Document 0.7.0 changes.

docs/070-breaking-changes.rst

@@ -8,13 +8,113 @@ affected code.
 For the full list check
 `the release changelog <https://github.com/ethereum/solidity/releases/tag/v0.7.0>`_.
 
+
+Silent Changes of the Semantics
+===============================
+
+ * Exponentiation and shifts of literals by non-literals (e.g. ``1 << x`` or ``2 ** x``)
+   will always use either the type ``uint256`` (for non-negative literals) or
+   ``int256`` (for negative literals) to perform the operation.
+   Previously, the operation was performed in the type of the shift amount / the
+   exponent which can be misleading.
+
+
+Changes to the Syntax
+=====================
+
+ * In external function and contract creation calls, Ether and gas is now specified using a new syntax:
+   ``x.f{gas: 10000, value: 2 ether}(arg1, arg2)``.
+   The old syntax -- ``x.f.gas(10000).value(2 ether)(arg1, arg2)`` -- will cause an error.
+ * The global variable ``now`` is deprecated, ``block.timestamp`` should be used instead.
+   The single identifier ``now`` is too generic for a global variable and could give the impression
+   that it changes during transaction processing, whereas ``block.timestamp`` correctly
+   reflects the fact that it is just a property of the block.
+ * NatSpec comments on variables are only allowed for public state variables and not
+   for local or internal variables.
+
+ * The token ``gwei`` is a keyword now (used to specify, e.g. ``2 gwei`` as a number)
+   and cannot be used as an identifier.
+
+ * State Mutability: The state mutability of functions can now be restricted during inheritance:
+   Functions with default state mutability can be overridden by ``pure`` and ``view`` functions
+   while ``view`` functions can be overridden by ``pure`` functions.
+   At the same time, public state variables are considered ``view`` and even ``pure``
+   if they are constants.
+
+
+
+Inline Assembly
+---------------
+
+ * Disallow ``.`` in user-defined function and variable names in inline assembly.
+   It is still valid if you use Solidity in Yul-only mode.
+
+ * Slot and offset of storage pointer variable ``x`` are accessed via ``x.slot``
+   and ``x.offset`` instead of ``x_slot`` and ``x_offset``.
+
+Removal of Unused or Unsafe Features
+====================================
+
+Mappings outside Storage
+------------------------
+
+ * If a struct or array contains a mapping, it can only be used in storage.
+   Previously, mapping members were silently skipped in memory, which
+   is confusing and error-prone.
+
+ * Assignments to structs or arrays in storage does not work if they contain
+   mappings.
+   Previously, mappings were silently skipped during the copy operation, which
+   is misleading and error-prone.
+
+Functions and Events
+--------------------
+
+ * Visibility (``public`` / ``external``) is not needed for constructors anymore:
+   To prevent a contract from being created, it can be marked ``abstract``.
+   This makes the visibility concept for constructors obsolete.
+
+ * Type Checker: Disallow ``virtual`` for library functions:
+   Since libraries cannot be inherited from, library functions should not be virtual.
+
+ * Multiple events with the same name and parameter types in the same
+   inheritance hierarchy are disallowed.
+
+ * ``using A for B`` only affects the contract it is mentioned in.
+   Previously, the effect was inherited. Now, you have to repeat the ``using``
+   statement in all derived contracts that make use of the feature.
+
+Expressions
+-----------
+
+ * Shifts by signed types are disallowed.
+   Previously, shifts by negative amounts were allowed, but reverted at runtime.
+
+ * The ``finney`` and ``szabo`` denominations are removed.
+   They are rarely used and do not make the actual amount readily visible. Instead, explicit
+   values like ``1e20`` or the very common ``gwei`` can be used.
+
+Declarations
+------------
+
+ * The keyword ``var`` cannot be used anymore.
+   Previously, this keyword would parse but result in a type error and
+   a suggestion about which type to use. Now, it results in a parser error.
+
+Interface Changes
+=================
+
+ * JSON AST: Members with value ``null`` are removed from JSON output.
+ * NatSpec: Constructors and functions have consistent userdoc output.
+
+
 How to update your code
 =======================
 
 This section gives detailed instructions on how to update prior code for every breaking change.
 
-* Change ``f.value(...)()`` to ``f{value: ...}()``. Similarly ``(new C).value(...)()`` to
-  ``(new C){value: ...}()`` and ``f.gas(...)()`` to ``f{gas: ...}()``.
+* Change ``x.f.value(...)()`` to ``x.f{value: ...}()``. Similarly ``(new C).value(...)()`` to
+  ``new C{value: ...}()`` and ``x.f.gas(...).value(...)()`` to ``x.f{gas: ..., value: ...}()``.
 * Change ``now`` to ``block.timestamp``.
 * Change types of right operand in shift operators to unsigned types. For example change ``x >> (256 - y)`` to
   ``x >> uint(256 - y)``.