unluac 1.1.0

//! 这个文件负责把被前层机械拆开的相邻语句重新合并回更像源码的一次声明。
//!
//! 它依赖 binding/use 分析已经给出稳定引用关系，因此这里只合并“明显属于同一段
//! 源码声明”的 local/assign/temp-hoist 形状，而不会越权跨阶段重排有副作用的语句。
//! 这一步的目标是消掉 VM/结构恢复留下的机械拆分，不是随意把多条语句压成一行。
//!
//! 例子：
//! - `local a; a = f()` 会合成 `local a = f()`
//! - `local a = x; local b = y` 在两者确实属于同一组声明且后续使用形状允许时，
//!   会合成 `local a, b = x, y`
//! - 提前 hoist 出来的 `local t0; if cond then t0 = x end` 会尽量把 `t0` 下沉回
//!   真正使用它的分支/循环体里
//! - 如果同一条 hoisted 声明里前面的 carried binding 还要跨分支后缀继续活着，
//!   后面的 `staged` 之类一次性临时 binding 仍应允许单独沉回某个分支
//! - 但如果当前位置之前已经有会跳到更后面 label 的 forward goto，
//!   这里会停止继续下沉，避免生成“goto 跳进 local 作用域”的非法 Lua

use std::collections::BTreeSet;

use super::super::common::{
    AstBindingRef, AstBlock, AstLValue, AstLabelId, AstLocalAttr, AstLocalDecl, AstModule,
    AstNameRef, AstStmt,
};
use super::ReadabilityContext;
use super::binding_flow::{
    BindingUseIndex, block_references_any_binding, expr_references_any_binding,
    stmt_references_any_binding,
};
use super::expr_analysis::{expr_complexity, is_copy_like_expr};
use super::visit::{self, AstVisitor};
use super::walk::{self, AstRewritePass, BlockKind};

const ADJACENT_LOCAL_VALUE_COMPLEXITY_LIMIT: usize = 4;

pub(super) fn apply(module: &mut AstModule, context: ReadabilityContext) -> bool {
    let _ = context.target;
    walk::rewrite_module(module, &mut StatementMergePass)
}

struct StatementMergePass;

impl AstRewritePass for StatementMergePass {
    fn rewrite_block(&mut self, block: &mut AstBlock, _kind: BlockKind) -> bool {
        let mut changed = sink_hoisted_temp_decls(block);

        let old_stmts = std::mem::take(&mut block.stmts);
        let mut new_stmts = Vec::with_capacity(old_stmts.len());
        let mut index = 0;
        while index < old_stmts.len() {
            let Some(next_stmt) = old_stmts.get(index + 1) else {
                new_stmts.push(old_stmts[index].clone());
                index += 1;
                continue;
            };

            if let Some(merged) = try_merge_local_decl_with_assign(&old_stmts[index], next_stmt) {
                new_stmts.push(AstStmt::LocalDecl(Box::new(merged)));
                changed = true;
                index += 2;
                continue;
            }

            new_stmts.push(old_stmts[index].clone());
            index += 1;
        }

        block.stmts = new_stmts;
        changed |= merge_adjacent_single_value_local_decls(block);
        changed
    }
}

fn merge_adjacent_single_value_local_decls(block: &mut AstBlock) -> bool {
    let old_stmts = std::mem::take(&mut block.stmts);
    let use_index = BindingUseIndex::for_stmts(&old_stmts);
    let mut new_stmts = Vec::with_capacity(old_stmts.len());
    let mut changed = false;
    let mut index = 0;

    while index < old_stmts.len() {
        let Some((binding, value)) = single_value_local_decl(&old_stmts[index]) else {
            new_stmts.push(old_stmts[index].clone());
            index += 1;
            continue;
        };
        if !is_mergeable_adjacent_local_value(value) {
            new_stmts.push(old_stmts[index].clone());
            index += 1;
            continue;
        }

        let mut bindings = vec![binding.clone()];
        let mut values = vec![value.clone()];
        let mut lookahead = index + 1;
        while let Some((next_binding, next_value)) =
            old_stmts.get(lookahead).and_then(single_value_local_decl)
        {
            // 这里故意只收“连续复制/lookup”式的 local：
            // 目标是把 `local a = x; local b = y; local c = t[k]` 这类明显属于同一段
            // 源码声明的机械拆分重新压回去，而不是把有阶段语义的复杂 local 都并成一行。
            if !is_mergeable_adjacent_local_value(next_value)
                || expr_references_any_binding(next_value, &bindings)
            {
                break;
            }
            bindings.push(next_binding.clone());
            values.push(next_value.clone());
            lookahead += 1;
        }

        // 只把多次使用的 binding 纳入合并组；单次使用的 binding 留给 inline_exprs
        // 去内联。否则 `local a = x; local b = t.f; local c = T.K` 中 b/c 只用一次，
        // 却因为 a 多次使用而被一起合并成 multi-local，导致 inline_exprs 无法识别。
        // 为了不破坏声明顺序，从连续序列尾部剥离单次使用的 binding。
        while bindings.len() >= 2
            && use_index.count_uses_in_suffix(lookahead, bindings.last().unwrap().id) <= 1
        {
            bindings.pop();
            values.pop();
            lookahead -= 1;
        }

        if bindings.len() >= 2
            && bindings
                .iter()
                .any(|b| use_index.count_uses_in_suffix(lookahead, b.id) > 1)
        {
            new_stmts.push(AstStmt::LocalDecl(Box::new(AstLocalDecl {
                bindings,
                values,
            })));
            changed = true;
            index = lookahead;
            continue;
        }

        new_stmts.push(old_stmts[index].clone());
        index += 1;
    }

    block.stmts = new_stmts;
    changed
}

fn sink_hoisted_temp_decls(block: &mut AstBlock) -> bool {
    let mut changed = false;
    let mut index = 0;
    while index < block.stmts.len() {
        let Some(pending_bindings) = hoisted_temp_bindings(&block.stmts[index]) else {
            index += 1;
            continue;
        };
        let use_index = BindingUseIndex::for_stmts(&block.stmts);

        let mut remaining = pending_bindings;
        let mut pinned: Vec<super::super::common::AstLocalBinding> = Vec::new();
        let mut sink_changed = false;
        let mut lookahead = index + 1;
        while lookahead < block.stmts.len() && !remaining.is_empty() {
            if block_has_forward_goto_past_index(&block.stmts, lookahead) {
                lookahead += 1;
                continue;
            }
            if let Some(merged) =
                try_sink_hoisted_decl_into_stmt(&remaining, &block.stmts[lookahead])
            {
                let consumed = merged.bindings.len();
                block.stmts[lookahead] = AstStmt::LocalDecl(Box::new(merged));
                remaining.drain(..consumed);
                sink_changed = true;
                lookahead += 1;
                continue;
            }
            if let Some(attempt) = try_sink_hoisted_decl_into_nested_stmt_anywhere(
                &remaining,
                &block.stmts[lookahead],
                &use_index,
                lookahead + 1,
            ) {
                block.stmts[lookahead] = attempt.rewritten;
                remaining.drain(attempt.start..(attempt.start + attempt.consumed));
                sink_changed = true;
                // 不要前进 lookahead：同一条 if / loop 语句可能还有其它分支可以
                // 接收剩余 binding。例如 `local t12, t7; if ... then t12 = A else
                // t7 = B end` —— 第一轮把 t12 沉进 then，第二轮把 t7 沉进 else。
                continue;
            }
            if let Some((start, merged)) = try_sink_hoisted_decl_into_stmt_anywhere(
                &remaining,
                &block.stmts[lookahead],
                &use_index,
                lookahead + 1,
            ) {
                let consumed = merged.bindings.len();
                block.stmts[lookahead] = AstStmt::LocalDecl(Box::new(merged));
                remaining.drain(start..start + consumed);
                sink_changed = true;
                lookahead += 1;
                continue;
            }
            if stmt_references_any_binding(&block.stmts[lookahead], &remaining) {
                // 钉住被引用但无法下沉的 binding：它们的声明必须留在提升位置，
                // 但其他 binding 仍然可能被下沉到后续语句里。
                let mut i = 0;
                while i < remaining.len() {
                    if stmt_references_any_binding(
                        &block.stmts[lookahead],
                        std::slice::from_ref(&remaining[i]),
                    ) {
                        pinned.push(remaining.remove(i));
                    } else {
                        i += 1;
                    }
                }
                lookahead += 1;
                continue;
            }
            lookahead += 1;
        }

        if !sink_changed {
            index += 1;
            continue;
        }

        changed = true;

        // 将钉住的（不可下沉的）binding 合并回 remaining，按原始声明顺序
        // 排序，以保证输出的 `local` 列表确定且可读。
        remaining.extend(pinned);
        remaining.sort_by_key(|b| b.id);

        if remaining.is_empty() {
            block.stmts.remove(index);
            continue;
        }

        let AstStmt::LocalDecl(local_decl) = &mut block.stmts[index] else {
            unreachable!("hoisted temp decl scan must point at local decl");
        };
        local_decl.bindings = remaining;
        index += 1;
    }
    changed
}

struct NestedSinkAttempt {
    rewritten: AstStmt,
    start: usize,
    consumed: usize,
}

fn try_sink_hoisted_decl_into_nested_stmt_anywhere(
    pending: &[super::super::common::AstLocalBinding],
    stmt: &AstStmt,
    use_index: &BindingUseIndex,
    suffix_start: usize,
) -> Option<NestedSinkAttempt> {
    for start in 0..pending.len() {
        if use_index.count_uses_in_suffix(suffix_start, pending[start].id) != 0 {
            continue;
        }

        let mut end = start;
        while end < pending.len()
            && use_index.count_uses_in_suffix(suffix_start, pending[end].id) == 0
        {
            end += 1;
        }

        // 这里允许跳过前面仍需跨后缀存活的 carried binding，只把后面“只在某个嵌套块里
        // 用完”的 hoisted local 单独沉进去；否则像
        // `local next, staged; if ... else staged = ...; next = staged end`
        // 这种形状会因为 `next` 还要在 if 之后继续用，把 `staged` 也一起卡在块顶。
        for slice_end in (start + 1..=end).rev() {
            if let Some((rewritten, consumed)) = try_sink_hoisted_decl_into_nested_stmt(
                &pending[start..slice_end],
                stmt,
                use_index,
                suffix_start,
            ) {
                return Some(NestedSinkAttempt {
                    rewritten,
                    start,
                    consumed,
                });
            }
        }
    }

    None
}

fn try_sink_hoisted_decl_into_nested_stmt(
    pending: &[super::super::common::AstLocalBinding],
    stmt: &AstStmt,
    use_index: &BindingUseIndex,
    suffix_start: usize,
) -> Option<(AstStmt, usize)> {
    let sinkable_len = pending
        .iter()
        .take_while(|binding| use_index.count_uses_in_suffix(suffix_start, binding.id) == 0)
        .count();
    if sinkable_len == 0 {
        return None;
    }
    let sinkable = &pending[..sinkable_len];

    match stmt {
        AstStmt::If(if_stmt) => {
            if expr_references_any_binding(&if_stmt.cond, sinkable) {
                return None;
            }
            let then_refs = block_references_any_binding(&if_stmt.then_block, sinkable);
            let else_refs = if_stmt
                .else_block
                .as_ref()
                .is_some_and(|block| block_references_any_binding(block, sinkable));
            if then_refs == else_refs {
                return None;
            }

            let mut rewritten = stmt.clone();
            let target_block = match &mut rewritten {
                AstStmt::If(if_stmt) if then_refs => &mut if_stmt.then_block,
                AstStmt::If(if_stmt) => if_stmt
                    .else_block
                    .as_mut()
                    .expect("else refs imply else block"),
                _ => unreachable!("rewritten stmt must remain if"),
            };
            let consumed = sink_pending_bindings_into_block(target_block, sinkable);
            (consumed > 0).then_some((rewritten, consumed))
        }
        AstStmt::While(while_stmt) => {
            if expr_references_any_binding(&while_stmt.cond, sinkable) {
                return None;
            }
            let mut rewritten = stmt.clone();
            let AstStmt::While(while_stmt) = &mut rewritten else {
                unreachable!("rewritten stmt must remain while");
            };
            let consumed = sink_pending_bindings_into_block(&mut while_stmt.body, sinkable);
            (consumed > 0).then_some((rewritten, consumed))
        }
        AstStmt::Repeat(repeat_stmt) => {
            if expr_references_any_binding(&repeat_stmt.cond, sinkable) {
                return None;
            }
            let mut rewritten = stmt.clone();
            let AstStmt::Repeat(repeat_stmt) = &mut rewritten else {
                unreachable!("rewritten stmt must remain repeat");
            };
            let consumed = sink_pending_bindings_into_block(&mut repeat_stmt.body, sinkable);
            (consumed > 0).then_some((rewritten, consumed))
        }
        AstStmt::NumericFor(numeric_for) => {
            if expr_references_any_binding(&numeric_for.start, sinkable)
                || expr_references_any_binding(&numeric_for.limit, sinkable)
                || expr_references_any_binding(&numeric_for.step, sinkable)
            {
                return None;
            }
            let mut rewritten = stmt.clone();
            let AstStmt::NumericFor(numeric_for) = &mut rewritten else {
                unreachable!("rewritten stmt must remain numeric-for");
            };
            let consumed = sink_pending_bindings_into_block(&mut numeric_for.body, sinkable);
            (consumed > 0).then_some((rewritten, consumed))
        }
        AstStmt::GenericFor(generic_for) => {
            if generic_for
                .iterator
                .iter()
                .any(|expr| expr_references_any_binding(expr, sinkable))
            {
                return None;
            }
            let mut rewritten = stmt.clone();
            let AstStmt::GenericFor(generic_for) = &mut rewritten else {
                unreachable!("rewritten stmt must remain generic-for");
            };
            let consumed = sink_pending_bindings_into_block(&mut generic_for.body, sinkable);
            (consumed > 0).then_some((rewritten, consumed))
        }
        AstStmt::DoBlock(inner) => {
            let mut rewritten = AstBlock {
                stmts: inner.stmts.clone(),
            };
            let consumed = sink_pending_bindings_into_block(&mut rewritten, sinkable);
            (consumed > 0).then_some((AstStmt::DoBlock(Box::new(rewritten)), consumed))
        }
        AstStmt::FunctionDecl(_)
        | AstStmt::LocalFunctionDecl(_)
        | AstStmt::LocalDecl(_)
        | AstStmt::GlobalDecl(_)
        | AstStmt::Assign(_)
        | AstStmt::CallStmt(_)
        | AstStmt::Return(_)
        | AstStmt::Break
        | AstStmt::Continue
        | AstStmt::Goto(_)
        | AstStmt::Label(_) | AstStmt::Error(_) => None,
    }
}

fn sink_pending_bindings_into_block(
    block: &mut AstBlock,
    pending: &[super::super::common::AstLocalBinding],
) -> usize {
    let use_index = BindingUseIndex::for_stmts(&block.stmts);
    let mut consumed = 0usize;
    let mut index = 0usize;
    while index < block.stmts.len() && consumed < pending.len() {
        let remaining = &pending[consumed..];
        if block_has_forward_goto_past_index(&block.stmts, index) {
            index += 1;
            continue;
        }
        if let Some(merged) = try_sink_hoisted_decl_into_stmt(remaining, &block.stmts[index]) {
            let merged_len = merged.bindings.len();
            block.stmts[index] = AstStmt::LocalDecl(Box::new(merged));
            consumed += merged_len;
            index += 1;
            continue;
        }
        if let Some((rewritten, nested_consumed)) = try_sink_hoisted_decl_into_nested_stmt(
            remaining,
            &block.stmts[index],
            &use_index,
            index + 1,
        ) {
            block.stmts[index] = rewritten;
            consumed += nested_consumed;
            index += 1;
            continue;
        }
        if stmt_references_any_binding(&block.stmts[index], remaining) {
            // 该 binding 在此语句中被使用，但无法直接合并或下沉到嵌套块里
            // （例如在某个嵌套 `if` 内赋值但在后续兄弟节点中读取）。
            // 在此语句前插入裸 `local` 声明，使声明处于最窄的包围作用域。
            let decl = AstStmt::LocalDecl(Box::new(AstLocalDecl {
                bindings: remaining.to_vec(),
                values: vec![],
            }));
            block.stmts.insert(index, decl);
            consumed += remaining.len();
            break;
        }
        index += 1;
    }
    consumed
}

fn single_value_local_decl(
    stmt: &AstStmt,
) -> Option<(
    &super::super::common::AstLocalBinding,
    &super::super::common::AstExpr,
)> {
    let AstStmt::LocalDecl(local_decl) = stmt else {
        return None;
    };
    let [binding] = local_decl.bindings.as_slice() else {
        return None;
    };
    let [value] = local_decl.values.as_slice() else {
        return None;
    };
    (binding.attr == AstLocalAttr::None).then_some((binding, value))
}

fn try_merge_local_decl_with_assign(current: &AstStmt, next: &AstStmt) -> Option<AstLocalDecl> {
    let AstStmt::LocalDecl(local_decl) = current else {
        return None;
    };
    let AstStmt::Assign(assign) = next else {
        return None;
    };
    if !local_decl.values.is_empty() || local_decl.bindings.is_empty() {
        return None;
    }
    if local_decl
        .bindings
        .iter()
        .any(|binding| binding.attr != AstLocalAttr::None)
    {
        return None;
    }
    if local_decl.bindings.len() != assign.targets.len() || assign.values.is_empty() {
        return None;
    }
    if !local_decl
        .bindings
        .iter()
        .zip(assign.targets.iter())
        .all(|(binding, target)| local_binding_matches_target(binding.id, target))
    {
        return None;
    }

    Some(AstLocalDecl {
        bindings: local_decl.bindings.clone(),
        values: assign.values.clone(),
    })
}

fn hoisted_temp_bindings(stmt: &AstStmt) -> Option<Vec<super::super::common::AstLocalBinding>> {
    let AstStmt::LocalDecl(local_decl) = stmt else {
        return None;
    };
    if !local_decl.values.is_empty() || local_decl.bindings.is_empty() {
        return None;
    }
    if local_decl
        .bindings
        .iter()
        .any(|binding| binding.attr != AstLocalAttr::None || !is_temp_like_binding(binding.id))
    {
        return None;
    }
    Some(local_decl.bindings.clone())
}

fn try_sink_hoisted_decl_into_stmt(
    pending: &[super::super::common::AstLocalBinding],
    stmt: &AstStmt,
) -> Option<AstLocalDecl> {
    let AstStmt::Assign(assign) = stmt else {
        return None;
    };
    if assign.values.is_empty() || assign.targets.is_empty() || assign.targets.len() > pending.len()
    {
        return None;
    }
    let candidate = &pending[..assign.targets.len()];
    if !candidate
        .iter()
        .zip(assign.targets.iter())
        .all(|(binding, target)| local_binding_matches_target(binding.id, target))
    {
        return None;
    }
    if stmt_references_any_binding_in_assign(assign, &pending[assign.targets.len()..]) {
        return None;
    }
    Some(AstLocalDecl {
        bindings: candidate.to_vec(),
        values: assign.values.clone(),
    })
}

fn is_temp_like_binding(binding: AstBindingRef) -> bool {
    matches!(
        binding,
        AstBindingRef::Temp(_) | AstBindingRef::SyntheticLocal(_)
    )
}

/// 与 [`try_sink_hoisted_decl_into_stmt`] 类似，但在 `pending` 中任意位置搜索
/// 匹配的 binding，而非仅要求它们位于头部。成功时返回 `(start_index, AstLocalDecl)`，
/// 其中 `start_index` 是匹配 binding 在 `pending` 中的起始位置。
fn try_sink_hoisted_decl_into_stmt_anywhere(
    pending: &[super::super::common::AstLocalBinding],
    stmt: &AstStmt,
    use_index: &BindingUseIndex,
    suffix_start: usize,
) -> Option<(usize, AstLocalDecl)> {
    let AstStmt::Assign(assign) = stmt else {
        return None;
    };
    if assign.values.is_empty() || assign.targets.is_empty() || assign.targets.len() > pending.len()
    {
        return None;
    }
    let target_len = assign.targets.len();
    for start in 0..=pending.len() - target_len {
        let candidate = &pending[start..start + target_len];
        if !candidate
            .iter()
            .zip(assign.targets.iter())
            .all(|(binding, target)| local_binding_matches_target(binding.id, target))
        {
            continue;
        }
        // 只有当所有候选 binding 在此语句之后不再被使用时才允许下沉。
        if candidate
            .iter()
            .any(|b| use_index.count_uses_in_suffix(suffix_start, b.id) != 0)
        {
            continue;
        }
        // RHS 不得引用 consumed 切片之后的其他待处理 binding
        // （与前序变体相同的安全检查）。
        let after = &pending[start + target_len..];
        if !after.is_empty() && stmt_references_any_binding_in_assign(assign, after) {
            continue;
        }
        // 同样检查 consumed 切片之前的 binding。
        let before = &pending[..start];
        if !before.is_empty() && stmt_references_any_binding_in_assign(assign, before) {
            continue;
        }
        return Some((
            start,
            AstLocalDecl {
                bindings: candidate.to_vec(),
                values: assign.values.clone(),
            },
        ));
    }
    None
}

fn stmt_references_any_binding_in_assign(
    assign: &super::super::common::AstAssign,
    bindings: &[super::super::common::AstLocalBinding],
) -> bool {
    assign
        .values
        .iter()
        .any(|value| expr_references_any_binding(value, bindings))
}

fn is_mergeable_adjacent_local_value(expr: &super::super::common::AstExpr) -> bool {
    expr_complexity(expr) <= ADJACENT_LOCAL_VALUE_COMPLEXITY_LIMIT && is_copy_like_expr(expr)
}

fn local_binding_matches_target(binding: AstBindingRef, target: &AstLValue) -> bool {
    match (binding, target) {
        (AstBindingRef::Local(local), AstLValue::Name(AstNameRef::Local(target_local))) => {
            local == *target_local
        }
        (
            AstBindingRef::SyntheticLocal(local),
            AstLValue::Name(AstNameRef::SyntheticLocal(target_local)),
        ) => local == *target_local,
        (AstBindingRef::Temp(temp), AstLValue::Name(AstNameRef::Temp(target_temp))) => {
            temp == *target_temp
        }
        _ => false,
    }
}

fn block_has_forward_goto_past_index(stmts: &[AstStmt], index: usize) -> bool {
    let future_labels = stmts[(index + 1)..]
        .iter()
        .filter_map(|stmt| match stmt {
            AstStmt::Label(label) => Some(label.id),
            _ => None,
        })
        .collect::<BTreeSet<_>>();
    if future_labels.is_empty() {
        return false;
    }
    stmts[..index]
        .iter()
        .any(|stmt| stmt_contains_goto_to_any(stmt, &future_labels))
}

fn stmt_contains_goto_to_any(stmt: &AstStmt, targets: &BTreeSet<AstLabelId>) -> bool {
    let mut visitor = GotoTargetVisitor {
        targets,
        found: false,
    };
    visit::visit_stmt(stmt, &mut visitor);
    visitor.found
}

struct GotoTargetVisitor<'a> {
    targets: &'a BTreeSet<AstLabelId>,
    found: bool,
}

impl AstVisitor for GotoTargetVisitor<'_> {
    fn visit_stmt(&mut self, stmt: &AstStmt) {
        if let AstStmt::Goto(goto_stmt) = stmt
            && self.targets.contains(&goto_stmt.target)
        {
            self.found = true;
        }
    }

    fn visit_function_expr(&mut self, _function: &super::super::common::AstFunctionExpr) -> bool {
        false
    }
}

#[cfg(test)]
mod tests;