names<- retains sorting attributes

NAMESPACE

@@ -106,6 +106,7 @@ S3method(dim, data.table)
 S3method(dimnames, data.table)
 S3method("dimnames<-", data.table)
 S3method("names<-", data.table)
+S3method("colnames<-", data.table)
 S3method(duplicated, data.table)
 S3method(unique, data.table)
 S3method(merge, data.table)

R/data.table.R

@@ -2250,15 +2250,17 @@ dimnames.data.table = function(x) {
   x  # this returned value is now shallow copied by R 3.1.0 via *tmp*. A very welcome change.
 }
 
-"names<-.data.table" = function(x,value)
+"names<-.data.table" = "colnames<-.data.table" = function(x,value)
 {
   # When non data.table aware packages change names, we'd like to maintain the key.
   # If call is names(DT)[2]="newname", R will call this names<-.data.table function (notice no i) with 'value' already prepared to be same length as ncol
-  x = shallow(x) # `names<-` should not modify by reference. Related to #1015, #476 and #825. Needed for R v3.1.0+.  TO DO: revisit
+  x = .shallow(x, retain.key=TRUE) # `names<-` should not modify by reference. Related to #1015, #476 and #825. Needed for R v3.1.0+.  TO DO: revisit
   if (is.null(value))
     setattr(x,"names",NULL)   # e.g. plyr::melt() calls base::unname()
-  else
+  else {
     setnames(x,value)
+    setalloccol(x)
+  }
   x   # this returned value is now shallow copied by R 3.1.0 via *tmp*. A very welcome change.
 }
 

inst/tests/tests.Rraw

@@ -18111,3 +18111,35 @@ test(2238.9, NA %notin% c(1:5, NA), FALSE)
 
 # shift actionable error on matrix input #5287
 test(2239.1, shift(matrix(1:10, ncol = 1)), error="consider wrapping")
+
+# names<- retains index and key, #5125, #5126, #5126, #5128
+DT <- data.table(a = 1, b = 2)
+setkey(DT, a)
+setindex(DT, b)
+names(DT) <- c("c", "d")
+test(2240.1, key(DT), "c")
+test(2240.2, indices(DT), "d")
+
+# Test warnings for names<- and colnames<-, but only warnings when caller is data.table aware.
+DT = data.table(a=1:3, b=4:6, key="a")
+test(2241.01, names(DT)[1]<-"A", "A")
+test(2241.02, DT, data.table(A=1:3, b=4:6, key="A"))  # key wasn't retained in dev after #5084
+test(2241.03, DT[, C:=1], data.table(A=1:3, b=4:6, C=1, key="A"))  # ensure over-allocated ok and no warning
+test(2241.04, set(DT, j="D", value=2), data.table(A=1:3, b=4:6, C=1, D=2, key="A"))  # using set() too
+test(2241.05, colnames(DT)[2]<-"B", "B")
+test(2241.06, DT, data.table(A=1:3, B=4:6, C=1, D=2, key="A"))
+test(2241.07, set(DT, j="E", value=3), data.table(A=1:3, B=4:6, C=1, D=2, E=3, key="A"))
+test(2241.08, names(DT)<-letters[1:5], letters[1:5])  # R doesn't copy *tmp* when assigning to all names 
+test(2241.09, DT, data.table(a=1:3, b=4:6, c=1, d=2, e=3, key="a"))
+test(2241.10, set(DT, j="f", value=4), data.table(a=1:3, b=4:6, c=1, d=2, e=3, f=4, key="a"))
+
+# spotted by @ColeMiller1 in https://github.com/Rdatatable/data.table/pull/5133/files#r1320780851
+DT = data.table(id=1:2, x=1:2)
+r = copy(DT)[, x := 5L]
+test(2241.11, DT, data.table(id=1:2, x=1:2))
+test(2241.12, r, data.table(id=1:2, x=c(5L,5L)))
+
+DT = data.table(id=1:2, x=1:2)
+r = copy(DT)[1L, x:= 5L]
+test(2241.13, DT, data.table(id=1:2, x=1:2))
+test(2241.14, r, data.table(id=1:2, x=c(5L,2L)))