[Ada] Fix PR ada/81106

[Eric Botcazou]

As reported and analyzed in the PR, gnatchop does not correctly propagate a 
BOM present in the source file to the first compilation unit it outputs, in 
the case where the -r switch is specified, because it copies the BOM for the 
first compilation unit as part of the chopping process instead of copying it 
specifically at the start of the unit.

Tested on x86-64/Linux, applied on the mainline.


2025-11-24  Eric Botcazou  <ebotca...@adacore.com>

        PR ada/81106
        * gnatchop.adb (Gnatchop): If present in the source file, output
        the BOM at the start of every compilation unit.

-- 
Eric Botcazou
diff --git a/gcc/ada/gnatchop.adb b/gcc/ada/gnatchop.adb
index bc045e1fb7a..286904a2378 100644
--- a/gcc/ada/gnatchop.adb
+++ b/gcc/ada/gnatchop.adb
@@ -138,7 +138,7 @@ procedure Gnatchop is
       --  Line number from GNAT output line
 
       Offset : File_Offset;
-      --  Offset name from GNAT output line
+      --  Offset from GNAT output line
 
       SR_Present : Boolean;
       --  Set True if SR parameter present
@@ -1319,8 +1319,7 @@ procedure Gnatchop is
       Success : Boolean;
       TS_Time : OS_Time;
 
-      BOM_Present : Boolean;
-      BOM         : BOM_Kind;
+      BOM : BOM_Kind;
       --  Record presence of UTF8 BOM in input
 
    begin
@@ -1347,7 +1346,6 @@ procedure Gnatchop is
       --  Test for presence of BOM
 
       Read_BOM (Buffer.all, BOM_Length, BOM, XML_Support => False);
-      BOM_Present := BOM /= Unknown;
 
       --  Only chop those units that come from this file
 
@@ -1357,7 +1355,7 @@ procedure Gnatchop is
               (Source    => Buffer,
                Num       => Unit_Number,
                TS_Time   => TS_Time,
-               Write_BOM => BOM_Present and then Unit_Number /= 1,
+               Write_BOM => BOM /= Unknown,
                Success   => Success);
             exit when not Success;
          end if;
@@ -1608,6 +1606,13 @@ procedure Gnatchop is
             String'Write
               (Stream_IO.Stream (File),
                Source.all (Source'First .. Source'First + BOM_Length - 1));
+
+            --  The BOM is part of the first unit so do not write it twice
+
+            if Num = 1 then
+               Info.Offset := Info.Offset + BOM_Length;
+               Length := Length - BOM_Length;
+            end if;
          end if;
 
          --  Prepend configuration pragmas if necessary