Merge bitcoin#22597: consensus/params: simplify ValidDeployment check to avoid gcc warning

0591710 consensus/params: simplify ValidDeployment check to avoid gcc warning (Anthony Towns)

Pull request description:

  Simplifies the ValidDeployment check to only check the upperbound, relying on the lower bound to be trivially true due to enum values starting at the minimum value of the underlying type (which is checked at compile time in deploymentstatus.cpp). Avoids a "comparison always true" warning in some versions of gcc.

  Fixes bitcoin#22587

ACKs for top commit:
  MarcoFalke:
    review ACK 0591710
  tryphe:
    retested ACK 0591710

Tree-SHA512: e53b5d478b46d35ec476d004e3c92803afb874c138dd6ef3848861f4281cc113fe88921bc4ac74fd4decbf318ed776d3f816c3a1185f99dc36a5cfecfff51f7c

Author: MarcoFalke

src/consensus/params.h

@@ -23,15 +23,15 @@ enum BuriedDeployment : int16_t {
     DEPLOYMENT_CSV,
     DEPLOYMENT_SEGWIT,
 };
-constexpr bool ValidDeployment(BuriedDeployment dep) { return DEPLOYMENT_HEIGHTINCB <= dep && dep <= DEPLOYMENT_SEGWIT; }
+constexpr bool ValidDeployment(BuriedDeployment dep) { return dep <= DEPLOYMENT_SEGWIT; }
 
 enum DeploymentPos : uint16_t {
     DEPLOYMENT_TESTDUMMY,
     DEPLOYMENT_TAPROOT, // Deployment of Schnorr/Taproot (BIPs 340-342)
     // NOTE: Also add new deployments to VersionBitsDeploymentInfo in deploymentinfo.cpp
     MAX_VERSION_BITS_DEPLOYMENTS
 };
-constexpr bool ValidDeployment(DeploymentPos dep) { return DEPLOYMENT_TESTDUMMY <= dep && dep <= DEPLOYMENT_TAPROOT; }
+constexpr bool ValidDeployment(DeploymentPos dep) { return dep < MAX_VERSION_BITS_DEPLOYMENTS; }
 
 /**
  * Struct for each individual consensus rule change using BIP9.

src/deploymentstatus.cpp

@@ -7,6 +7,8 @@
 #include <consensus/params.h>
 #include <versionbits.h>
 
+#include <type_traits>
+
 VersionBitsCache g_versionbitscache;
 
 /* Basic sanity checking for BuriedDeployment/DeploymentPos enums and
@@ -15,3 +17,18 @@ VersionBitsCache g_versionbitscache;
 static_assert(ValidDeployment(Consensus::DEPLOYMENT_TESTDUMMY), "sanity check of DeploymentPos failed (TESTDUMMY not valid)");
 static_assert(!ValidDeployment(Consensus::MAX_VERSION_BITS_DEPLOYMENTS), "sanity check of DeploymentPos failed (MAX value considered valid)");
 static_assert(!ValidDeployment(static_cast<Consensus::BuriedDeployment>(Consensus::DEPLOYMENT_TESTDUMMY)), "sanity check of BuriedDeployment failed (overlaps with DeploymentPos)");
+
+/* ValidDeployment only checks upper bounds for ensuring validity.
+ * This checks that the lowest possible value or the type is also a
+ * (specific) valid deployment so that lower bounds don't need to be checked.
+ */
+
+template<typename T, T x>
+static constexpr bool is_minimum()
+{
+    using U = typename std::underlying_type<T>::type;
+    return x == std::numeric_limits<U>::min();
+}
+
+static_assert(is_minimum<Consensus::BuriedDeployment, Consensus::DEPLOYMENT_HEIGHTINCB>(), "heightincb is not minimum value for BuriedDeployment");
+static_assert(is_minimum<Consensus::DeploymentPos, Consensus::DEPLOYMENT_TESTDUMMY>(), "testdummy is not minimum value for DeploymentPos");