In order to support representing source locations corresponding to an author’s original source different from the current source we should add #line and #endline support into WGSL.

Rename comment operator

The current comment operator is # this should be changed to // to make it clearer that the #line and #endline are not comments. This also provides room if we need to extend the tokens we accept after # in the future.

Restrictions on the String Literal

In order to handle strings with quotes in them, we need to allow escaped " and \ in the string literal.

The STRING_LITERAL token needs to be updated with the following:

• A string may contain a \\ which is translated to a single \
• A string may contain a \" which is translated to a single "
• A string may not contain a \0
• Otherwise, any UTF-8 character is valid within a string.

Syntax

#line 12 "a / filepath\""
...
#endline

The #line must be followed by a positive integer line number. The line number may be followed by an optional quoted string. A line number of 1 corresponds to the first line of an original source program.

Grammar updates

Add Tokens:

• LINE == #line
• ENDLINE == #endline

In order to support the directives they need to be add to both the statement and global_decl rules:

 | LINE INT_LITERAL STRING_LITERAL?
 | ENDLINE

This allows you to put the directives before any functions and within function bodies. It does not allow a #line or #endline to be inserted in the middle of another statement.

A #line directive may not appear as the last statement in a block.

Handling

The #line statement sets the line number in the parser until the next #line or #endline is encountered . They have no semantic effect.

The #endline restarts the parser counting line numbers. The line immediately after the #endline has a line number of 1 greater then the value set with the #line. If no #line was seen, the #endline has no effect and is counted as a regular line.

The usage of the #line operator is up to the processing software. It, should be passed through and emitted in the target language if possible.

In SPIR-V this will translate into OpLine and OpString entries for #line and OpNoLine for #endline. If the provided filename is blank the OpString will be an empty string.

%1 = OpString "a /filepath \""
         OpLine %1 12 0
...
         OpNoLIne