How to modify SWIFT_MODULE_NAME?

SWIFT_MODULE_NAME, PRODUCT_MODULE_NAME, PRODUCT_NAME, EXECUTABLE_NAME

Default values:

EXECUTABLE_NAME = $EXECUTABLE_PREFIX$PRODUCT_NAME$EXECUTABLE_SUFFIX
SWIFT_OBJC_INTERFACE_HEADER_NAME = $(SWIFT_MODULE_NAME) 

SWIFT_MODULE_NAME = $(PRODUCT_MODULE_NAME)
PRODUCT_MODULE_NAME = $(PRODUCT_NAME:c99extidentifier)
PRODUCT_NAME = $(TARGET_NAME:c99extidentifier)

Observation:

SWIFT_MODULE_NAME == PRODUCT_MODULE_NAME

c99extidentifier

Xcode is able to substitute a value of variable c99extidentifier identifier which supports extended characters from C99

//for example
PRODUCT_NAME = My Framework
PRODUCT_MODULE_NAME = $(PRODUCT_NAME:c99extidentifier) = My_Framework

EXECUTABLE_NAME name of binary

Product Module Name(PRODUCT_MODULE_NAME) determines how the import statement will look like. For example when you are creating a Library or a Framework.

Using:

//Objective-C
@import module_name; 

//Swift
import module_name 

Product Name(PRODUCT_NAME) determines the name of binary. E.g. MyFramework.framework

[TARGET_NAME]

Rule is:

SWIFT_MODULE_NAME should equal to PRODUCT_MODULE_NAME

[Custom .modulemap]

The module name comes from the Product Module Name build setting:

The SWIFT_MODULE_NAME setting is apparently hidden, but you can see its derivation by looking at Xcode.app/Contents/PlugIns/Xcode3Core.ideplugin/Contents/SharedSupport/Developer/Library/Xcode/Plug-ins/XCLanguageSupport.xcplugin/Contents/Resources/Swift.xcspec:

...
{
    Name = "SWIFT_MODULE_NAME";
    Type = String;
    DefaultValue = "$(PRODUCT_MODULE_NAME)";
    CommandLineArgs = (
        "-module-name",
        "$(value)",
    );
},
...