Fix various clang-tidy lints

* some things that can throw are marked noexcept
  yet the linter seems to think not. Maybe they can't throw in practice.
  I would rather not have the UB possibility in pretty obvious cold
  paths.
* various default-case-missing complaints
* a fair pile of casts from integer to character, which are in fact
  deliberate.
* an instance of <https://clang.llvm.org/extra/clang-tidy/checks/bugprone/move-forwarding-reference.html>
* bugprone-not-null-terminated-result on handing a string to curl in
  chunks of bytes. our usage is fine.
* reassigning a unique_ptr by CRIMES instead of using release(), then
  using release() and ignoring the result. wild. let's use release() for
  its intended purpose.

Change-Id: Ic3e7affef12383576213a8a7c8145c27e662513d

src/libstore/content-address.cc

@@ -157,7 +157,7 @@ size_t StoreReferences::size() const
     return (self ? 1 : 0) + others.size();
 }
 
-ContentAddressWithReferences ContentAddressWithReferences::withoutRefs(const ContentAddress & ca) noexcept
+ContentAddressWithReferences ContentAddressWithReferences::withoutRefs(const ContentAddress & ca)
 {
     return std::visit(overloaded {
         [&](const TextIngestionMethod &) -> ContentAddressWithReferences {
@@ -177,7 +177,7 @@ ContentAddressWithReferences ContentAddressWithReferences::withoutRefs(const Con
 }
 
 std::optional<ContentAddressWithReferences> ContentAddressWithReferences::fromPartsOpt(
-    ContentAddressMethod method, Hash hash, StoreReferences refs) noexcept
+    ContentAddressMethod method, Hash hash, StoreReferences refs)
 {
     return std::visit(overloaded {
         [&](TextIngestionMethod _) -> std::optional<ContentAddressWithReferences> {

src/libstore/content-address.hh

@@ -255,7 +255,7 @@ struct ContentAddressWithReferences
      * Create a `ContentAddressWithReferences` from a mere
      * `ContentAddress`, by claiming no references.
      */
-    static ContentAddressWithReferences withoutRefs(const ContentAddress &) noexcept;
+    static ContentAddressWithReferences withoutRefs(const ContentAddress &);
 
     /**
      * Create a `ContentAddressWithReferences` from 3 parts:
@@ -270,7 +270,7 @@ struct ContentAddressWithReferences
      * returns for invalid combinations.
      */
     static std::optional<ContentAddressWithReferences> fromPartsOpt(
-        ContentAddressMethod method, Hash hash, StoreReferences refs) noexcept;
+        ContentAddressMethod method, Hash hash, StoreReferences refs);
 
     ContentAddressMethod getMethod() const;
 

src/libstore/filetransfer.cc

@@ -142,7 +142,7 @@ struct curlFileTransfer : public FileTransfer
         template<class T>
         void fail(T && e)
         {
-            failEx(std::make_exception_ptr(std::move(e)));
+            failEx(std::make_exception_ptr(std::forward<T>(e)));
         }
 
         LambdaSink finalSink;
@@ -270,6 +270,9 @@ struct curlFileTransfer : public FileTransfer
                 return 0;
             auto count = std::min(size * nitems, request.data->length() - readOffset);
             assert(count);
+            // Lint: this is turning a string into a byte array to hand to
+            // curl, which is fine.
+            // NOLINTNEXTLINE(bugprone-not-null-terminated-result)
             memcpy(buffer, request.data->data() + readOffset, count);
             readOffset += count;
             return count;

src/libstore/local-store.cc

@@ -1315,10 +1315,12 @@ StorePath LocalStore::addToStoreFromDump(Source & source0, std::string_view name
         auto oldSize = dump.size();
         constexpr size_t chunkSize = 65536;
         auto want = std::min(chunkSize, settings.narBufferSize - oldSize);
-        if (auto tmp = realloc(dumpBuffer.get(), oldSize + want)) {
-            dumpBuffer.release();
-            dumpBuffer.reset((char*) tmp);
+
+        auto *toRealloc = dumpBuffer.release();
+        if (auto realloced = realloc(toRealloc, oldSize + want)) {
+            dumpBuffer.reset((char*) realloced);
         } else {
+            free(toRealloc);
             throw std::bad_alloc();
         }
         auto got = 0;

src/libutil/logging.cc

@@ -69,8 +69,8 @@ public:
             case lvlWarn: c = '4'; break;
             case lvlNotice: case lvlInfo: c = '5'; break;
             case lvlTalkative: case lvlChatty: c = '6'; break;
-            case lvlDebug: case lvlVomit: c = '7'; break;
-            default: c = '7'; break; // should not happen, and missing enum case is reported by -Werror=switch-enum
+            case lvlDebug: case lvlVomit:
+            default: c = '7'; break; // default case should not happen, and missing enum case is reported by -Werror=switch-enum
             }
             prefix = std::string("<") + c + ">";
         }

src/libutil/source-path.cc

@@ -50,6 +50,7 @@ InputAccessor::DirEntries SourcePath::readDirectory() const
         case DT_REG: type = InputAccessor::Type::tRegular; break;
         case DT_LNK: type = InputAccessor::Type::tSymlink; break;
         case DT_DIR: type = InputAccessor::Type::tDirectory; break;
+        default: break; // unknown type
         }
         res.emplace(entry.name, type);
     }

tests/unit/libstore-support/tests/path.cc

@@ -32,13 +32,13 @@ Gen<StorePathName> Arbitrary<StorePathName>::arbitrary()
     for (size_t c = 0; c < len; ++c) {
         switch (auto i = *gen::inRange<uint8_t>(0, 10 + 2 * 26 + 6)) {
             case 0 ... 9:
-                pre += '0' + i;
+                pre += static_cast<uint8_t>('0' + i);
                 break;
             case 10 ... 35:
-                pre += 'A' + (i - 10);
+                pre += static_cast<uint8_t>('A' + (i - 10));
                 break;
             case 36 ... 61:
-                pre += 'a' + (i - 36);
+                pre += static_cast<uint8_t>('a' + (i - 36));
                 break;
             case 62:
                 pre += '+';

tests/unit/libstore/outputs-spec.cc

@@ -176,12 +176,14 @@ TEST(ExtendedOutputsSpec, many_carrot) {
         using nlohmann::literals::operator "" _json;         \
         ASSERT_EQ(                                           \
             STR ## _json,                                    \
+            /* NOLINTNEXTLINE(bugprone-macro-parentheses) */ \
             ((nlohmann::json) TYPE { VAL }));                \
     }                                                        \
                                                              \
     TEST(TYPE, NAME ## _from_json) {                         \
         using nlohmann::literals::operator "" _json;         \
         ASSERT_EQ(                                           \
+            /* NOLINTNEXTLINE(bugprone-macro-parentheses) */ \
             TYPE { VAL },                                    \
             (STR ## _json).get<TYPE>());                     \
     }

tests/unit/libutil-support/tests/terminal-code-eater.cc

@@ -26,6 +26,7 @@ void TerminalCodeEater::feed(char c, std::function<void(char)> on_char)
         // Just eat \r, since it is part of clearing a line
         case '\r':
             return;
+        default: break;
         }
         if constexpr (DEBUG_EATER) {
             std::cerr << "eater uneat" << MaybeHexEscapedChar{c} << "\n";