I am writing a compiler for an embedded scripting language that will run in my application. I am currently working on the semantic analysis portion of the compiler. I would like to know, in theory, how to check that all code paths in a given script will return a value.
Doing a Google search on how to check if all code paths return a value yields only results about people seeing the error in their own code when not all code paths return a value (mostly SO questions), so I have been unable to find sources that explain how the actual checking can be done. Can anyone point me in the right direction?
NOTE: I am specifically looking for an authoritative source outlining a rigorous algorithm, if at all possible.
You can do this with a recursive walk over the AST. For example:
A sequence of statements returns on all control paths if either the first statement returns on all control paths or the second statement returns on all control paths.
An if statement returns on all control paths if both the "if" and "else" branches return on all control paths or the "if" statement is always true.
A while loop returns on all control paths only if the "while" condition is always true.
A return statement returns on all control paths.
Hope this helps!