docs: add warning about manually closing accounts (#1490)

lang/src/accounts/account.rs

@@ -340,6 +340,13 @@ impl<'info, T: AccountSerialize + AccountDeserialize + Owner + Clone> AccountsEx
     }
 }
 
+/// This function is for INTERNAL USE ONLY.
+/// Do NOT use this function in a program.
+/// Manual closing of `Account<'info, T>` types is NOT supported.
+///
+/// Details: Using `close` with `Account<'info, T>` is not safe because
+/// it requires the `mut` constraint but for that type the constraint
+/// overwrites the "closed account" discriminator at the end of the instruction.
 impl<'info, T: AccountSerialize + AccountDeserialize + Owner + Clone> AccountsClose<'info>
     for Account<'info, T>
 {

lang/src/accounts/account_loader.rs

@@ -231,6 +231,13 @@ impl<'info, T: ZeroCopy + Owner> AccountsExit<'info> for AccountLoader<'info, T>
     }
 }
 
+/// This function is for INTERNAL USE ONLY.
+/// Do NOT use this function in a program.
+/// Manual closing of `AccountLoader<'info, T>` types is NOT supported.
+///
+/// Details: Using `close` with `AccountLoader<'info, T>` is not safe because
+/// it requires the `mut` constraint but for that type the constraint
+/// overwrites the "closed account" discriminator at the end of the instruction.
 impl<'info, T: ZeroCopy + Owner> AccountsClose<'info> for AccountLoader<'info, T> {
     fn close(&self, sol_destination: AccountInfo<'info>) -> Result<()> {
         crate::common::close(self.to_account_info(), sol_destination)

lang/src/accounts/loader.rs

@@ -174,6 +174,13 @@ impl<'info, T: ZeroCopy> AccountsExit<'info> for Loader<'info, T> {
     }
 }
 
+/// This function is for INTERNAL USE ONLY.
+/// Do NOT use this function in a program.
+/// Manual closing of `Loader<'info, T>` types is NOT supported.
+///
+/// Details: Using `close` with `Loader<'info, T>` is not safe because
+/// it requires the `mut` constraint but for that type the constraint
+/// overwrites the "closed account" discriminator at the end of the instruction.
 #[allow(deprecated)]
 impl<'info, T: ZeroCopy> AccountsClose<'info> for Loader<'info, T> {
     fn close(&self, sol_destination: AccountInfo<'info>) -> Result<()> {

lang/src/accounts/program_account.rs

@@ -104,6 +104,13 @@ impl<'info, T: AccountSerialize + AccountDeserialize + Clone> AccountsExit<'info
     }
 }
 
+/// This function is for INTERNAL USE ONLY.
+/// Do NOT use this function in a program.
+/// Manual closing of `ProgramAccount<'info, T>` types is NOT supported.
+///
+/// Details: Using `close` with `ProgramAccount<'info, T>` is not safe because
+/// it requires the `mut` constraint but for that type the constraint
+/// overwrites the "closed account" discriminator at the end of the instruction.
 #[allow(deprecated)]
 impl<'info, T: AccountSerialize + AccountDeserialize + Clone> AccountsClose<'info>
     for ProgramAccount<'info, T>