libutil: inline ChainSource into sole remaining user

Change-Id: If0c81472a2e9b70e695631c147ce7eaae28d69d6

lix/libstore/local-store.cc

@@ -1346,6 +1346,27 @@ try {
     AutoCloseFD tempDirFd;
 
     if (!inMemory) {
+        struct ChainSource : Source
+        {
+            Source & source1, & source2;
+            bool useSecond = false;
+            ChainSource(Source & s1, Source & s2) : source1(s1), source2(s2) {}
+
+            size_t read(char * data, size_t len) override
+            {
+                if (useSecond) {
+                    return source2.read(data, len);
+                } else {
+                    try {
+                        return source1.read(data, len);
+                    } catch (EndOfFile &) {
+                        useSecond = true;
+                        return this->read(data, len);
+                    }
+                }
+            }
+        };
+
         /* Drain what we pulled so far, and then keep on pulling */
         StringSource dumpSource { dump };
         ChainSource bothSource { dumpSource, source };

lix/libutil/serialise.cc

@@ -321,18 +321,4 @@ void StringSink::operator () (std::string_view data)
     s.append(data);
 }
 
-size_t ChainSource::read(char * data, size_t len)
-{
-    if (useSecond) {
-        return source2.read(data, len);
-    } else {
-        try {
-            return source1.read(data, len);
-        } catch (EndOfFile &) {
-            useSecond = true;
-            return this->read(data, len);
-        }
-    }
-}
-
 }

lix/libutil/serialise.hh

@@ -324,21 +324,6 @@ struct LambdaSource : Source
     }
 };
 
-/**
- * Chain two sources together so after the first is exhausted, the second is
- * used
- */
-struct ChainSource : Source
-{
-    Source & source1, & source2;
-    bool useSecond = false;
-    ChainSource(Source & s1, Source & s2)
-        : source1(s1), source2(s2)
-    { }
-
-    size_t read(char * data, size_t len) override;
-};
-
 struct GeneratorSource : Source
 {
     GeneratorSource(Generator<Bytes> && g) : g(std::move(g)) {}