join: add tests, correct behavior

+stdlib/join.m

@@ -1,10 +1,40 @@
-function p = join(a, b)
+function p = join(a, b, use_java)
 %% JOIN: join two paths with posix file separator
 arguments
   a (1,1) string
   b (1,1) string
+  use_java (1,1) logical = false
 end
 
-p = stdlib.posix(fullfile(a, b));
+if a == "" && b == ""
+  p = "";
+  return
+end
+
+if a == ""
+  p = b;
+  return
+end
+
+if b == ""
+  p = a;
+  return
+end
+
+
+if use_java
+
+p = stdlib.posix(java.io.File(stdlib.normalize(a, true)).toPath().resolve(stdlib.normalize(b, true)));
+
+else
+
+if stdlib.is_absolute(b)
+  p = b;
+  return
+end
+
+p = stdlib.normalize(a) + "/" + stdlib.normalize(b);
+
+end
 
 end

+stdlib/parent.m

@@ -10,6 +10,7 @@
   % java is about 10x slower than intrinsic
   p = java.io.File(p).getParent();
 else
+  p = stdlib.posix(p);
   % drop duplicated slashes in the parent path
   p = regexprep(p, "//+", "/");
 

test/TestFilePure.m

@@ -20,6 +20,10 @@
 in_parent
 ref_parent
 
+in_join = {"", "a", "", "a/b/", "/", "", "a", "a//", "a/b/../", "a/b", "ab/cd"}
+other_join = {"", "", "b", "c/", "", "/", "b//", "b//", "c/d/../", "c/d", "/ef"}
+ref_join = {"", "a", "b", "a/b/c", "/", "/", "a/b", "a/b", "a/c", "a/b/c/d", "/ef"}
+
 in_suffix = {"", "/foo/bar/baz", "/foo/bar/baz/", "foo/bar/baz.txt", "foo/bar/baz.txt.gz", ".stat", ".stat.txt"}
 ref_suffix = {"", "", "", ".txt", ".gz", ".stat", ".txt"}
 
@@ -166,6 +170,11 @@ function test_posix(tc)
 end
 
 
+function test_join(tc, in_join, other_join, ref_join)
+tc.verifyEqual(stdlib.join(in_join, other_join), ref_join)
+end
+
+
 function test_filename(tc, in_filename, ref_filename)
 tc.verifyEqual(stdlib.filename(in_filename), string(ref_filename))
 end