add .sf_namespace attribute by default

closes #2277
closes #2212

NEWS.md

@@ -1,5 +1,7 @@
 # version 1.0-16
 
+* unless the env. variable `ADD_SF_NAMESPACE` is set to `false`, `sf` objects contain an attribute, `.sf_namespace`, which forces loading the `sf` namespace when it has not been loaded so far, e.g. for printing or plotting of an `sf` object; #2212 by Mike Mahoney
+
 * `st_sample()` works when unprojected polygon geometry crosses the antemeridian; #2331
 
 * clean up and modernization of S3 registration of methods and tests; #2285, #2288, #2316, #2341, #2342, by @olivroy

R/sf.R

@@ -299,7 +299,7 @@ st_sf = function(..., agr = NA_agr_, row.names,
 	if (! missing(crs))
 		st_crs(df) = crs
 
-	if (Sys.getenv("ADD_SF_NAMESPACE") == "true")
+	if (Sys.getenv("ADD_SF_NAMESPACE") != "false")
 		attr(df, ".sf_namespace") <- .sf_namespace
 
 	df

tests/sfc.Rout.save

@@ -347,7 +347,7 @@ use `st_zm(...)` to coerce to XY dimensions
 > 
 > sf_extSoftVersion()[1:3]
     GEOS     GDAL   proj.4 
-"3.12.1"  "3.8.3"  "9.3.1" 
+"3.12.1"  "3.8.4"  "9.3.1" 
 > 
 > # Ops.sfc:
 > ls = st_sfc(st_linestring(rbind(c(0,0),c(0,1))))
@@ -437,6 +437,7 @@ Classes 'sf' and 'data.frame':	100 obs. of  15 variables:
  - attr(*, "sf_column")= chr "geometry"
  - attr(*, "agr")= Factor w/ 3 levels "constant","aggregate",..: NA NA NA NA NA NA NA NA NA NA ...
   ..- attr(*, "names")= chr [1:14] "AREA" "PERIMETER" "CNTY_" "CNTY_ID" ...
+ - attr(*, ".sf_namespace")=function ()  
 > bb = st_as_sfc(st_bbox(nc))
 > format(st_bbox(nc))
 [1] "((-84.32385,33.88199),(-75.45698,36.58965))"
@@ -1088,4 +1089,4 @@ CRS:           NA
 > 
 > proc.time()
    user  system elapsed 
-  5.127   1.392   5.019 
+  5.159   1.424   5.082