fixes #17173 (#17213)

* fixes #17173

* add testcase (#17214)

* Apply suggestions from code review

* fix for newruntime

* Apply suggestions from code review

* Update lib/system.nim

* Update lib/system.nim

* Update lib/system.nim

Co-authored-by: Danil Yarantsev <tiberiumk12@gmail.com>

Co-authored-by: flywind <xzsflywind@gmail.com>
Co-authored-by: Danil Yarantsev <tiberiumk12@gmail.com>

changelog.md

@@ -173,6 +173,12 @@ provided by the operating system.
   dumping (on select signals) and notifying the parent process about the cause
   of termination.
 
+- Added `system.prepareStrMutation` for better support of low
+  level `moveMem`, `copyMem` operations for Orc's copy-on-write string
+  implementation.
+
+- `hashes.hash` now supports `object`, but can be overloaded.
+
 - Added `std/strbasics` for high performance string operations.
   Added `strip`, `setSlice`, `add(a: var string, b: openArray[char])`.
 

lib/std/strbasics.nim

@@ -80,6 +80,8 @@ func setSlice*(s: var string, slice: Slice[int]) =
       when not declared(moveMem):
         impl()
       else:
+        when defined(nimSeqsV2):
+          prepareStrMutation(s)
         moveMem(addr s[0], addr s[first], last - first + 1)
   s.setLen(last - first + 1)
 

lib/system.nim

@@ -3127,3 +3127,9 @@ export io
 
 when not defined(createNimHcr) and not defined(nimscript):
   include nimhcr
+
+when notJSnotNims and not defined(nimSeqsV2):
+  proc prepareStrMutation*(s: var string) {.inline.} =
+    ## String literals (e.g. "abc", etc) in the ARC/ORC mode are "copy on write",
+    ## therefore you should call `prepareStrMutation` before modifying the strings.
+    discard

lib/system/strs_v2.nim

@@ -168,3 +168,10 @@ proc nimPrepareStrMutationImpl(s: var NimStringV2) =
 proc nimPrepareStrMutationV2(s: var NimStringV2) {.compilerRtl, inline.} =
   if s.p != nil and (s.p.cap and strlitFlag) == strlitFlag:
     nimPrepareStrMutationImpl(s)
+
+proc prepareStrMutation*(s: var string) {.inline.} =
+  # string literals are "copy on write", so you need to call
+  # `prepareStrMutation` before modifying the strings.
+  {.cast(noSideEffect).}:
+    let s = unsafeAddr s
+    nimPrepareStrMutationV2(cast[ptr NimStringV2](s)[])

tests/arc/t17173.nim

@@ -0,0 +1,10 @@
+discard """
+  matrix: "--gc:refc; --gc:arc; --newruntime"
+"""
+
+import std/strbasics
+
+
+var a = "  vhellov   "
+strip(a)
+doAssert a == "vhellov"