SIMD-0201: Create a Cluster Sysvar

proposals/0201-create-cluster-sysvar.md

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+---
+simd: "0201"
+title: Create Cluster Sysvar
+authors:
+  - [email protected]
+category: Standard
+type: Core
+status: Review
+created: 2024-11-22
+feature:
+---
+
+## Summary
+
+There should be a natively accessible Sysvar (like Rent or Clock) that provides
+Cluster details in order to determine the specific SVM environment.
+
+## Motivation
+
+It is currently not possible to determine which cluster a Solana program is
+executing on from within the program itself. This makes dynamic behavior based
+on different SVM environments difficult without requiring multiple builds of a
+single protocol. Native determination of the SVM cluster would improve DevEx and
+diminish opportunities to introduce bugs by allowing more dynamic program execution.
+
+## Alternatives Considered
+
+- **SDK Abstraction** - It would be possible but difficult to maintain separate
+SDKs per cluster or dynamic resolution based on genesis hash
+
+## New Terminology
+
+**ClusterDetails** - The sysvar structure which provides the relevant details
+for a program to determine which cluster it's executing on.
+
+## Detailed Design
+
+The following Cluster type and ClusterDetails struct would provide sufficient
+details for a program to properly determine the environment on which it's
+executing. String tags are included because using genesis hash alone is
+insufficient for clusters that don't guarantee permanence such as devnet,
+testnet, or roll-ups.
+
+```rust
+/// The cluster type, usually the first three with an optional named
+/// field for more diverse clusters (alt-devnets, roll-ups).
+#[repr(C)]
+pub enum ClusterType: {
+    mainnet,
+    devnet,
+    testnet,
+    other(String),
+}
+
+#[repr(C)]
+pub struct ClusterDetails {
+    /// The genesis hash for the cluster, guaranteed for mainnet but
+    /// possibly variable for other cluster types.
+    pub genesis_hash: Hash,
+    /// A named tag for the SVM chain on which the program is executing.
+    pub blockchain: String,
+    /// Cluster Type
+    pub cluster_type: ClusterType,
+}
+```
+
+## Impact
+
+Dynamic determination of cluster would allow programs to perform better
+validation of cluster-specific feature such as variable protocol fees,
+irreplicable PDAs or derivations, or variable features across different blockchains.
+
+## Security Considerations
+
+Certain named fields could be invalidated due to changes to the underlying SVM
+runtime. Program developers should be sure to validate and fail gracefully if
+unexpected changes occur.