tryExpr

fn tryExpr(
    parent_gz: *GenZir,
    scope: *Scope,
    ri: ResultInfo,
    node: Ast.Node.Index,
    operand_node: Ast.Node.Index,
) InnerError!Zir.Inst.Ref {
    const astgen = parent_gz.astgen;

    const fn_block = astgen.fn_block orelse {
        return astgen.failNode(node, "'try' outside function scope", .{});
    };

    if (parent_gz.any_defer_node.unwrap()) |any_defer_node| {
        return astgen.failNodeNotes(node, "'try' not allowed inside defer expression", .{}, &.{
            try astgen.errNoteNode(
                any_defer_node,
                "defer expression here",
                .{},
            ),
        });
    }

    // Ensure debug line/column information is emitted for this try expression.
    // Then we will save the line/column so that we can emit another one that goes
    // "backwards" because we want to evaluate the operand, but then put the debug
    // info back at the try keyword for error return tracing.
    if (!parent_gz.is_comptime) {
        try emitDbgNode(parent_gz, node);
    }
    const try_lc: LineColumn = .{ astgen.source_line - parent_gz.decl_line, astgen.source_column };

    const operand_rl: ResultInfo.Loc, const block_tag: Zir.Inst.Tag = switch (ri.rl) {
        .ref, .ref_coerced_ty => .{ .ref, .try_ptr },
        .ref_const => .{ .ref_const, .try_ptr },
        else => .{ .none, .@"try" },
    };
    const operand_ri: ResultInfo = .{ .rl = operand_rl, .ctx = .error_handling_expr };
    const operand = operand: {
        // As a special case, we need to detect this form:
        // `try .foo(...)`
        // This is a decl literal form, even though we don't propagate a result type through `try`.
        var buf: [1]Ast.Node.Index = undefined;
        if (astgen.tree.fullCall(&buf, operand_node)) |full_call| {
            const res_ty: Zir.Inst.Ref = try ri.rl.resultType(parent_gz, operand_node) orelse .none;
            break :operand try callExpr(parent_gz, scope, operand_ri, res_ty, operand_node, full_call);
        }

        // This could be a pointer or value depending on the `ri` parameter.
        break :operand try reachableExpr(parent_gz, scope, operand_ri, operand_node, node);
    };

    const try_inst = try parent_gz.makeBlockInst(block_tag, node);
    try parent_gz.instructions.append(astgen.gpa, try_inst);

    var else_scope = parent_gz.makeSubBlock(scope);
    defer else_scope.unstack();

    const err_tag = switch (ri.rl) {
        .ref, .ref_const, .ref_coerced_ty => Zir.Inst.Tag.err_union_code_ptr,
        else => Zir.Inst.Tag.err_union_code,
    };
    const err_code = try else_scope.addUnNode(err_tag, operand, node);
    try genDefers(&else_scope, &fn_block.base, scope, .normal_and_error);
    try emitDbgStmt(&else_scope, try_lc);
    _ = try else_scope.addUnNode(.ret_node, err_code, node);

    try else_scope.setTryBody(try_inst, operand);
    const result = try_inst.toRef();
    switch (ri.rl) {
        .ref, .ref_const, .ref_coerced_ty => return result,
        else => return rvalue(parent_gz, ri, result, node),
    }
}