1 files changed, 156 insertions, 0 deletions
diff --git a/home-manager/modules/lib/gvariant.nix b/home-manager/modules/lib/gvariant.nix
new file mode 100644
index 00000000000..92aa7d98371
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+++ b/home-manager/modules/lib/gvariant.nix
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+# A partial and basic implementation of GVariant formatted strings.
+#
+# Note, this API is not considered fully stable and it might therefore
+# change in backwards incompatible ways without prior notice.
+
+{ lib }:
+
+with lib;
+
+let
+
+  mkPrimitive = t: v: {
+    _type = "gvariant";
+    type = t;
+    value = v;
+    __toString = self: "@${self.type} ${toString self.value}";
+  };
+
+  type = {
+    arrayOf = t: "a${t}";
+    maybeOf = t: "m${t}";
+    tupleOf = ts: "(${concatStrings ts})";
+    string = "s";
+    boolean = "b";
+    uchar = "y";
+    int16 = "n";
+    uint16 = "q";
+    int32 = "i";
+    uint32 = "u";
+    int64 = "x";
+    uint64 = "t";
+    double = "d";
+  };
+
+  # Returns the GVariant type of a given Nix value. If no type can be
+  # found for the value then the empty string is returned.
+  typeOf = v:
+    with type;
+    if builtins.isBool v then
+      boolean
+    else if builtins.isInt v then
+      int32
+    else if builtins.isFloat v then
+      double
+    else if builtins.isString v then
+      string
+    else if builtins.isList v then
+      let elemType = elemTypeOf v;
+      in if elemType == "" then "" else arrayOf elemType
+    else if builtins.isAttrs v && v ? type then
+      v.type
+    else
+      "";
+
+  elemTypeOf = vs:
+    if builtins.isList vs then
+      if vs == [ ] then "" else typeOf (head vs)
+    else
+      "";
+
+  mkMaybe = elemType: elem:
+    mkPrimitive (type.maybeOf elemType) elem // {
+      __toString = self:
+        if self.value == null then
+          "@${self.type} nothing"
+        else
+          "just ${toString self.value}";
+    };
+
+in rec {
+
+  inherit type typeOf;
+
+  isArray = hasPrefix "a";
+  isMaybe = hasPrefix "m";
+  isTuple = hasPrefix "(";
+
+  # Returns the GVariant value that most closely matches the given Nix
+  # value. If no GVariant value can be found then `null` is returned.
+  #
+  # No support for dictionaries, maybe types, or variants.
+  mkValue = v:
+    if builtins.isBool v then
+      mkBoolean v
+    else if builtins.isInt v then
+      mkInt32 v
+    else if builtins.isFloat v then
+      mkDouble v
+    else if builtins.isString v then
+      mkString v
+    else if builtins.isList v then
+      if v == [ ] then mkArray type.string [ ] else mkArray (elemTypeOf v) v
+    else if builtins.isAttrs v && (v._type or "") == "gvariant" then
+      v
+    else
+      null;
+
+  mkArray = elemType: elems:
+    mkPrimitive (type.arrayOf elemType) (map mkValue elems) // {
+      __toString = self:
+        "@${self.type} [${concatMapStringsSep "," toString self.value}]";
+    };
+
+  mkEmptyArray = elemType: mkArray elemType [ ];
+
+  mkNothing = elemType: mkMaybe elemType null;
+
+  mkJust = elem: let gvarElem = mkValue elem; in mkMaybe gvarElem.type gvarElem;
+
+  mkTuple = elems:
+    let
+      gvarElems = map mkValue elems;
+      tupleType = type.tupleOf (map (e: e.type) gvarElems);
+    in mkPrimitive tupleType gvarElems // {
+      __toString = self:
+        "@${self.type} (${concatMapStringsSep "," toString self.value})";
+    };
+
+  mkBoolean = v:
+    mkPrimitive type.boolean v // {
+      __toString = self: if self.value then "true" else "false";
+    };
+
+  mkString = v:
+    mkPrimitive type.string v // {
+      __toString = self: "'${escape [ "'" "\\" ] self.value}'";
+    };
+
+  mkObjectpath = v:
+    mkPrimitive type.string v // {
+      __toString = self: "objectpath '${escape [ "'" ] self.value}'";
+    };
+
+  mkUchar = mkPrimitive type.uchar;
+
+  mkInt16 = mkPrimitive type.int16;
+
+  mkUint16 = mkPrimitive type.uint16;
+
+  mkInt32 = v:
+    mkPrimitive type.int32 v // {
+      __toString = self: toString self.value;
+    };
+
+  mkUint32 = mkPrimitive type.uint32;
+
+  mkInt64 = mkPrimitive type.int64;
+
+  mkUint64 = mkPrimitive type.uint64;
+
+  mkDouble = v:
+    mkPrimitive type.double v // {
+      __toString = self: toString self.value;
+    };
+
+}