Use ^ not ! in indexed store derivations installable syntax

Match the other syntax that was recently added

src/libcmd/installables.cc

@@ -799,11 +799,12 @@ std::vector<std::shared_ptr<Installable>> SourceExprCommand::parseInstallables(
         for (auto & s : ss) {
             std::exception_ptr ex;
 
-            if (s.rfind('!') != std::string::npos) {
+            auto found = s.rfind('^');
+            if (found != std::string::npos) {
                 try {
                     result.push_back(std::make_shared<InstallableIndexedStorePath>(
                         store,
-                        DerivedPath::Built::parse(*store, s)));
+                        DerivedPath::Built::parse(*store, s.substr(0, found), s.substr(found + 1))));
                     settings.requireExperimentalFeature(Xp::ComputedDerivations);
                     continue;
                 } catch (BadStorePath &) {
@@ -813,7 +814,8 @@ std::vector<std::shared_ptr<Installable>> SourceExprCommand::parseInstallables(
                 }
             }
 
-            if (s.find('/') != std::string::npos) {
+            found = s.find('/');
+            if (found != std::string::npos) {
                 try {
                     result.push_back(std::make_shared<InstallableStorePath>(store, store->followLinksToStorePath(s)));
                     continue;

src/libstore/derived-path.cc

@@ -93,12 +93,9 @@ DerivedPath::Opaque DerivedPath::Opaque::parse(const Store & store, std::string_
     return {store.parseStorePath(s)};
 }
 
-DerivedPath::Built DerivedPath::Built::parse(const Store & store, std::string_view s)
+DerivedPath::Built DerivedPath::Built::parse(const Store & store, std::string_view drvS, std::string_view outputsS)
 {
-    size_t n = s.find("!");
+    auto drvPath = store.parseStorePath(drvS);
-    assert(n != s.npos);
-    auto drvPath = store.parseStorePath(s.substr(0, n));
-    auto outputsS = s.substr(n + 1);
     std::set<std::string> outputs;
     if (outputsS != "*")
         outputs = tokenizeString<std::set<std::string>>(outputsS, ",");
@@ -107,10 +104,10 @@ DerivedPath::Built DerivedPath::Built::parse(const Store & store, std::string_vi
 
 DerivedPath DerivedPath::parse(const Store & store, std::string_view s)
 {
-    size_t n = s.find("!");
+    size_t n = s.rfind("!");
     return n == s.npos
         ? (DerivedPath) DerivedPath::Opaque::parse(store, s)
-        : (DerivedPath) DerivedPath::Built::parse(store, s);
+        : (DerivedPath) DerivedPath::Built::parse(store, s.substr(0, n), s.substr(n + 1));
 }
 
 RealisedPath::Set BuiltPath::toRealisedPaths(Store & store) const

src/libstore/derived-path.hh

@@ -47,7 +47,7 @@ struct DerivedPathBuilt {
     std::set<std::string> outputs;
 
     std::string to_string(const Store & store) const;
-    static DerivedPathBuilt parse(const Store & store, std::string_view);
+    static DerivedPathBuilt parse(const Store & store, std::string_view, std::string_view);
     nlohmann::json toJSON(ref<Store> store) const;
 
     bool operator < (const DerivedPathBuilt & b) const

src/nix/nix.md

@@ -130,7 +130,7 @@ the Nix store. Here are the recognised types of installables:
   If you want to operate on the store derivation itself, pass the
   `--derivation` flag.
 
-* **Indexed store derivations**: `/nix/store/p7gp6lxdg32h4ka1q398wd9r2zkbbz2v-hello-2.10.drv!out`
+* **Indexed store derivations**: `/nix/store/p7gp6lxdg32h4ka1q398wd9r2zkbbz2v-hello-2.10.drv^out`
 
   *(Experimental, part of by the `computed-derivations` experimental feature.)*
 

tests/build-explicit-output.sh

@@ -4,11 +4,11 @@ enableFeatures "computed-derivations"
 restartDaemon
 
 drv=$(nix eval -f multiple-outputs.nix --raw a.drvPath)
-if nix build "$drv!not-an-output" --json; then
+if nix build "$drv^not-an-output" --json; then
     fail "'not-an-output' should fail to build"
 fi
 
-nix build "$drv!first" --json | jq --exit-status '
+nix build "$drv^first" --json | jq --exit-status '
   (.[0] |
     (.drvPath | match(".*multiple-outputs-a.drv")) and
     (.outputs |