metrics: Detect partialCached candidates

This commit adds a "cache potential" column when running `hugo --templateMetrics --templateMetricsHints`.

This is only calculated when `--templateMetricsHints` is set, as these calculations has an negative effect on the other timings.

This gives a value for partials only, and is a number between 0-100 that indicates if `partial` can be replaced with `partialCached`.

100 means that all execution of the same partial resulted in the same output.

You should do  some manual research before going "all cache".

1 files changed, 10 insertions, 2 deletions

diff --git a/tpl/partials/partials.go b/tpl/partials/partials.go
index da131a974..d3a75edad 100644
--- a/tpl/partials/partials.go
+++ b/tpl/partials/partials.go
@@ -77,10 +77,18 @@ func (ns *Namespace) Include(name string, contextList ...interface{}) (interface
 			}
 
 			if _, ok := templ.Template.(*texttemplate.Template); ok {
-				return b.String(), nil
+				s := b.String()
+				if ns.deps.Metrics != nil {
+					ns.deps.Metrics.TrackValue(n, s)
+				}
+				return s, nil
 			}
 
-			return template.HTML(b.String()), nil
+			s := b.String()
+			if ns.deps.Metrics != nil {
+				ns.deps.Metrics.TrackValue(n, s)
+			}
+			return template.HTML(s), nil
 
 		}
 	}