localVarRef

fn localVarRef(
    gz: *GenZir,
    scope: *Scope,
    ri: ResultInfo,
    ident: Ast.Node.Index,
    ident_token: Ast.TokenIndex,
) InnerError!Zir.Inst.Ref {
    const astgen = gz.astgen;
    const name_str_index = try astgen.identAsString(ident_token);
    var s = scope;
    var found_already: ?Ast.Node.Index = null; // we have found a decl with the same name already
    var found_needs_tunnel: bool = undefined; // defined when `found_already != null`
    var found_namespaces_out: u32 = undefined; // defined when `found_already != null`

    // The number of namespaces above `gz` we currently are
    var num_namespaces_out: u32 = 0;
    // defined by `num_namespaces_out != 0`
    var capturing_namespace: *Scope.Namespace = undefined;

    while (true) switch (s.tag) {
        .local_val => {
            const local_val = s.cast(Scope.LocalVal).?;

            if (local_val.name == name_str_index) {
                // Locals cannot shadow anything, so we do not need to look for ambiguous
                // references in this case.
                if (ri.rl == .discard and ri.ctx == .assignment) {
                    local_val.discarded = .fromToken(ident_token);
                } else {
                    local_val.used = .fromToken(ident_token);
                }

                if (local_val.is_used_or_discarded) |ptr| ptr.* = true;

                const value_inst = if (num_namespaces_out != 0) try tunnelThroughClosure(
                    gz,
                    ident,
                    num_namespaces_out,
                    .{ .ref = local_val.inst },
                    .{ .token = local_val.token_src },
                    name_str_index,
                ) else local_val.inst;

                return rvalueNoCoercePreRef(gz, ri, value_inst, ident);
            }
            s = local_val.parent;
        },
        .local_ptr => {
            const local_ptr = s.cast(Scope.LocalPtr).?;
            if (local_ptr.name == name_str_index) {
                if (ri.rl == .discard and ri.ctx == .assignment) {
                    local_ptr.discarded = .fromToken(ident_token);
                } else {
                    local_ptr.used = .fromToken(ident_token);
                }

                // Can't close over a runtime variable
                if (num_namespaces_out != 0 and !local_ptr.maybe_comptime and !gz.is_typeof) {
                    const ident_name = try astgen.identifierTokenString(ident_token);
                    return astgen.failNodeNotes(ident, "mutable '{s}' not accessible from here", .{ident_name}, &.{
                        try astgen.errNoteTok(local_ptr.token_src, "declared mutable here", .{}),
                        try astgen.errNoteNode(capturing_namespace.node, "crosses namespace boundary here", .{}),
                    });
                }

                switch (ri.rl) {
                    .ref, .ref_coerced_ty => {
                        const ptr_inst = if (num_namespaces_out != 0) try tunnelThroughClosure(
                            gz,
                            ident,
                            num_namespaces_out,
                            .{ .ref = local_ptr.ptr },
                            .{ .token = local_ptr.token_src },
                            name_str_index,
                        ) else local_ptr.ptr;
                        local_ptr.used_as_lvalue = true;
                        return ptr_inst;
                    },
                    else => {
                        const val_inst = if (num_namespaces_out != 0) try tunnelThroughClosure(
                            gz,
                            ident,
                            num_namespaces_out,
                            .{ .ref_load = local_ptr.ptr },
                            .{ .token = local_ptr.token_src },
                            name_str_index,
                        ) else try gz.addUnNode(.load, local_ptr.ptr, ident);
                        return rvalueNoCoercePreRef(gz, ri, val_inst, ident);
                    },
                }
            }
            s = local_ptr.parent;
        },
        .gen_zir => s = s.cast(GenZir).?.parent,
        .defer_normal, .defer_error => s = s.cast(Scope.Defer).?.parent,
        .namespace => {
            const ns = s.cast(Scope.Namespace).?;
            if (ns.decls.get(name_str_index)) |i| {
                if (found_already) |f| {
                    return astgen.failNodeNotes(ident, "ambiguous reference", .{}, &.{
                        try astgen.errNoteNode(f, "declared here", .{}),
                        try astgen.errNoteNode(i, "also declared here", .{}),
                    });
                }
                // We found a match but must continue looking for ambiguous references to decls.
                found_already = i;
                found_needs_tunnel = ns.maybe_generic;
                found_namespaces_out = num_namespaces_out;
            }
            num_namespaces_out += 1;
            capturing_namespace = ns;
            s = ns.parent;
        },
        .top => break,
    };
    if (found_already == null) {
        const ident_name = try astgen.identifierTokenString(ident_token);
        return astgen.failNode(ident, "use of undeclared identifier '{s}'", .{ident_name});
    }

    // Decl references happen by name rather than ZIR index so that when unrelated
    // decls are modified, ZIR code containing references to them can be unmodified.

    if (found_namespaces_out > 0 and found_needs_tunnel) {
        switch (ri.rl) {
            .ref, .ref_coerced_ty => return tunnelThroughClosure(
                gz,
                ident,
                found_namespaces_out,
                .{ .decl_ref = name_str_index },
                .{ .node = found_already.? },
                name_str_index,
            ),
            else => {
                const result = try tunnelThroughClosure(
                    gz,
                    ident,
                    found_namespaces_out,
                    .{ .decl_val = name_str_index },
                    .{ .node = found_already.? },
                    name_str_index,
                );
                return rvalueNoCoercePreRef(gz, ri, result, ident);
            },
        }
    }

    switch (ri.rl) {
        .ref, .ref_coerced_ty => return gz.addStrTok(.decl_ref, name_str_index, ident_token),
        else => {
            const result = try gz.addStrTok(.decl_val, name_str_index, ident_token);
            return rvalueNoCoercePreRef(gz, ri, result, ident);
        },
    }
}