Description: Reproducible builds requires that the build time stamp is not

 recorded in binaries. In FPC they are fuild in via the $INCLUDE %DATE%

 directive which calls getdatestr in globals.pas. To allow reproducible builds

 we should honor the SOURCE_DATE_EPOCH environment variable. To not depend on

 the dateutil unit, we include the required code from that package here.

Author: Paul Gevers <elbrus@debian.org>

Author: Abou Al Montacir <abou.almontacir@sfr.fr>

Index: fpc/fpcsrc/compiler/globals.pas

===================================================================

--- fpc.orig/fpcsrc/compiler/globals.pas

+++ fpc/fpcsrc/compiler/globals.pas

@@ -510,6 +510,7 @@ interface

       starttime  : real;

     function getdatestr:string;

+    Function UnixToDateTime(const AValue: Int64): TDateTime;

     function gettimestr:string;

     function filetimestring( t : longint) : string;

     function getrealtime : real;

@@ -766,11 +767,29 @@ implementation

    }

       var

         Year,Month,Day: Word;

+        SourceDateEpoch: string;

       begin

-        DecodeDate(Date,year,month,day);

+        SourceDateEpoch := GetEnvironmentVariable('SOURCE_DATE_EPOCH');

+        if Length(SourceDateEpoch)>0 then

+           DecodeDate(UnixToDateTime(StrToInt64(SourceDateEpoch)),year,month,day)

+        else

+          DecodeDate(Date,year,month,day);

         getdatestr:=L0(Year)+'/'+L0(Month)+'/'+L0(Day);

       end;

+   Function UnixToDateTime(const AValue: Int64): TDateTime;

+   { Code copied from fpcsrc/packages/rtl-objpas/src/inc/dateutil.inc and

+   fpcsrc/rtl/objpas/sysutils/datih.inc }

+   const

+      TDateTimeEpsilon = 2.2204460493e-16 ;

+      UnixEpoch = TDateTime(-2415018.5) + TDateTime(2440587.5) ;

+   begin

+      Result:=UnixEpoch + AValue/SecsPerDay;

+      if (UnixEpoch>=0) and (Result<-TDateTimeEpsilon) then

+         Result:=int(Result-1.0+TDateTimeEpsilon)-frac(1.0+frac(Result))

+      else if (UnixEpoch<=-1.0) and (Result>-1.0+TDateTimeEpsilon) then

+         Result:=int(Result+1.0-TDateTimeEpsilon)+frac(1.0-abs(frac(1.0+Result)));

+   end;

    function  filetimestring( t : longint) : string;

    {