Provide backtrace to the point in template where a function gets called over "nil"

[kaushalmodi]

Reference: https://discourse.gohugo.io/t/runtime-error-invalid-memory-address-or-nil-pointer-dereference/11881/12?u=kaushalmodi

An example problematic template snippet:

{{ (.Site.GetPage "taxonomyTerm" "categories" "foo").Permalink }}

Now if that (.Site.GetPage "taxonomyTerm" "categories" "foo") returns nil, hugo would only print something like:

Building sites … ERROR 2018/05/08 14:55:46 Failed to render "theme/index.html": runtime error: invalid memory address or nil pointer dereference

That error does not mean that the referenced index.html has the problematic statement.. the error could be in any of the nested partials in that file. So the debug becomes time-consuming as you comment/uncomment the template files in halves to narrow down to the actual buggy line in the template.

[regisphilibert]

This indeed would shorten many debugging situations. I've got a tiny tear in my eyes now when I see this dreaded error.

[moorereason]

I'm unable to reproduce this issue now. Can anyone confirm?

I have an old v0.54.0 binary, and it shows better results even back then. Not sure what version of Go I used to compile it, though (PS - maybe we should output the Go runtime version in our hugo version output).

Here's the changes I tested against the gohugoioTheme:

diff --git a/themes/gohugoioTheme/layouts/partials/home-page-sections/features-icons.html b/themes/gohugoioTheme/layouts/partials/home-page-sections/features-icons.html
index a7733acdc..239a5a57e 100644
--- a/themes/gohugoioTheme/layouts/partials/home-page-sections/features-icons.html
+++ b/themes/gohugoioTheme/layouts/partials/home-page-sections/features-icons.html
@@ -5,6 +5,7 @@
       {{ range $i, $e := $features  }}
         {{ $features_count := $e | len }}

+        {{ ($.Site.GetPage "foo").Permalink }}
         <div class="w-100{{ if and (eq $i $features_count) (ne (modBool $features_count 2) true) }} w-70-ns {{ else }} w-50-ns {{ end }}ph5-l pv5-l nested-copy-line-height">
           <!-- NOTE:  "if eq $i $features_count" makes the last item a bit wider for balance. If we use an even number of items, we'll want to remove this -->
           <div class="flex-l flex-wrap justify-between">

Output:

Error: Error building site: failed to render pages: render of "home" failed: "/hugoDocs/themes/gohugoioTheme/layouts/index.html:8:33": execute of template failed: template
: index.html:8:8: executing "main" at <partial "home-page-sections/features-icons" .>: error calling partial: "/hugoDocs/themes/gohugoioTheme/layouts/partials/home-page-se
ctions/features-icons.html:8:33": execute of template failed: template: partials/home-page-sections/features-icons.html:8:33: executing "partials/home-page-sections/features-icons.html" at <($.Site.GetPage "
foo").Permalink>: error calling Permalink: runtime error: invalid memory address or nil pointer dereference

[bep]

@moorereason this is fixed.

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