Assembly: Strict mode

[chriseth]

Assembly should be strict than currently defined. Issues should be warned about for now and turn into errors later. Only the following aspects of assembly should be allowed:

• directly below a block, only the following is allowed:
  • function definition
  • variable declaration
  • functional assignment
  • function call with zero returns
  • functional instruction that has zero returns
  • block
  • for
  • switch
  • break
  • continue
  • subassembly
• invalidJumpTag should be replaced by revert() / invalid()
• jumps are disallowed
• DUP and SWAP instructions are disallowed
• labels are disallowed
• statements (elements of a block) are disallowed if they return something onto the stack at the end.

[axic]

Need to add a flag to select parsing between "inline assembly" and Julia. In Julia mode it will:

• enable functions
• enable for statements
• enable switch statements
• enable tuple assignments with let
• enable types
• disable labels
• disable assignment from stack
• check that everything is assigned or discarded
• (potentially something else)

[axic]

Basically this means introducing a third option to the assembly stack, between the current "regular assembly" and julia mode. This mode is then used by the assembly keyword, but is not used by the solc --assemble mode.

[axic]

statements (elements of a block) are disallowed if they return something onto the stack at the end.

This should be fixed already with the stack balancing requirement.