eng/coding-80cols: Convert wiki page to Rest

Converted https://devel.rtems.org/wiki/Developer/Coding/80_characters_per_line
to Rest, and TBDs into comments.

This work was part of GCI 2018.

eng/coding-80cols.rst

@@ -6,5 +6,149 @@
 Eighty Character Line Limit
 ***************************
 
-TBD  - Convert the following to Rest and insert into this file
-TBD - https://devel.rtems.org/wiki/Developer/Coding/80_characters_per_line
+.. COMMENT: TBD - Convert the following to Rest and insert into this file
+.. COMMENT: TBD - https://devel.rtems.org/wiki/Developer/Coding/80_characters_per_line
+
+ Code should look good for everyone under some standard width assumptions.
+ Where a line wraps should be the same for anyone reading the code. For
+ historical reasons, RTEMS uses 80 characters as the maximum width for each
+ line of code.
+
+If you find yourself with code longer than 80 characters, first ask yourself
+whether the nesting level is too deep, names too long, compound expressions too
+complicated, or if some other guideline for improving readability can help to
+shrink the line length. Refactoring nested blocks into functions can help to
+alleviate code width problems while improving code readability. Making names
+descriptive yet terse can also improve readability. If absolutely necessary
+to have a long line, follow the rules on this page to break the line up to adhere
+to the 80 characters per line rule.
+
+Breaking long lines
+-------------------
+
+``if``, ``while``, and ``for`` loops have their condition expressions aligned
+and broken on separate lines. When the conditions have to be broken, none go on
+the first line with the ``if``, ``while``, or ``for`` statement, and none go on
+the last line with the closing parenthesis and (optional) curly brace. Long
+statements are broken up and indented at operators, with an operator always
+being the last token on a line. No blank spaces should be left at the end of
+any line. Here is an example with a ``for`` loop.
+
+.. code-block:: c
+
+  for ( initialization = statement; a + really + long + statement + that + evaluates + to < a + boolean; another + statement++ ) {
+    z = a + really + long + statement + that + needs + two + lines + gets + indented + four + more + spaces + on + the + second + and + subsequent + lines + and + broken + up + at + operators;
+  }
+
+Should be replaced with
+
+.. code-block:: c
+
+  for (
+    initialization = statement;
+    a + really + long + statement + that + evaluates + to <
+    a + boolean;
+    another + statement++
+  ) {
+    z = a + really + long + statement + that + needs +
+        two + lines + gets + indented + four + more +
+        spaces + on + the + second + and + subsequent +
+        lines + and + broken + up + at + operators;
+  }
+
+Note that indentations should add 2 nesting levels (4 space characters, not tabs).
+
+Similarly,
+
+.. code-block:: c
+
+  if ( this + that < those && this + these < that && this + those < these && this < those && those < that ) {
+
+should be broken up like
+
+.. code-block:: c
+
+  if (
+    this + that < those &&
+    this + these < that &&
+    this + those < these &&
+    this < those &&
+    those < that
+  ) {
+
+Note that each expression that resolves to a boolean goes on its own line.
+Where you place the boolean operator is a matter of choice.
+
+When a line is long because of a comment at the end, move the comment to
+just before the line, for example
+
+.. code-block:: c
+
+  #define A_LONG_MACRO_NAME (AND + EXPANSION) /* Plus + a + really + long + comment */
+
+can be replaced with
+
+.. code-block:: c
+
+  /* Plus + a + really + long + comment */
+  #define A_LONG_MACRO_NAME (AND + EXPANSION)
+
+C Preprocessor macros need to be broken up with some care, because the
+preprocessor does not understand that it should eat newline characters. So
+
+.. code-block:: c
+
+  #define A_LONG_MACRO_NAME (AND + EXCESSIVELY + LONG + EXPANSION + WITH + LOTS + OF + EXTRA + STUFF + DEFINED)
+
+would become
+
+.. code-block:: c
+
+  #define A_LONG_MACRO_NAME ( \
+    AND + EXCESSIVELY + LONG + EXPANSION + WITH + LOTS + OF + EXTRA + STUFF + \
+    DEFINED \
+  )
+
+Notice that each line is terminated by a backslash then the carriage return.
+The backslash tells the preprocessor to eat the newline. Of course, if you have
+such a long macro, you should consider not using a macro.
+
+Function declarations can be broken up at each argument, for example
+
+.. code-block:: c
+
+  int this_is_a_function( int arg1, int arg2, int arg3, int arg4, int arg5, int arg6, int arg7, int arg8, int arg9 );
+
+would be broken up as
+
+.. code-block:: c
+
+  int this_is_a_function(
+    int arg1,
+    int arg2,
+    int arg3,
+    int arg4,
+    int arg5,
+    int arg6,
+    int arg7,
+    int arg8,
+    int arg9
+  );
+
+Excessively long comments should be broken up at a word boundary or somewhere
+that makes sense, for example
+
+.. code-block:: c
+
+  /* Excessively long comments should be broken up at a word boundary or somewhere that makes sense, for example */
+
+would be
+
+.. code-block:: c
+
+  /* Excessively long comments should be broken up at a word boundary or
+   * somewhere that makes sense, for example */
+
+Note that multiline comments have a single asterisk aligned with the asterisk
+in the opening ``/*``. The closing ``*/`` should go at the end of the last
+line.