Split OutputsSpec and ExtendedOutputsSpec, use the former more

`DerivedPath::Built` and `DerivationGoal` were previously using a
regular set with the convention that the empty set means all outputs.
But it is easy to forget about this rule when processing those sets.
Using `OutputSpec` forces us to get it right.

src/libstore/outputs-spec.cc

@@ -6,57 +6,153 @@
 
 namespace nix {
 
-std::pair<std::string, ExtendedOutputsSpec> ExtendedOutputsSpec::parse(std::string s)
+bool OutputsSpec::contains(const std::string & outputName) const
 {
-    static std::regex regex(R"((.*)\^((\*)|([a-z]+(,[a-z]+)*)))");
+    return std::visit(overloaded {
+        [&](const OutputsSpec::All &) {
+            return true;
+        },
+        [&](const OutputsSpec::Names & outputNames) {
+            return outputNames.count(outputName) > 0;
+        },
+    }, raw());
+}
+
+
+std::optional<OutputsSpec> OutputsSpec::parseOpt(std::string_view s)
+{
+    static std::regex regex(R"((\*)|([a-z]+(,[a-z]+)*))");
 
     std::smatch match;
-    if (!std::regex_match(s, match, regex))
-        return {s, DefaultOutputs()};
+    std::string s2 { s }; // until some improves std::regex
+    if (!std::regex_match(s2, match, regex))
+        return std::nullopt;
 
-    if (match[3].matched)
-        return {match[1], AllOutputs()};
+    if (match[1].matched)
+        return { OutputsSpec::All {} };
 
-    return {match[1], tokenizeString<OutputNames>(match[4].str(), ",")};
+    if (match[2].matched)
+        return { tokenizeString<OutputsSpec::Names>(match[2].str(), ",") };
+
+    assert(false);
 }
 
+
+OutputsSpec OutputsSpec::parse(std::string_view s)
+{
+    std::optional spec = OutputsSpec::parseOpt(s);
+    if (!spec)
+        throw Error("Invalid outputs specifier: '%s'", s);
+    return *spec;
+}
+
+
+std::pair<std::string_view, ExtendedOutputsSpec> ExtendedOutputsSpec::parse(std::string_view s)
+{
+    auto found = s.rfind('^');
+
+    if (found == std::string::npos)
+        return { s, ExtendedOutputsSpec::Default {} };
+
+    auto spec = OutputsSpec::parse(s.substr(found + 1));
+    return { s.substr(0, found), ExtendedOutputsSpec::Explicit { spec } };
+}
+
+
+std::string OutputsSpec::to_string() const
+{
+    return std::visit(overloaded {
+        [&](const OutputsSpec::All &) -> std::string {
+            return "*";
+        },
+        [&](const OutputsSpec::Names & outputNames) -> std::string {
+            return concatStringsSep(",", outputNames);
+        },
+    }, raw());
+}
+
+
 std::string ExtendedOutputsSpec::to_string() const
 {
     return std::visit(overloaded {
         [&](const ExtendedOutputsSpec::Default &) -> std::string {
             return "";
         },
-        [&](const ExtendedOutputsSpec::All &) -> std::string {
-            return "*";
-        },
-        [&](const ExtendedOutputsSpec::Names & outputNames) -> std::string {
-            return "^" + concatStringsSep(",", outputNames);
+        [&](const ExtendedOutputsSpec::Explicit & outputSpec) -> std::string {
+            return "^" + outputSpec.to_string();
         },
     }, raw());
 }
 
+
+bool OutputsSpec::merge(const OutputsSpec & that)
+{
+    return std::visit(overloaded {
+        [&](OutputsSpec::All &) {
+            /* If we already refer to all outputs, there is nothing to do. */
+            return false;
+        },
+        [&](OutputsSpec::Names & theseNames) {
+            return std::visit(overloaded {
+                [&](const OutputsSpec::All &) {
+                    *this = OutputsSpec::All {};
+                    return true;
+                },
+                [&](const OutputsSpec::Names & thoseNames) {
+                    bool ret = false;
+                    for (auto & i : thoseNames)
+                        if (theseNames.insert(i).second)
+                            ret = true;
+                    return ret;
+                },
+            }, that.raw());
+        },
+    }, raw());
+}
+
+
+void to_json(nlohmann::json & json, const OutputsSpec & outputsSpec)
+{
+    std::visit(overloaded {
+        [&](const OutputsSpec::All &) {
+            json = std::vector<std::string>({"*"});
+        },
+        [&](const OutputsSpec::Names & names) {
+            json = names;
+        },
+    }, outputsSpec);
+}
+
+
 void to_json(nlohmann::json & json, const ExtendedOutputsSpec & extendedOutputsSpec)
 {
-    if (std::get_if<DefaultOutputs>(&extendedOutputsSpec))
-        json = nullptr;
-
-    else if (std::get_if<AllOutputs>(&extendedOutputsSpec))
-        json = std::vector<std::string>({"*"});
-
-    else if (auto outputNames = std::get_if<OutputNames>(&extendedOutputsSpec))
-        json = *outputNames;
+    std::visit(overloaded {
+        [&](const ExtendedOutputsSpec::Default &) {
+            json = nullptr;
+        },
+        [&](const ExtendedOutputsSpec::Explicit & e) {
+            to_json(json, e);
+        },
+    }, extendedOutputsSpec);
 }
 
+
+void from_json(const nlohmann::json & json, OutputsSpec & outputsSpec)
+{
+    auto names = json.get<OutputNames>();
+    if (names == OutputNames({"*"}))
+        outputsSpec = OutputsSpec::All {};
+    else
+        outputsSpec = names;
+}
+
+
 void from_json(const nlohmann::json & json, ExtendedOutputsSpec & extendedOutputsSpec)
 {
     if (json.is_null())
-        extendedOutputsSpec = DefaultOutputs();
+        extendedOutputsSpec = ExtendedOutputsSpec::Default {};
     else {
-        auto names = json.get<OutputNames>();
-        if (names == OutputNames({"*"}))
-            extendedOutputsSpec = AllOutputs();
-        else
-            extendedOutputsSpec = names;
+        extendedOutputsSpec = ExtendedOutputsSpec::Explicit { json.get<OutputsSpec>() };
     }
 }