D2 is really that stable as it is claimed to be?

[Timon Gehr]

On 09/22/2013 02:33 AM, Walter Bright wrote:
> On 9/21/2013 5:11 PM, Sean Kelly wrote:
>>> Tracking the column number is certainly doable, but it comes at a
>>> cost of
>>> memory consumption and some compile speed, since it has to be tracked in
>>> every token. I used to do it in the Digital Mars C compiler, but it
>>> was of
>>> only marginal utility and I dropped it.
>>
>> Can't you just hold a pointer to the beginning of the line and
>> subtract to
>> find the column?  I agree that it's generally of marginal utility though.
>
> Holding the pointer has a cost of memory consumption and compile speed
> :-)

(The current scheme is not optimal either.)

struct Loc
{
     const char *filename; // <--
     unsigned linnum;

Replace this pointer by a pointer or (global) offset to the first 
character in the source file buffer corresponding to the AST node. The 
file name can be recovered from this using an appropriate data structure.

In order to find the first column index, decode backwards until you hit 
a newline character or the beginning of the source file.

In order to find the last column index if that is wanted, re-invoke the 
parser. (Personally, I just store a slice into the source buffer.)

This allows the compiler to underline the location where an error occurred:

tt.d:7:14: error: need 'this' to access field 'S.member'
     auto x = S.member;
              ^~~~~~~~
tt.d:3:5: note: field was declared here
     int member;
     ^~~~~~~~~~~

Editors understand this format and can quickly jump to the location.

You could also get rid of linnum by splitting the source file buffer 
into lines on demand and using binary search.

> as well as having to have the source file buffer stay around
> throughout the compile  ...

Which, as far as I understand, DMD does anyway? If you do not want to 
keep it around, release it and reload it on demand if an error actually 
occurs in that buffer. (Time taken to spit out an error message does not 
need to be optimized that much.)