Fixes bug where prev_mapping was not being set when file_id == 1

slither/printers/summary/evm.py

@@ -95,6 +95,9 @@ class PrinterEVM(AbstractPrinter):
         for idx, mapping in enumerate(srcmap_runtime):
             # Parse srcmap_runtime according to its format
             # See https://solidity.readthedocs.io/en/v0.5.9/miscellaneous.html#source-mappings
+            # In order to compress these source mappings especially for bytecode, the following rules are used:
+            # If a field is empty, the value of the preceding element is used.
+            # If a : is missing, all following fields are considered empty.
 
             mapping_item = mapping.split(':')
             mapping_item += prev_mapping[len(mapping_item):]
@@ -104,6 +107,7 @@ class PrinterEVM(AbstractPrinter):
                     mapping_item[i] = int(prev_mapping[i])
                     
             offset, length, file_id, _ = mapping_item
+            prev_mapping = mapping_item
             
             if file_id == '-1':
                 # Internal compiler-generated code snippets to be ignored
@@ -118,6 +122,4 @@ class PrinterEVM(AbstractPrinter):
             # Note: The order depends on how solc creates the srcmap_runtime
             source_to_evm_mapping.setdefault(line_number, []).append(evm_instructions[idx].pc)
             
-            prev_mapping = mapping_item
-            
         return(source_to_evm_mapping)