvPath | jq .[] > $TEST_HOME/simple.json
+
+drvPath2=$(nix derivation add < $TEST_HOME/simple.json)
+
+[[ "$drvPath" = "$drvPath2" ]]
+
+# Input addressed derivations cannot be renamed.
+jq '.name = "foo"' < $TEST_HOME/simple.json | expectStderr 1 nix derivation add | grepQuiet "has incorrect output"

tests/local.mk

@@ -102,6 +102,8 @@ nix_tests = \
   eval-store.sh \
   why-depends.sh \
   ca/why-depends.sh \
+  derivation-json.sh \
+  ca/derivation-json.sh \
   import-derivation.sh \
   ca/import-derivation.sh \
   nix_path.sh \