What happens in Inno Setup when you list the same

What happens when you setup an Inno Setup .iss file to install the same file to the same location twice? Does Inno Setup realize what you are doing, and just include and install the file once, or does it collect the file into the install multiple times, and overwrite it for each instance?

Inno Setup is smart enough to identify an identical source file and will include it only once to the installer. There's a legitimate reason for having duplicate source files; you may want to install the same file to different locations on the target system.

What Inno Setup won't identify is an identical target location (I cannot think of a legitimate reason for having identical target location). So it will install the file twice. Obviously as it installs it twice to an identical location, the second installation actually does not happen (with executable files with the default flags, as the version match) or is barely noticeable (as you overwrite an identical data file).

[Files]
Source: "MyProg.exe"; DestDir: "{app}"
Source: "MyProg.exe"; DestDir: "{app}"
Source: "Requirements.txt"; DestDir: "{app}"
Source: "Requirements.txt"; DestDir: "{app}"

2015-04-01 17:33:06.529   -- File entry --
2015-04-01 17:33:06.529   Dest filename: C:\Program Files (x86)\My Program\MyProg.exe
2015-04-01 17:33:06.529   Time stamp of our file: 2013-08-27 02:00:00.000
2015-04-01 17:33:06.529   Installing the file.
2015-04-01 17:33:06.542   Successfully installed the file.
2015-04-01 17:33:06.543   -- File entry --
2015-04-01 17:33:06.543   Dest filename: C:\Program Files (x86)\My Program\MyProg.exe
2015-04-01 17:33:06.543   Time stamp of our file: 2013-08-27 02:00:00.000
2015-04-01 17:33:06.543   Dest file exists.
2015-04-01 17:33:06.543   Time stamp of existing file: 2013-08-27 02:00:00.000
2015-04-01 17:33:06.543   Version of our file: 1.5.0.0
2015-04-01 17:33:06.545   Version of existing file: 1.5.0.0
2015-04-01 17:33:06.545   Same version. Skipping.
2015-04-01 17:33:06.545   -- File entry --
2015-04-01 17:33:06.545   Dest filename: C:\Program Files (x86)\My Program\Requirements.txt
2015-04-01 17:33:06.546   Time stamp of our file: 2015-04-01 17:29:10.000
2015-04-01 17:33:06.546   Installing the file.
2015-04-01 17:33:06.547   Successfully installed the file.
2015-04-01 17:33:06.547   -- File entry --
2015-04-01 17:33:06.547   Dest filename: C:\Program Files (x86)\My Program\Requirements.txt
2015-04-01 17:33:06.548   Time stamp of our file: 2015-04-01 17:29:10.000
2015-04-01 17:33:06.548   Dest file exists.
2015-04-01 17:33:06.548   Time stamp of existing file: 2015-04-01 17:29:10.000
2015-04-01 17:33:06.548   Version of our file: (none)
2015-04-01 17:33:06.549   Version of existing file: (none)
2015-04-01 17:33:06.549   Installing the file.
2015-04-01 17:33:06.550   Successfully installed the file.