Combined parsing and schema generations (libfetchers, WIP)

.gitignore

@@ -47,6 +47,9 @@ perl/Makefile.config
 /src/libexpr/nix.tbl
 /tests/unit/libexpr/libnixexpr-tests
 
+# /src/libfetchers/
+/src/libfetchers/tests/libnixfetchers-tests
+
 # /src/libstore/
 *.gen.*
 /tests/unit/libstore/libnixstore-tests

Makefile

@@ -30,6 +30,7 @@ makefiles += \
   tests/unit/libutil-support/local.mk \
   tests/unit/libstore/local.mk \
   tests/unit/libstore-support/local.mk \
+  tests/unit/libfetchers/local.mk \
   tests/unit/libexpr/local.mk \
   tests/unit/libexpr-support/local.mk
 endif

src/libexpr/value.hh

@@ -7,7 +7,7 @@
 
 #include "symbol-table.hh"
 #include "value/context.hh"
-#include "input-accessor.hh"
+#include "libfetchers/input-accessor.hh"
 
 #if HAVE_BOEHMGC
 #include <gc/gc_allocator.h>

src/libfetchers/attrs.cc

@@ -5,6 +5,14 @@
 
 namespace nix::fetchers {
 
+std::string attrType(const Attr &attr) {
+    return std::visit(overloaded {
+        [](const std::string &) { return "string"; },
+        [](const uint64_t &) { return "int"; },
+        [](const Explicit<bool> &) { return "bool"; },
+    }, attr);
+}
+
 Attrs jsonToAttrs(const nlohmann::json & json)
 {
     Attrs attrs;

src/libfetchers/attrs.hh

@@ -12,6 +12,9 @@
 
 namespace nix::fetchers {
 
+/**
+ * A primitive value that can be used in a fetcher attribute.
+ */
 typedef std::variant<std::string, uint64_t, Explicit<bool>> Attr;
 
 /**
@@ -21,6 +24,13 @@ typedef std::variant<std::string, uint64_t, Explicit<bool>> Attr;
  */
 typedef std::map<std::string, Attr> Attrs;
 
+/**
+ * A lowercase string designating the type of an `Attr`.
+ *
+ * Matches `builtins.typeOf` in Nix.
+ */
+std::string attrType(const Attr & attr);
+
 Attrs jsonToAttrs(const nlohmann::json & json);
 
 nlohmann::json attrsToJSON(const Attrs & attrs);

src/libfetchers/parser.cc

@@ -0,0 +1,59 @@
+#include "parser.hh"
+#include "schema.hh"
+
+namespace nix::fetchers {
+
+    // parsers::String
+
+    std::shared_ptr<Schema> parsers::String::getSchema() const {
+        return std::make_shared<Schema>(Schema::Primitive::String);
+    }
+
+    std::string parsers::String::parse (const nix::fetchers::Attr & in) const {
+        const std::string * r = std::get_if<std::string>(&in);
+        if (r)
+            return *r;
+        else
+            throw Error("expected a string, but value is of type " + attrType(in));
+    }
+
+    nix::fetchers::Attr parsers::String::unparse (const std::string & in) const {
+        return in;
+    }
+
+    // parsers::Int
+
+    std::shared_ptr<Schema> parsers::Int::getSchema() const {
+        return std::make_shared<Schema>(Schema::Primitive::Int);
+    }
+
+    uint64_t parsers::Int::parse (const nix::fetchers::Attr & in) const {
+        const uint64_t * r = std::get_if<uint64_t>(&in);
+        if (r)
+            return *r;
+        else
+            throw Error("expected an int, but value is of type " + attrType(in));
+    }
+
+    nix::fetchers::Attr parsers::Int::unparse (const uint64_t & in) const {
+        return in;
+    }
+
+    // parsers::Bool
+
+    std::shared_ptr<Schema> parsers::Bool::getSchema() const {
+        return std::make_shared<Schema>(Schema::Primitive::Bool);
+    }
+
+    bool parsers::Bool::parse (const nix::fetchers::Attr & in) const {
+        auto * r = std::get_if<Explicit<bool>>(&in);
+        if (r)
+            return r->t;
+        else
+            throw Error("expected a bool, but value is of type " + attrType(in));
+    }
+
+    nix::fetchers::Attr parsers::Bool::unparse (const bool & in) const {
+        return Explicit<bool>{in};
+    }
+}