correct comparisons for nil strings/seqs

compiler/ccgexprs.nim

@@ -980,10 +980,10 @@ proc genEcho(p: BProc, n: PNode) =
     var a: TLoc
     for it in n.sons:
       if it.skipConv.kind == nkNilLit:
-        add(args, ", \"nil\"")
+        add(args, ", \"\"")
       else:
         initLocExpr(p, it, a)
-        addf(args, ", $1? ($1)->data:\"nil\"", [rdLoc(a)])
+        addf(args, ", $1? ($1)->data:\"\"", [rdLoc(a)])
     p.module.includeHeader("<base/log.h>")
     linefmt(p, cpsStmts, """Genode::log(""$1);$n""", args)
   else:
@@ -1755,16 +1755,14 @@ proc genStrEquals(p: BProc, e: PNode, d: var TLoc) =
   var x: TLoc
   var a = e.sons[1]
   var b = e.sons[2]
-  if (a.kind == nkNilLit) or (b.kind == nkNilLit):
-    binaryExpr(p, e, d, "($1 == $2)")
-  elif (a.kind in {nkStrLit..nkTripleStrLit}) and (a.strVal == ""):
+  if a.kind in {nkStrLit..nkTripleStrLit} and a.strVal == "":
     initLocExpr(p, e.sons[2], x)
     putIntoDest(p, d, e,
-      rfmt(nil, "(($1) && ($1)->$2 == 0)", rdLoc(x), lenField(p)))
-  elif (b.kind in {nkStrLit..nkTripleStrLit}) and (b.strVal == ""):
+      rfmt(nil, "(!($1) || ($1)->$2 == 0)", rdLoc(x), lenField(p)))
+  elif b.kind in {nkStrLit..nkTripleStrLit} and b.strVal == "":
     initLocExpr(p, e.sons[1], x)
     putIntoDest(p, d, e,
-      rfmt(nil, "(($1) && ($1)->$2 == 0)", rdLoc(x), lenField(p)))
+      rfmt(nil, "(!($1) || ($1)->$2 == 0)", rdLoc(x), lenField(p)))
   else:
     binaryExpr(p, e, d, "#eqStrings($1, $2)")
 

compiler/condsyms.nim

@@ -82,7 +82,6 @@ proc countDefinedSymbols*(): int =
 
 proc initDefines*() =
   gSymbols = newStringTable(modeStyleInsensitive)
-  defineSymbol("nimrod") # 'nimrod' is always defined
   # for bootstrapping purposes and old code:
   defineSymbol("nimhygiene")
   defineSymbol("niminheritable")
@@ -115,3 +114,4 @@ proc initDefines*() =
   defineSymbol("nimHasNilChecks")
   defineSymbol("nimSymKind")
   defineSymbol("nimVmEqIdent")
+  defineSymbol("nimNoNil")

compiler/vmgen.nim

@@ -1553,6 +1553,7 @@ proc getNullValue(typ: PType, info: TLineInfo): PNode =
     result = newNodeIT(nkFloatLit, info, t)
   of tyCString, tyString:
     result = newNodeIT(nkStrLit, info, t)
+    result.strVal = ""
   of tyVar, tyLent, tyPointer, tyPtr, tySequence, tyExpr,
      tyStmt, tyTypeDesc, tyStatic, tyRef, tyNil:
     result = newNodeIT(nkNilLit, info, t)

lib/impure/nre.nim

@@ -645,7 +645,6 @@ template replaceImpl(str: string, pattern: Regex,
     let bounds = match.matchBounds
     result.add(str.substr(lastIdx, bounds.a - 1))
     let nextVal = replacement
-    assert(nextVal != nil)
     result.add(nextVal)
 
     lastIdx = bounds.b + 1

lib/system.nim

@@ -2412,8 +2412,9 @@ proc `==` *[T](x, y: seq[T]): bool {.noSideEffect.} =
     if seqToPtr(x) == seqToPtr(y):
       return true
 
-  if x.isNil or y.isNil:
-    return false
+  when not defined(nimNoNil):
+    if x.isNil or y.isNil:
+      return false
 
   if x.len != y.len:
     return false
@@ -4010,18 +4011,18 @@ proc addQuoted*[T](s: var string, x: T) =
 
 when hasAlloc:
   # XXX: make these the default (or implement the NilObject optimization)
-  proc safeAdd*[T](x: var seq[T], y: T) {.noSideEffect.} =
+  proc safeAdd*[T](x: var seq[T], y: T) {.noSideEffect, deprecated.} =
     ## Adds ``y`` to ``x`` unless ``x`` is not yet initialized; in that case,
     ## ``x`` becomes ``@[y]``
     if x == nil: x = @[y]
     else: x.add(y)
 
-  proc safeAdd*(x: var string, y: char) =
+  proc safeAdd*(x: var string, y: char) {.noSideEffect, deprecated.} =
     ## Adds ``y`` to ``x``. If ``x`` is ``nil`` it is initialized to ``""``
     if x == nil: x = ""
     x.add(y)
 
-  proc safeAdd*(x: var string, y: string) =
+  proc safeAdd*(x: var string, y: string) {.noSideEffect, deprecated.} =
     ## Adds ``y`` to ``x`` unless ``x`` is not yet initalized; in that
     ## case, ``x`` becomes ``y``
     if x == nil: x = y

lib/system/sysstr.nim

@@ -22,21 +22,34 @@ proc resize(old: int): int {.inline.} =
 
 proc cmpStrings(a, b: NimString): int {.inline, compilerProc.} =
   if a == b: return 0
-  if a == nil: return -1
-  if b == nil: return 1
-  let minlen = min(a.len, b.len)
+  when defined(nimNoNil):
+    let alen = if a == nil: 0 else: a.len
+    let blen = if b == nil: 0 else: b.len
+  else:
+    if a == nil: return -1
+    if b == nil: return 1
+    let alen = a.len
+    let blen = b.len
+  let minlen = min(alen, blen)
   if minlen > 0:
     result = c_memcmp(addr a.data, addr b.data, minlen.csize)
     if result == 0:
-      result = a.len - b.len
+      result = alen - blen
   else:
-    result = a.len - b.len
+    result = alen - blen
 
 proc eqStrings(a, b: NimString): bool {.inline, compilerProc.} =
   if a == b: return true
-  if a == nil or b == nil: return false
-  return a.len == b.len and
-    equalMem(addr(a.data), addr(b.data), a.len)
+  when defined(nimNoNil):
+    let alen = if a == nil: 0 else: a.len
+    let blen = if b == nil: 0 else: b.len
+  else:
+    if a == nil or b == nil: return false
+    let alen = a.len
+    let blen = b.len
+  if alen == blen:
+    if alen == 0: return true
+    return equalMem(addr(a.data), addr(b.data), alen)
 
 when declared(allocAtomic):
   template allocStr(size: untyped): untyped =

tests/system/toString.nim

@@ -51,3 +51,59 @@ import strutils
 let arr = ['H','e','l','l','o',' ','W','o','r','l','d','!','\0']
 doAssert $arr == "['H', 'e', 'l', 'l', 'o', ' ', 'W', 'o', 'r', 'l', 'd', '!', '\\x00']"
 doAssert $cstring(unsafeAddr arr) == "Hello World!"
+
+proc takes(c: cstring) =
+  doAssert c == ""
+
+proc testm() =
+  var x: string
+  # nil is mapped to "":
+  takes(x)
+
+testm()
+
+# nil tests
+var xx: seq[string]
+var yy: string
+doAssert xx == @[]
+doAssert yy == ""
+
+proc bar(arg: cstring): void =
+  doAssert arg[0] == '\0'
+
+proc baz(arg: openarray[char]): void =
+  doAssert arg.len == 0
+
+proc stringCompare(): void =
+  var a,b,c,d,e,f,g: string
+  a.add 'a'
+  doAssert a == "a"
+  b.add "bee"
+  doAssert b == "bee"
+  b.add g
+  doAssert b == "bee"
+  c.add 123.456
+  doAssert c == "123.456"
+  d.add 123456
+  doAssert d == "123456"
+
+  doAssert e == ""
+  doAssert "" == e
+  doAssert nil == e
+  doAssert e == nil
+  doAssert f == g
+  doAssert "" == ""
+  doAssert "" == nil
+  doAssert nil == ""
+
+  g.setLen(10)
+  doAssert g == "\0\0\0\0\0\0\0\0\0\0"
+  doAssert "" != "\0\0\0\0\0\0\0\0\0\0"
+
+  var nilstring: string
+  bar(nilstring)
+  baz(nilstring)
+
+stringCompare()
+static:
+  stringCompare()