Realpath symlinks handling, solves issue #3669 (#3703)

tests/by-util/test_cp.rs

@@ -1492,13 +1492,12 @@ fn test_copy_through_just_created_symlink() {
         at.mkdir("a");
         at.mkdir("b");
         at.mkdir("c");
-        #[cfg(unix)]
-        fs::symlink("../t", at.plus("a/1")).unwrap();
-        #[cfg(target_os = "windows")]
-        symlink_file("../t", at.plus("a/1")).unwrap();
+        at.relative_symlink_file("../t", "a/1");
         at.touch("b/1");
+        at.write("b/1", "hello");
         if create_t {
             at.touch("t");
+            at.write("t", "world");
         }
         ucmd.arg("--no-dereference")
             .arg("a/1")
@@ -1510,6 +1509,9 @@ fn test_copy_through_just_created_symlink() {
             } else {
                 "cp: will not copy 'b/1' through just-created symlink 'c\\1'"
             });
+        if create_t {
+            assert_eq!(at.read("a/1"), "world");
+        }
     }
 }
 
@@ -1536,6 +1538,16 @@ fn test_copy_through_dangling_symlink_no_dereference() {
         .no_stdout();
 }
 
+#[test]
+fn test_copy_through_dangling_symlink_no_dereference_2() {
+    let (at, mut ucmd) = at_and_ucmd!();
+    at.touch("file");
+    at.symlink_file("nonexistent", "target");
+    ucmd.args(&["-P", "file", "target"])
+        .fails()
+        .stderr_only("cp: not writing through dangling symlink 'target'");
+}
+
 #[test]
 #[cfg(unix)]
 fn test_cp_archive_on_nonexistent_file() {
@@ -1658,3 +1670,52 @@ fn test_cp_overriding_arguments() {
         s.fixtures.remove("file2");
     }
 }
+
+#[test]
+fn test_copy_no_dereference_1() {
+    let (at, mut ucmd) = at_and_ucmd!();
+    at.mkdir("a");
+    at.mkdir("b");
+    at.touch("a/foo");
+    at.write("a/foo", "bar");
+    at.relative_symlink_file("../a/foo", "b/foo");
+    ucmd.args(&["-P", "a/foo", "b"]).fails();
+}
+
+#[test]
+fn test_abuse_existing() {
+    let (at, mut ucmd) = at_and_ucmd!();
+    at.mkdir("a");
+    at.mkdir("b");
+    at.mkdir("c");
+    at.relative_symlink_file("../t", "a/1");
+    at.touch("b/1");
+    at.write("b/1", "hello");
+    at.relative_symlink_file("../t", "c/1");
+    at.touch("t");
+    at.write("t", "i");
+    ucmd.args(&["-dR", "a/1", "b/1", "c"])
+        .fails()
+        .stderr_contains(format!(
+            "will not copy 'b/1' through just-created symlink 'c{}1'",
+            if cfg!(windows) { "\\" } else { "/" }
+        ));
+    assert_eq!(at.read("t"), "i");
+}
+
+#[test]
+fn test_copy_same_symlink_no_dereference() {
+    let (at, mut ucmd) = at_and_ucmd!();
+    at.relative_symlink_file("t", "a");
+    at.relative_symlink_file("t", "b");
+    at.touch("t");
+    ucmd.args(&["-d", "a", "b"]).succeeds();
+}
+
+#[test]
+fn test_copy_same_symlink_no_dereference_dangling() {
+    let (at, mut ucmd) = at_and_ucmd!();
+    at.relative_symlink_file("t", "a");
+    at.relative_symlink_file("t", "b");
+    ucmd.args(&["-d", "a", "b"]).succeeds();
+}