You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: _policy_generation_details.rs
    path of file: ./repos/aws-sdk-rust/sdk/accessanalyzer/src/types
    
    the code of the file until where you have to start completion: // Code generated by software.amazon.smithy.rust.codegen.smithy-rs. DO NOT EDIT.

/// <p>Contains the ARN details about the IAM entity for which the policy is generated.</p>
#[non_exhaustive]
#[derive(::std::clone::Clone, ::std::cmp::PartialEq, ::std::fmt::Debug)]
pub struct PolicyGenerationDetails {
    /// <p>The ARN of the IAM entity (user or role) for which you are generating a policy.</p>
    pub principal_arn: ::std::string::String,
}
impl PolicyGenerationDetails {
    /// <p>The ARN of the IAM
    
    pub fn build(self) -> ::std::result::Result<crate::types::PolicyGenerationDetails, ::aws_smithy_types::error::operation::BuildError> {
        ::std::result::Result::Ok(crate::types::PolicyGenerationDetails {
            principal_arn: self.principal_arn.ok_or_else(|| {
                ::aws_smithy_types::error::operation::BuildError::missing_field(
                    "principal_arn",
                    "principal_arn was not specified but it is required when building PolicyGenerationDetails",
                )
            })?,
        })
    }