Add a typetest for types flowing through transaction message functions

.changeset/three-nights-decide.md

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+---
+'@solana/transaction-messages': minor
+'@solana/instruction-plans': minor
+'@solana/transactions': minor
+'@solana/signers': minor
+'@solana/kit': minor
+---
+
+Return more precise types from transaction message functions
+
+Deprecate `BaseTransactionMessage` in favour of `TransactionMessage`

packages/kit/src/__typetests__/scenarios/transaction-message-decompile-modify-typetest.ts

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+// [DESCRIBE] A scenario testing the types of transaction-message functionality
+// Based on discussion/examples from https://github.com/anza-xyz/kit/pull/1103
+
+import { Address } from '@solana/addresses';
+import { pipe } from '@solana/functional';
+import { Instruction } from '@solana/instructions';
+import { GetMultipleAccountsApi, Rpc } from '@solana/rpc';
+import { setTransactionMessageFeePayerSigner, TransactionSigner } from '@solana/signers';
+import {
+    appendTransactionMessageInstruction,
+    appendTransactionMessageInstructions,
+    BlockhashLifetimeConstraint,
+    CompiledTransactionMessage,
+    CompiledTransactionMessageWithLifetime,
+    prependTransactionMessageInstruction,
+    prependTransactionMessageInstructions,
+    setTransactionMessageFeePayer,
+    setTransactionMessageLifetimeUsingBlockhash,
+    setTransactionMessageLifetimeUsingDurableNonce,
+    TransactionMessage,
+} from '@solana/transaction-messages';
+
+import { decompileTransactionMessageFetchingLookupTables } from '../../decompile-transaction-message-fetching-lookup-tables';
+
+const compiledTransactionMessage = null as unknown as CompiledTransactionMessage &
+    CompiledTransactionMessageWithLifetime;
+const rpc = null as unknown as Rpc<GetMultipleAccountsApi>;
+
+type TransactionMessageNotLegacy = Exclude<TransactionMessage, { version: 'legacy' }>;
+
+void (async () => {
+    const transactionMessage = await decompileTransactionMessageFetchingLookupTables(compiledTransactionMessage, rpc);
+
+    // @ts-expect-error Transaction has an unknown version
+    transactionMessage satisfies TransactionMessageNotLegacy;
+    if (transactionMessage.version === 0) {
+        // It typechecks when the transaction message is known to be v0
+        transactionMessage satisfies TransactionMessageNotLegacy;
+    }
+
+    // We update the transaction message using update functions to ensure the types flow correctly
+    const blockhash = null as unknown as BlockhashLifetimeConstraint;
+    const durableNonce = null as unknown as Parameters<typeof setTransactionMessageLifetimeUsingDurableNonce>[0];
+    const feePayer = null as unknown as Address;
+    const instruction = null as unknown as Instruction;
+    const signer = null as unknown as TransactionSigner;
+
+    const updatedMessage = pipe(
+        transactionMessage,
+        m => setTransactionMessageLifetimeUsingBlockhash(blockhash, m),
+        m => setTransactionMessageLifetimeUsingDurableNonce(durableNonce, m),
+        m => setTransactionMessageFeePayer(feePayer, m),
+        m => appendTransactionMessageInstruction(instruction, m),
+        m => appendTransactionMessageInstructions([instruction], m),
+        m => prependTransactionMessageInstruction(instruction, m),
+        m => prependTransactionMessageInstructions([instruction], m),
+        m => setTransactionMessageFeePayerSigner(signer, m),
+    );
+
+    // @ts-expect-error Transaction has an unknown version
+    updatedMessage satisfies TransactionMessageNotLegacy;
+    if (updatedMessage.version === 0) {
+        // It typechecks when the transaction message is known to be v0
+        updatedMessage satisfies TransactionMessageNotLegacy;
+    }
+})();