Add the submodule info to flake fingerprint

This allows changes to dirty submodules to propagate correctly and
trigger a re-eval as one would expect. This previously only worked with
`__contentAddressed = true;`.

src/libexpr/flake/flake.cc

@@ -727,9 +727,10 @@ Fingerprint LockedFlake::getFingerprint() const
     // and we haven't changed it, then it's sufficient to use
     // flake.sourceInfo.storePath for the fingerprint.
     return hashString(htSHA256,
-        fmt("%s;%s;%d;%d;%s",
+        fmt("%s;%s;%s;%d;%d;%s",
             flake.sourceInfo->storePath.to_string(),
             flake.lockedRef.subdir,
+            flake.lockedRef.input.getModules().value_or(""),
             flake.lockedRef.input.getRevCount().value_or(0),
             flake.lockedRef.input.getLastModified().value_or(0),
             lockFile));

src/libfetchers/fetchers.cc

@@ -257,6 +257,13 @@ std::optional<time_t> Input::getLastModified() const
     return {};
 }
 
+std::optional<std::string> Input::getModules() const
+{
+    if (auto s = maybeGetStrAttr(attrs, "modules"))
+        return *s;
+    return {};
+}
+
 ParsedURL InputScheme::toURL(const Input & input)
 {
     throw Error("don't know how to convert input '%s' to a URL", attrsToJSON(input.attrs));

src/libfetchers/fetchers.hh

@@ -95,6 +95,7 @@ public:
     std::optional<Hash> getRev() const;
     std::optional<uint64_t> getRevCount() const;
     std::optional<time_t> getLastModified() const;
+    std::optional<std::string> getModules() const;
 };