[MacPorts] #60654: Provide Tcl command for manipulating plists

[MacPorts]

#60654: Provide Tcl command for manipulating plists
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 Reporter:  ryandesign   |      Owner:  (none)
     Type:  enhancement  |     Status:  new
 Priority:  Normal       |  Milestone:  MacPorts Future
Component:  ports        |    Version:  2.6.2
 Keywords:               |       Port:
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 plist files are everywhere on macOS. Two specific plists that MacPorts
 needs to deal with frequently are launchd plists (in portstartupitem.tcl)
 and Info plists (in the app 1.0 portgroup). In both cases, the plists are
 constructed manually with string concatenation. This is cumbersome and
 error prone. In addition, some ports desire to augment the plists that
 MacPorts has generated and currently have to resort to convoluted string
 manipulation to do this, or forgo the MacPorts-generated plists entirely
 and provide their own replacement.

 MacPorts should provide a Tcl command for manipulating plists. This could
 be a simple wrapper that just calls an existing executable. Two candidate
 executables are `PlistBuddy` and `plutil`. Some ports already use one;
 some already use the other.

 PlistBuddy has the advantage that it exists on all versions of macOS that
 MacPorts runs on and its syntax allows complex plist modifications. It is
 at /usr/libexec/PlistBuddy on 10.5 and later. It is not installed in a
 standard location on 10.4 but it is present in several installer receipts
 and MacPorts could find it there when needed.

 plutil is installed at /usr/bin/plutil since 10.2 but the `-insert`,
 `-replace` and `-remove` commands that would be most interesting to us
 didn't appear until 10.9.

 Another option is that MacPorts could implement its own plist modification
 functionality directly in Tcl. This would avoid the need to call out to
 another executable, which might be a significant performance gain if we
 consider that the command may need to be invoked dozens of times to build
 up a single plist, and would avoid the problems of either locating
 PlistBuddy on 10.4 or dealing with plutil's deficiencies prior to 10.9. To
 avoid having to write the plist to disk between every invocation, we might
 even consider an API where a plist could be read into memory, then
 successive commands could modify that in-memory representation, and
 finally it could be written out again.

 Whatever we implement, the existing code that creates plists could be
 rewritten to use the new method. This might make that code easier to read
 and modify in the future.

 Providing a generic plist modification facility might reduce the need to
 offer an ever growing set of options specific to either the launchd or
 Info plists.

-- 
Ticket URL: <https://trac.macports.org/ticket/60654>
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