fixes-25655; defining >= operator generates compile error (#25787)

Fixes https://github.com/nim-lang/Nim/issues/25655

---------

Co-authored-by: Andreas Rumpf <araq4k@proton.me>

compiler/lineinfos.nim

@@ -100,6 +100,7 @@ type
     warnGlobalVarConstructorTemporary = "GlobalVarConstructorTemporary",
     warnImplicitRangeConversion = "ImplicitRangeConversion",
     warnSystemRangeConversion = "SystemRangeConversion",
+    warnInvalidCmpOp = "InvalidCmpOp",
     # hints
     hintSuccess = "Success", hintSuccessX = "SuccessX",
     hintCC = "CC",
@@ -210,6 +211,7 @@ const
     warnGlobalVarConstructorTemporary: "global variable '$1' initialization requires a temporary variable",
     warnImplicitRangeConversion: "implicit range conversion $1",
     warnSystemRangeConversion: "implicit range conversion $1",
+    warnInvalidCmpOp: "$1",
     hintSuccess: "operation successful: $#",
     # keep in sync with `testament.isSuccess`
     hintSuccessX: "$build\n$loc lines; ${sec}s; $mem; proj: $project; out: $output",

compiler/nilcheck.nim

@@ -183,12 +183,6 @@ func `<`*(a: ExprIndex, b: ExprIndex): bool =
 func `<=`*(a: ExprIndex, b: ExprIndex): bool =
   a.int16 <= b.int16
 
-func `>`*(a: ExprIndex, b: ExprIndex): bool =
-  a.int16 > b.int16
-
-func `>=`*(a: ExprIndex, b: ExprIndex): bool =
-  a.int16 >= b.int16
-
 func `==`*(a: ExprIndex, b: ExprIndex): bool =
   a.int16 == b.int16
 

compiler/semstmts.nim

@@ -2642,6 +2642,11 @@ proc semProcAux(c: PContext, n: PNode, kind: TSymKind,
       elif s.name.s == "()" and callOperator notin c.features:
         localError(c.config, n.info, "the overloaded " & s.name.s &
           " operator has to be enabled with {.experimental: \"callOperator\".}")
+    elif sfImportc notin s.flags and (s.name.s == ">" or s.name.s == ">=" or s.name.s == "!="):
+      # ignore imported procs as these operators in backend language might have different semantics
+      let op1 = if s.name.s == "!=": "==" elif s.name.s == ">": "<" else: "<="
+      message(c.config, n.info, warnInvalidCmpOp, "define `" & op1 & "` instead of `" & s.name.s & "` to implement user defined comparison operator. " &
+              "it allows you to use `" & s.name.s & "` automatically.")
 
   if sfBorrow in s.flags and c.config.cmd notin cmdDocLike:
     result[bodyPos] = c.graph.emptyNode