GitLab

During parsing, GHC collects lexical information about AST nodes and
stores it in a map. It is needed to faithfully restore original source
code, e.g. compare these expressions:

	a =  b
	a  = b

The position of the equality sign is not recorded in the AST, so it must
be stored elsewhere.

This system is described in Note [Api annotations].

Before this patch, the mapping was represented by:

	Map (SrcSpan, AnnKeywordId) SrcSpan

After this patch, the mapping is represented by:

	Map (RealSrcSpan, AnnKeywordId) RealSrcSpan

The motivation behind this change is to avoid using the Ord SrcSpan
instance (required by Map here), as it interferes with #17632 (see the
discussion there).

SrcSpan is isomorphic to  Either String RealSrcSpan,  but we shouldn't
use those strings as Map keys. Those strings are intended as hints to
the user, e.g. "<interactive>" or "<compiler-generated code>", so they
are not a valid way to identify nodes in the source code.

The parens around the kinded tyvars should be attached to the class
declaration as a whole, they are attached to the tyvar instead,
outside the span.

An annotation must always be within or after the span it is contained
in.

Closes #16212

This reverts commit 76c8fd67.

For an API annotation to be useful, it must not occur before the span
it is enclosed in.

So, for check-api-annotation output, a line such as

((Test16212.hs:3:22-36,AnnOpenP), [Test16212.hs:3:21]),

should be flagged as an error, as the AnnOpenP location of 3:21
precedes its enclosing span of 3:22-26.

This patch does this.

Closes #16217