Add -fsuppress-error-contexts to disable printing error contexts in errorswip/suppress-err-context

In many development environments, the source span is the primary means
of seeing what an error message relates to, and the In the expression:
and In an equation for: clauses are not particularly relevant. However,
they can grow to be quite long, which can make the message itself both
feel overwhelming and interact badly with limited-space areas.

It's simple to implement this flag so we might as well do it and give
the user control about how they see their messages.

Fixes #21722

1 files changed, 12 insertions, 0 deletions

diff --git a/docs/users_guide/using.rst b/docs/users_guide/using.rst
index ee61a89ce1..a3ccd2c168 100644
--- a/docs/users_guide/using.rst
+++ b/docs/users_guide/using.rst
@@ -1360,6 +1360,18 @@ messages and in GHCi:
     error was detected.  This also affects the associated caret symbol that
     points at the region of code at fault.
 
+.. ghc-flag:: -fsuppress-error-contexts
+    :shortdesc: Whether to show textual information about error context
+    :type: dynamic
+    :reverse: -fno-suppress-error-contexts
+    :category: verbosity
+
+    :default: off
+
+    Controls whether GHC displays information about the context in which an
+    error occurred. This controls whether the part of the error message which
+    says "In the equation..", "In the pattern.." etc is displayed or not.
+
 .. ghc-flag:: -ferror-spans
     :shortdesc: Output full span in error messages
     :type: dynamic