Trac #31409: Make it possible to disable build of r, rpy2 using ./configure --disable-r

Prompted by a build failure of `r` on `cygwin-standard` in
https://github.com/mkoeppe/sage/runs/1915093157
{{{
  [r-3.6.3]   blas.o: in function `dsymm_':
  [r-3.6.3]   /opt/sage-1e693c9ae51a53dad0fe099efc41439dc898f02f/var/tmp
/sage/build/r-3.6.3/src/src/extra/blas/blas.f:2986:(.text+0x4352):
relocation truncated to fit: R_X86_64_PC32 against undefined symbol
`xerbla_'
}}}
we make it possible to disable R using a configure options so that one
can get a working Sage installation in this way.

(The original build failure has hopefully resolved been resolved by
#29537.)

Previous tickets and discussions:
- #29486
- #29441
- #29170
- ​https://groups.google.com/g/sage-devel/c/IX3niEdmCEM/m/LovmF6gmIwAJ
- https://wiki.sagemath.org/ReleaseTours/sage-9.2#rpy2_and_R
- https://groups.google.com/g/sage-devel/c/alkG4veIsBk/m/432cxzpYAQAJ

URL: https://trac.sagemath.org/31409
Reported by: mkoeppe
Ticket author(s): Matthias Koeppe
Reviewer(s): François Bissey, John Palmieri

Author: Release Manager

configure.ac

@@ -424,6 +424,14 @@ AC_ARG_ENABLE([notebook],
     done
   ])
 
+AC_ARG_ENABLE([r],
+  AS_HELP_STRING([--disable-r],
+                 [disable build of the R package and related packages]), [
+    for pkg in r rpy2 r_jupyter; do
+      AS_VAR_SET([SAGE_ENABLE_$pkg], [$enableval])
+    done
+  ])
+
 SAGE_SPKG_COLLECT()
 
 dnl AC_CONFIG_HEADERS([config.h])

src/doc/en/prep/Quickstarts/Statistics-and-Distributions.rst

@@ -146,12 +146,13 @@ the examples in ``r.kruskal_test?`` in the notebook.
 
 ::
 
-    sage: x=r([2.9, 3.0, 2.5, 2.6, 3.2]) # normal subjects
-    sage: y=r([3.8, 2.7, 4.0, 2.4])      # with obstructive airway disease
-    sage: z=r([2.8, 3.4, 3.7, 2.2, 2.0]) # with asbestosis
-    sage: a = r([x,y,z]) # make a long R vector of all the data
-    sage: b = r.factor(5*[1]+4*[2]+5*[3]) # create something for R to tell which subjects are which
-    sage: a; b # show them
+    sage: x=r([2.9, 3.0, 2.5, 2.6, 3.2])  # normal subjects                       # optional - rpy2
+    sage: y=r([3.8, 2.7, 4.0, 2.4])       # with obstructive airway disease       # optional - rpy2
+    sage: z=r([2.8, 3.4, 3.7, 2.2, 2.0])  # with asbestosis                       # optional - rpy2
+    sage: a = r([x,y,z])                  # make a long R vector of all the data  # optional - rpy2
+    sage: b = r.factor(5*[1]+4*[2]+5*[3]) # create something for R to tell        # optional - rpy2
+    ....:                                 #   which subjects are which
+    sage: a; b                            # show them                             # optional - rpy2
      [1] 2.9 3.0 2.5 2.6 3.2 3.8 2.7 4.0 2.4 2.8 3.4 3.7 2.2 2.0
      [1] 1 1 1 1 1 2 2 2 2 3 3 3 3 3
     Levels: 1 2 3
@@ -160,7 +161,7 @@ the examples in ``r.kruskal_test?`` in the notebook.
 
 ::
 
-    sage: r.kruskal_test(a,b) # do the KW test!
+    sage: r.kruskal_test(a,b)             # do the KW test!                       # optional - rpy2
         Kruskal-Wallis rank sum test
 
     data:  sage17 and sage33
@@ -178,7 +179,7 @@ Notice that R also uses the ``#`` symbol to indicate comments.
 
 ::
 
-    sage: %r
+    sage: %r                                                                      # optional - rpy2
     ....: x = c(18,23,25,35,65,54,34,56,72,19,23,42,18,39,37) # ages of individuals
     ....: y = c(202,186,187,180,156,169,174,172,153,199,193,174,198,183,178) # maximum heart rate of each one
     ....: png() # turn on plotting

src/sage/interfaces/interface.py

@@ -798,9 +798,9 @@ def __reduce__(self):
             "abc"
             sage: loads(dumps(pari([1,2,3])))
             [1, 2, 3]
-            sage: loads(dumps(r('"abc"')))
+            sage: loads(dumps(r('"abc"')))                                        # optional - rpy2
             [1] "abc"
-            sage: loads(dumps(r([1,2,3])))
+            sage: loads(dumps(r([1,2,3])))                                        # optional - rpy2
             [1] 1 2 3
             sage: loads(dumps(maxima([1,2,3])))
             [1,2,3]
@@ -851,10 +851,11 @@ def _reduce(self):
         by the doctests because the original identifier was reused. This test makes sure
         that does not happen again:
 
-            sage: a = r("'abc'")
-            sage: b = dumps(a)
-            sage: r.set(a.name(), 0) # make identifier reuse doesn't accidentally lead to success
-            sage: loads(b)
+            sage: a = r("'abc'")                                                  # optional - rpy2
+            sage: b = dumps(a)                                                    # optional - rpy2
+            sage: r.set(a.name(), 0) # make sure that identifier reuse            # optional - rpy2
+            ....:                    # does not accidentally lead to success
+            sage: loads(b)                                                        # optional - rpy2
             [1] "abc"
 
         """
@@ -1376,13 +1377,13 @@ def name(self, new_name=None):
 
         EXAMPLES::
 
-            sage: x = r([1,2,3]); x
+            sage: x = r([1,2,3]); x                                               # optional - rpy2
             [1] 1 2 3
-            sage: x.name()
+            sage: x.name()                                                        # optional - rpy2
             'sage...'
-            sage: x = r([1,2,3]).name('x'); x
+            sage: x = r([1,2,3]).name('x'); x                                     # optional - rpy2
             [1] 1 2 3
-            sage: x.name()
+            sage: x.name()                                                        # optional - rpy2
             'x'
 
         ::