[gcc r12-3729] [Ada] Exception raised on empty file in GNATprove mode

[Pierre-Marie de Rodat <pmderodat@gcc.gnu.org>]

https://gcc.gnu.org/g:ea3789f6a2b868d9f440ddece64142d3a2cbcf1c

commit r12-3729-gea3789f6a2b868d9f440ddece64142d3a2cbcf1c
Author: Yannick Moy <moy@adacore.com>
Date:   Thu Jul 1 09:36:53 2021 +0200

    [Ada] Exception raised on empty file in GNATprove mode
    
    gcc/ada/
    
            * errout.adb (Get_Line_End): Do not allow the result to go past
            the end of the buffer.

Diff:
---
 gcc/ada/errout.adb | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/gcc/ada/errout.adb b/gcc/ada/errout.adb
index 0122304da6f..c859d8c5110 100644
--- a/gcc/ada/errout.adb
+++ b/gcc/ada/errout.adb
@@ -2473,7 +2473,8 @@ package body Errout is
          function Get_Line_End
            (Buf : Source_Buffer_Ptr;
             Loc : Source_Ptr) return Source_Ptr;
-         --  Get the source location for the end of the line in Buf for Loc
+         --  Get the source location for the end of the line in Buf for Loc. If
+         --  Loc is past the end of Buf already, return Buf'Last.
 
          function Get_Line_Start
            (Buf : Source_Buffer_Ptr;
@@ -2515,9 +2516,9 @@ package body Errout is
            (Buf : Source_Buffer_Ptr;
             Loc : Source_Ptr) return Source_Ptr
          is
-            Cur_Loc : Source_Ptr := Loc;
+            Cur_Loc : Source_Ptr := Source_Ptr'Min (Loc, Buf'Last);
          begin
-            while Cur_Loc <= Buf'Last
+            while Cur_Loc < Buf'Last
               and then Buf (Cur_Loc) /= ASCII.LF
             loop
                Cur_Loc := Cur_Loc + 1;