fix(lang-v2): reject optional siblings in associated_token init const…

lang-v2/derive/src/parse.rs

@@ -1049,6 +1049,32 @@ fn parse_associated_token_init(
     }))
 }
 
+fn validate_associated_token_init_refs(
+    attrs: &AccountAttrs,
+    associated_token: Option<&AssociatedTokenInit>,
+    field_summaries: &[FieldSummary],
+) -> syn::Result<()> {
+    let Some(at) = associated_token else {
+        return Ok(());
+    };
+    if !(attrs.is_init || attrs.is_init_if_needed) {
+        return Ok(());
+    }
+
+    for ident in [&at.mint, &at.authority, &at.token_program] {
+        if field_is_optional(field_summaries, ident) {
+            return Err(syn::Error::new(
+                ident.span(),
+                format!(
+                    "`associated_token` constraints cannot reference optional account `{ident}` during init"
+                ),
+            ));
+        }
+    }
+
+    Ok(())
+}
+
 /// Wrap the `Result<Self>`-yielding `init_body` so that each runtime-only
 /// namespaced constraint's `AccountConstraint::init` fires against the
 /// freshly-typed value, then return the typed value. Producing this
@@ -2224,6 +2250,7 @@ pub fn parse_field(
     }
     let option_inner = extract_option_inner(field_ty);
     let associated_token = parse_associated_token_init(&attrs, field_names)?;
+    validate_associated_token_init_refs(&attrs, associated_token.as_ref(), field_summaries)?;
     let init_if_needed_reuse_validation = if attrs.is_init_if_needed {
         Some(emit_init_if_needed_reuse_validation(
             option_inner.unwrap_or(field_ty),

lang-v2/tests/macro_diagnostics.rs

@@ -1109,6 +1109,50 @@ pub struct Bad {
     );
 }
 
+#[test]
+#[cfg_attr(
+    miri,
+    ignore = "spawns cargo and writes temporary workspaces; covered by normal cargo test"
+)]
+fn associated_token_init_rejects_optional_sibling_refs() {
+    compile_fail_case(
+        "associated_token_init_rejects_optional_sibling_refs",
+        r#"
+use anchor_lang_v2::prelude::*;
+use anchor_spl_v2::{
+    associated_token::AssociatedToken,
+    mint::Mint,
+    token::{Token, TokenAccount},
+};
+
+#[account]
+pub struct Holder {
+    pub value: u64,
+}
+
+#[derive(Accounts)]
+pub struct Bad {
+    #[account(mut)]
+    pub payer: Signer,
+    pub mint: Option<Account<Mint>>,
+    pub authority: Option<Account<Holder>>,
+    pub token_program: Program<Token>,
+    #[account(
+        init,
+        payer = payer,
+        associated_token::mint = mint,
+        associated_token::authority = authority,
+        associated_token::token_program = token_program,
+    )]
+    pub token_account: Account<TokenAccount>,
+    pub associated_token_program: Program<AssociatedToken>,
+    pub system_program: Program<System>,
+}
+"#,
+        &["associated_token` constraints cannot reference optional account"],
+    );
+}
+
 #[test]
 #[cfg_attr(
     miri,