implement `ensureMove` (#22339)

* implement `ensureMove`

* use an additional flag

* improve some logics

* progress: fixes discard ensureMove

* forbids nested expressions

* improve error messages

* checkpoint

* fixes cursor

* ADD MORE TESTS

* fixes cursorinference again

* tiny cleanup

* improve error messages

* fixes docs

* implement comments add more tests

* fixes js

1 files changed, 130 insertions, 0 deletions

diff --git a/tests/system/tensuremove.nim b/tests/system/tensuremove.nim
new file mode 100644
index 000000000..980f2ea58
--- /dev/null
+++ b/tests/system/tensuremove.nim
@@ -0,0 +1,130 @@
+discard """
+  target: "c js"
+  matrix: "--cursorinference:on; --cursorinference:off"
+"""
+
+block:
+  type
+    X = object
+      s: string
+
+  proc `=copy`(x: var X, y: X) =
+    x.s = "copied " & y.s
+
+  proc `=sink`(x: var X, y: X) =
+    `=destroy`(x)
+    wasMoved(x)
+    x.s = "moved " & y.s
+
+  proc consume(x: sink X) =
+    discard x.s
+
+  proc main =
+    var x = X(s: "abcdefg")
+    consume(ensureMove x)
+
+  static: main()
+  main()
+
+block:
+  type
+    String = object
+      id: string
+
+  proc hello =
+    var s = String(id: "1")
+    var m = ensureMove s
+    doAssert m.id == "1"
+
+  hello()
+
+block:
+  type
+    String = object
+      id: string
+
+  proc hello =
+    var n = "1"
+    var s = String(id: ensureMove n)
+    var m = ensureMove s
+    doAssert m.id == "1"
+
+  hello()
+
+block:
+  type
+    String = object
+      id: string
+
+  proc hello =
+    var n = "1"
+    var s = [ensureMove n]
+    var m = ensureMove s
+    doAssert m[0] == "1"
+
+  hello()
+
+block:
+  type
+    String = object
+      id: string
+
+  proc hello =
+    var n = "1"
+    var s = @[ensureMove n]
+    var m = ensureMove s
+    doAssert m[0] == "1"
+
+  hello()
+
+block:
+  type
+    String = object
+      id: string
+
+  proc hello =
+    var s = String(id: "1")
+    var m = ensureMove s.id
+    doAssert m == "1"
+
+  hello()
+
+block:
+  proc foo =
+    var x = 1
+    let y = ensureMove x # move
+    when not defined(js):
+      doAssert (y, x) == (1, 0) # (1, 0)
+  foo()
+
+block:
+  proc foo =
+    var x = 1
+    let y = ensureMove x # move
+    doAssert y == 1
+  foo()
+
+block:
+  proc foo =
+    var x = @[1, 2, 3]
+    let y = ensureMove x[0] # move
+    doAssert y == 1
+    when not defined(js):
+      doAssert x == @[0, 2, 3]
+  foo()
+
+block:
+  proc foo =
+    var x = [1, 2, 3]
+    let y = ensureMove x[0] # move
+    doAssert y == 1
+    when not defined(js):
+      doAssert x == @[0, 2, 3]
+  foo()
+
+block:
+  proc foo =
+    var x = @["1", "2", "3"]
+    let y = ensureMove x[0] # move
+    doAssert y == "1"
+  foo()