func mergeConfigSrcs()

in extra/aws-sdk-go/aws/session/session.go [715:824]
91 lines of code
28 McCabe index (conditional complexity)

func mergeConfigSrcs(cfg, userCfg *aws.Config,
	envCfg envConfig, sharedCfg sharedConfig,
	handlers request.Handlers,
	sessOpts Options,
) error {

	// Region if not already set by user
	if len(aws.StringValue(cfg.Region)) == 0 {
		if len(envCfg.Region) > 0 {
			cfg.WithRegion(envCfg.Region)
		} else if envCfg.EnableSharedConfig && len(sharedCfg.Region) > 0 {
			cfg.WithRegion(sharedCfg.Region)
		}
	}

	if cfg.EnableEndpointDiscovery == nil {
		if envCfg.EnableEndpointDiscovery != nil {
			cfg.WithEndpointDiscovery(*envCfg.EnableEndpointDiscovery)
		} else if envCfg.EnableSharedConfig && sharedCfg.EnableEndpointDiscovery != nil {
			cfg.WithEndpointDiscovery(*sharedCfg.EnableEndpointDiscovery)
		}
	}

	// Regional Endpoint flag for STS endpoint resolving
	mergeSTSRegionalEndpointConfig(cfg, []endpoints.STSRegionalEndpoint{
		userCfg.STSRegionalEndpoint,
		envCfg.STSRegionalEndpoint,
		sharedCfg.STSRegionalEndpoint,
		endpoints.LegacySTSEndpoint,
	})

	// Regional Endpoint flag for S3 endpoint resolving
	mergeS3UsEast1RegionalEndpointConfig(cfg, []endpoints.S3UsEast1RegionalEndpoint{
		userCfg.S3UsEast1RegionalEndpoint,
		envCfg.S3UsEast1RegionalEndpoint,
		sharedCfg.S3UsEast1RegionalEndpoint,
		endpoints.LegacyS3UsEast1Endpoint,
	})

	var ec2IMDSEndpoint string
	for _, v := range []string{
		sessOpts.EC2IMDSEndpoint,
		envCfg.EC2IMDSEndpoint,
		sharedCfg.EC2IMDSEndpoint,
	} {
		if len(v) != 0 {
			ec2IMDSEndpoint = v
			break
		}
	}

	var endpointMode endpoints.EC2IMDSEndpointModeState
	for _, v := range []endpoints.EC2IMDSEndpointModeState{
		sessOpts.EC2IMDSEndpointMode,
		envCfg.EC2IMDSEndpointMode,
		sharedCfg.EC2IMDSEndpointMode,
	} {
		if v != endpoints.EC2IMDSEndpointModeStateUnset {
			endpointMode = v
			break
		}
	}

	if len(ec2IMDSEndpoint) != 0 || endpointMode != endpoints.EC2IMDSEndpointModeStateUnset {
		cfg.EndpointResolver = wrapEC2IMDSEndpoint(cfg.EndpointResolver, ec2IMDSEndpoint, endpointMode)
	}

	cfg.EC2MetadataEnableFallback = userCfg.EC2MetadataEnableFallback
	if cfg.EC2MetadataEnableFallback == nil && envCfg.EC2IMDSv1Disabled != nil {
		cfg.EC2MetadataEnableFallback = aws.Bool(!*envCfg.EC2IMDSv1Disabled)
	}
	if cfg.EC2MetadataEnableFallback == nil && sharedCfg.EC2IMDSv1Disabled != nil {
		cfg.EC2MetadataEnableFallback = aws.Bool(!*sharedCfg.EC2IMDSv1Disabled)
	}

	cfg.S3UseARNRegion = userCfg.S3UseARNRegion
	if cfg.S3UseARNRegion == nil {
		cfg.S3UseARNRegion = &envCfg.S3UseARNRegion
	}
	if cfg.S3UseARNRegion == nil {
		cfg.S3UseARNRegion = &sharedCfg.S3UseARNRegion
	}

	for _, v := range []endpoints.DualStackEndpointState{userCfg.UseDualStackEndpoint, envCfg.UseDualStackEndpoint, sharedCfg.UseDualStackEndpoint} {
		if v != endpoints.DualStackEndpointStateUnset {
			cfg.UseDualStackEndpoint = v
			break
		}
	}

	for _, v := range []endpoints.FIPSEndpointState{userCfg.UseFIPSEndpoint, envCfg.UseFIPSEndpoint, sharedCfg.UseFIPSEndpoint} {
		if v != endpoints.FIPSEndpointStateUnset {
			cfg.UseFIPSEndpoint = v
			break
		}
	}

	// Configure credentials if not already set by the user when creating the Session.
	// Credentials are resolved last such that all _resolved_ config values are propagated to credential providers.
	// ticket: P83606045
	if cfg.Credentials == credentials.AnonymousCredentials && userCfg.Credentials == nil {
		creds, err := resolveCredentials(cfg, envCfg, sharedCfg, handlers, sessOpts)
		if err != nil {
			return err
		}
		cfg.Credentials = creds
	}

	return nil
}