From fedfc913ad75984b476e7838d6254c547f9134d5 Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Sun, 12 Jul 2020 16:12:21 +0000
Subject: [PATCH] Use more std::visit to prepare for new variant

N.B. not using `std::visit` for fetchurl because there is no attempt to
handle all the cases (e.g. no `else`) and lambda complicates early
return.
---
 src/libstore/derivations.cc | 32 +++++++++++++++++++-------------
 src/libstore/derivations.hh |  5 ++++-
 src/nix/show-derivation.cc  | 13 +++++++++----
 3 files changed, 32 insertions(+), 18 deletions(-)

diff --git a/src/libstore/derivations.cc b/src/libstore/derivations.cc
index ce2025933..09683a005 100644
--- a/src/libstore/derivations.cc
+++ b/src/libstore/derivations.cc
@@ -283,13 +283,16 @@ string Derivation::unparse(const Store & store, bool maskOutputs,
         if (first) first = false; else s += ',';
         s += '('; printUnquotedString(s, i.first);
         s += ','; printUnquotedString(s, maskOutputs ? "" : store.printStorePath(i.second.path(store, name)));
-        if (auto hash = std::get_if<DerivationOutputFixed>(&i.second.output)) {
-            s += ','; printUnquotedString(s, hash->hash.printMethodAlgo());
-            s += ','; printUnquotedString(s, hash->hash.hash.to_string(Base16, false));
-        } else {
-            s += ','; printUnquotedString(s, "");
-            s += ','; printUnquotedString(s, "");
-        }
+        std::visit(overloaded {
+            [&](DerivationOutputInputAddressed doi) {
+                s += ','; printUnquotedString(s, "");
+                s += ','; printUnquotedString(s, "");
+            },
+            [&](DerivationOutputFixed dof) {
+                s += ','; printUnquotedString(s, dof.hash.printMethodAlgo());
+                s += ','; printUnquotedString(s, dof.hash.hash.to_string(Base16, false));
+            },
+        }, i.second.output);
         s += ')';
     }
 
@@ -503,12 +506,15 @@ void writeDerivation(Sink & out, const Store & store, const BasicDerivation & dr
     for (auto & i : drv.outputs) {
         out << i.first
             << store.printStorePath(i.second.path(store, drv.name));
-        if (auto hash = std::get_if<DerivationOutputFixed>(&i.second.output)) {
-            out << hash->hash.printMethodAlgo()
-                << hash->hash.hash.to_string(Base16, false);
-        } else {
-            out << "" << "";
-        }
+        std::visit(overloaded {
+            [&](DerivationOutputInputAddressed doi) {
+                out << "" << "";
+            },
+            [&](DerivationOutputFixed dof) {
+                out << dof.hash.printMethodAlgo()
+                    << dof.hash.hash.to_string(Base16, false);
+            },
+        }, i.second.output);
     }
     writeStorePaths(store, out, drv.inputSrcs);
     out << drv.platform << drv.builder << drv.args;
diff --git a/src/libstore/derivations.hh b/src/libstore/derivations.hh
index fd8828373..4dc542536 100644
--- a/src/libstore/derivations.hh
+++ b/src/libstore/derivations.hh
@@ -25,7 +25,10 @@ struct DerivationOutputFixed
 
 struct DerivationOutput
 {
-    std::variant<DerivationOutputInputAddressed, DerivationOutputFixed> output;
+    std::variant<
+        DerivationOutputInputAddressed,
+        DerivationOutputFixed
+    > output;
     StorePath path(const Store & store, std::string_view drvName) const;
 };
 
diff --git a/src/nix/show-derivation.cc b/src/nix/show-derivation.cc
index a868023d4..f9952e177 100644
--- a/src/nix/show-derivation.cc
+++ b/src/nix/show-derivation.cc
@@ -70,10 +70,15 @@ struct CmdShowDerivation : InstallablesCommand
                 for (auto & output : drv.outputs) {
                     auto outputObj(outputsObj.object(output.first));
                     outputObj.attr("path", store->printStorePath(output.second.path(*store, drv.name)));
-                    if (auto hash = std::get_if<DerivationOutputFixed>(&output.second.output)) {
-                        outputObj.attr("hashAlgo", hash->hash.printMethodAlgo());
-                        outputObj.attr("hash", hash->hash.hash.to_string(Base16, false));
-                    }
+
+                    std::visit(overloaded {
+                        [&](DerivationOutputInputAddressed doi) {
+                        },
+                        [&](DerivationOutputFixed dof) {
+                            outputObj.attr("hashAlgo", dof.hash.printMethodAlgo());
+                            outputObj.attr("hash", dof.hash.hash.to_string(Base16, false));
+                        },
+                    }, output.second.output);
                 }
             }