refactor: Enable more clang-tidy readability checks (#6595)

Co-authored-by: Sergey Kuznetsov <kuzzz99@gmail.com>

include/xrpl/beast/utility/instrumentation.h

@@ -15,7 +15,7 @@
 #define ALWAYS_OR_UNREACHABLE(cond, message) assert((message) && (cond))
 #define SOMETIMES(cond, message, ...)
 #define REACHABLE(message, ...)
-#define UNREACHABLE(message, ...) assert((message) && false)
+#define UNREACHABLE(message, ...) assert((message) && false)  // NOLINT(misc-static-assert)
 #endif
 
 #define XRPL_ASSERT ALWAYS_OR_UNREACHABLE

include/xrpl/core/JobQueue.h

@@ -316,7 +316,7 @@ private:
     // Returns the limit of running jobs for the given job type.
     // For jobs with no limit, we return the largest int. Hopefully that
     // will be enough.
-    int
+    static int
     getJobLimit(JobType type);
 };
 

include/xrpl/protocol/Permissions.h

@@ -72,12 +72,12 @@ public:
     isDelegable(std::uint32_t const& permissionValue, Rules const& rules) const;
 
     // for tx level permission, permission value is equal to tx type plus one
-    uint32_t
-    txToPermissionType(TxType const& type) const;
+    static uint32_t
+    txToPermissionType(TxType const& type);
 
     // tx type value is permission value minus one
-    TxType
-    permissionToTxType(uint32_t const& value) const;
+    static TxType
+    permissionToTxType(uint32_t const& value);
 };
 
 }  // namespace xrpl

include/xrpl/protocol/Serializer.h

@@ -336,7 +336,7 @@ public:
         static_assert(N > 0, "");
     }
 
-    std::size_t
+    [[nodiscard]] bool
     empty() const noexcept
     {
         return remain_ == 0;

include/xrpl/shamap/SHAMap.h

@@ -520,7 +520,7 @@ private:
     // getMissingNodes helper functions
     void
     gmn_ProcessNodes(MissingNodes&, MissingNodes::StackEntry& node);
-    void
+    static void
     gmn_ProcessDeferredReads(MissingNodes&);
 
     // fetch from DB helper function

include/xrpl/tx/ApplyContext.h

@@ -111,7 +111,7 @@ public:
     checkInvariants(TER const result, XRPAmount const fee);
 
 private:
-    TER
+    static TER
     failInvariantCheck(TER const result);
 
     template <std::size_t... Is>

include/xrpl/tx/invariants/FreezeInvariant.h

@@ -48,7 +48,7 @@ private:
     bool
     isValidEntry(std::shared_ptr<SLE const> const& before, std::shared_ptr<SLE const> const& after);
 
-    STAmount
+    static STAmount
     calculateBalanceChange(
         std::shared_ptr<SLE const> const& before,
         std::shared_ptr<SLE const> const& after,
@@ -63,7 +63,7 @@ private:
     std::shared_ptr<SLE const>
     findIssuer(AccountID const& issuerID, ReadView const& view);
 
-    bool
+    static bool
     validateIssuerChanges(
         std::shared_ptr<SLE const> const& issuer,
         IssuerChanges const& changes,
@@ -71,7 +71,7 @@ private:
         beast::Journal const& j,
         bool enforce);
 
-    bool
+    static bool
     validateFrozenState(
         BalanceChange const& change,
         bool high,

include/xrpl/tx/invariants/InvariantCheck.h

@@ -111,7 +111,7 @@ public:
     void
     visitEntry(bool, std::shared_ptr<SLE const> const&, std::shared_ptr<SLE const> const&);
 
-    bool
+    static bool
     finalize(STTx const&, TER const, XRPAmount const, ReadView const&, beast::Journal const&);
 };
 

include/xrpl/tx/invariants/LoanInvariant.h

@@ -41,8 +41,8 @@ class ValidLoanBroker
     // for LoanBroker pseudo-accounts.
     std::vector<SLE::const_pointer> mpts_;
 
-    bool
-    goodZeroDirectory(ReadView const& view, SLE::const_ref dir, beast::Journal const& j) const;
+    static bool
+    goodZeroDirectory(ReadView const& view, SLE::const_ref dir, beast::Journal const& j);
 
 public:
     void