Created attachment 357537 [details] [review]
Regression diffs generated by PostgreSQL

When running the regression tests of PostgreSQL with libxml2, I am getting many errors using the latest git master, like the following which invokes xmlCtxtReadDoc() using the XML parser, which creates additional error messages on top of the original ones of the stack:
! DETAIL:  line 1: switching encoding : no input                                                                                                                                                    

I have originally seen the error using ArchLinux package 2.9.4+96+gfb56f80e-1 which is based on commit fb56f80e of upstream libxml2, and the errors get away by using 2.9.4+4+g3169602-1, which is based on 3169602.

Bisecting manually this issue, I have found that the culprit commit is that one:
commit 46dc989080d5d6b7854de8fb3cb3de55ecbf0621
Author: Nick Wellnhofer <wellnhofer@aevum.de>
Date:   Thu Jun 8 02:24:56 2017 +0200

    Don't switch encoding for internal parameter entities
   
    This is only needed for external entities. Trying to switch the encoding
    for internal entities could also cause a memory leak in recovery mode.

I don't know much libxml2 code to draw a conclusion by myself, so input would be welcome.