# SlicerRT extension build failure

**URL:** <https://discourse.slicer.org/t/slicerrt-extension-build-failure/3010>\
**Category:** Development\
**Created:** [May 29, 2018, 6:40pm UTC](https://discourse.slicer.org/t/slicerrt-extension-build-failure/3010 "2018-05-29T18:40:50Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![gcsharp](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/gcsharp/32/863_2.png) [@gcsharp](https://discourse.slicer.org/u/gcsharp)\
**Post date:** [May 29, 2018, 6:40pm UTC](https://discourse.slicer.org/t/slicerrt-extension-build-failure/3010/1 "2018-05-29T18:40:50Z")

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Any idea why this is happening?

```
    -- SuperBuild - First pass - done
    -- SuperBuild - inner => Requires Plastimatch, 
    -- SuperBuild - Plastimatch[OK]
    CMake Error at SuperBuild/External_Plastimatch.cmake:46 (ExternalProject_Add):
      Unknown CMake command "ExternalProject_Add".
    Call Stack (most recent call first):
      /home/kitware/Dashboards/Package/Slicer-481/CMake/ExternalProjectDependency.cmake:683 (include)
      /home/kitware/Dashboards/Package/Slicer-481/CMake/ExternalProjectDependency.cmake:746 (ExternalProject_Include_Dependencies)
      SuperBuild.cmake:24 (ExternalProject_Include_Dependencies)
      CMakeLists.txt:43 (include)

```

[http://slicer.cdash.org/buildSummary.php?buildid=1282802](http://slicer.cdash.org/buildSummary.php?buildid=1282802)

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**Author:** ![lassoan](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/lassoan/32/13_2.png) [@lassoan](https://discourse.slicer.org/u/lassoan)\
**Post date:** [May 29, 2018, 6:53pm UTC](https://discourse.slicer.org/t/slicerrt-extension-build-failure/3010/2 "2018-05-29T18:53:23Z")

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Probably `include(ExternalProject)` is missed.

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<div class="post-metadata">

**Author:** ![gcsharp](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/gcsharp/32/863_2.png) [@gcsharp](https://discourse.slicer.org/u/gcsharp)\
**Post date:** [May 29, 2018, 7:06pm UTC](https://discourse.slicer.org/t/slicerrt-extension-build-failure/3010/3 "2018-05-29T19:06:13Z")

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Yes, that is what a topic on Stack Exchange suggests. It is easy and harmless to add. But I have doubts on effectiveness because it was apparently never needed before, and when I build it locally, I don’t get this error.

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**Author:** ![jcfr](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/jcfr/32/17825_2.png) [@jcfr](https://discourse.slicer.org/u/jcfr)\
**Post date:** [May 29, 2018, 11:49pm UTC](https://discourse.slicer.org/t/slicerrt-extension-build-failure/3010/4 "2018-05-29T23:49:04Z")

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Explicitly including the ExternalProject module is only required with Slicer 4.8.1. Since [r26984](http://viewvc.slicer.org/viewvc.cgi/Slicer4?view=revision&revision=26984) it is included through `UseSlicer.cmake`. This is why it was removed in [SlicerRt/SlicerRT@6495332](https://github.com/SlicerRt/SlicerRT/commit/6495332b380437e4f525018a47842f457afc791f#diff-88b37dcc9267d819b6fabff68a8e5290)

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<div class="post-metadata">

**Author:** ![gcsharp](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/gcsharp/32/863_2.png) [@gcsharp](https://discourse.slicer.org/u/gcsharp)\
**Post date:** [May 30, 2018, 3:17pm UTC](https://discourse.slicer.org/t/slicerrt-extension-build-failure/3010/5 "2018-05-30T15:17:04Z")

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It seems the s4ext points to an older version. Could someone please update when you get a chance? Thanks!

> <https://github.com/Slicer/ExtensionsIndex/pull/1552>
>
> …ernalProjectDependency