Cosmos Dev Series: Cosmos-SDK-based Blockchain Upgrade - ModuleManager

module.go

func (m Manager) RunMigrations(ctx sdk.Context, cfg Configurator, fromVM VersionMap) (VersionMap, error) {
    ...
    
    updatedVM := VersionMap{}
    
    for _, moduleName := range modules {
        module := m.Modules[moduleName]
        fromVersion, exists := fromVM[moduleName]
        toVersion := module.ConsensusVersion()
        
        // We run migration if the module is specified in `fromVM`.
	// Otherwise we run InitGenesis.
	//
	// The module won't exist in the fromVM in two cases:
	// 1. A new module is added. In this case we run InitGenesis with an
	// empty genesis state.
	// 2. An existing chain is upgrading from version < 0.43 to v0.43+ for the first time.
	// In this case, all modules have yet to be added to x/upgrade's VersionMap store.
        if exists {
            err := c.runModuleMigrations(ctx, moduleName, fromVersion, toVersion)
            if err != nil {
                return nil, err
            }
        } 
        ...
        updatedVM[moduleName] = toVersion
    }
    
    return updatedVM, nil
}