Deprecate asm stmt for js target (#23149)

why ?

- We already have an emit that does the same thing
- The name asm itself is a bit confusing, you might think it's an alias
for asm.js or something else.
- The asm keyword is used differently on different compiler targets (it
makes it inexpressive).
- Does anyone (other than some compiler libraries) use asm instead of
emit ? If yes, it's a bit strange to use asm somewhere and emit
somewhere. By making the asm keyword for js target deprecated, there
would be even less use of the asm keyword for js target, reducing the
amount of confusion.
- New users might accidentally use a non-universal approach via the asm
keyword instead of emit, and then when they learn about asm, try to
figure out what the differences are.

see https://forum.nim-lang.org/t/10821

---------

Co-authored-by: Andreas Rumpf <rumpf_a@web.de>

compiler/jsgen.nim

@@ -1136,10 +1136,14 @@ proc genBreakStmt(p: PProc, n: PNode) =
   p.blocks[idx].id = abs(p.blocks[idx].id) # label is used
   lineF(p, "break Label$1;$n", [rope(p.blocks[idx].id)])
 
-proc genAsmOrEmitStmt(p: PProc, n: PNode) =
+proc genAsmOrEmitStmt(p: PProc, n: PNode; isAsmStmt = false) =
   genLineDir(p, n)
   p.body.add p.indentLine("")
-  for i in 0..<n.len:
+  let offset =
+    if isAsmStmt: 1 # first son is pragmas
+    else: 0
+
+  for i in offset..<n.len:
     let it = n[i]
     case it.kind
     of nkStrLit..nkTripleStrLit:
@@ -2981,7 +2985,9 @@ proc gen(p: PProc, n: PNode, r: var TCompRes) =
       genLineDir(p, n)
       gen(p, n[0], r)
       r.res = "var _ = " & r.res
-  of nkAsmStmt: genAsmOrEmitStmt(p, n)
+  of nkAsmStmt:
+    warningDeprecated(p.config, n.info, "'asm' for the JS target is deprecated, use the 'emit' pragma")
+    genAsmOrEmitStmt(p, n, true)
   of nkTryStmt, nkHiddenTryStmt: genTry(p, n, r)
   of nkRaiseStmt: genRaiseStmt(p, n)
   of nkTypeSection, nkCommentStmt, nkIncludeStmt,

lib/js/asyncjs.nim

@@ -243,7 +243,7 @@ since (1, 5, 1):
     else:
       type A = impl(onSuccess(default(T)))
     var ret: A
-    asm "`ret` = `future`.then(`onSuccess`, `onReject`)"
+    {.emit: "`ret` = `future`.then(`onSuccess`, `onReject`)".}
     return ret
 
   proc catch*[T](future: Future[T], onReject: OnReject): Future[void] =
@@ -266,4 +266,4 @@ since (1, 5, 1):
 
       discard main()
 
-    asm "`result` = `future`.catch(`onReject`)"
+    {.emit: "`result` = `future`.catch(`onReject`)".}

lib/js/jsre.nim

@@ -58,7 +58,7 @@ func contains*(pattern: cstring; self: RegExp): bool =
     assert jsregex in r"abc"
     assert jsregex notin r"abcd"
     assert "xabc".contains jsregex
-  asm "`result` = `self`.test(`pattern`);"
+  {.emit: "`result` = `self`.test(`pattern`);".}
 
 func startsWith*(pattern: cstring; self: RegExp): bool =
   ## Tests if string starts with given RegExp

lib/pure/hashes.nim

@@ -190,7 +190,7 @@ proc hashData*(data: pointer, size: int): Hash =
   var h: Hash = 0
   when defined(js):
     var p: cstring
-    asm """`p` = `Data`"""
+    {.emit: """`p` = `Data`""".}
   else:
     var p = cast[cstring](data)
   var i = 0
@@ -217,7 +217,7 @@ else:
 when defined(js):
   var objectID = 0
   proc getObjectId(x: pointer): int =
-    asm """
+    {.emit: """
       if (typeof `x` == "object") {
         if ("_NimID" in `x`)
           `result` = `x`["_NimID"];
@@ -226,7 +226,7 @@ when defined(js):
           `x`["_NimID"] = `result`;
         }
       }
-    """
+    """.}
 
 proc hash*(x: pointer): Hash {.inline.} =
   ## Efficient `hash` overload.

lib/pure/json.nim

@@ -991,9 +991,9 @@ when defined(js):
     else: assert false
 
   proc len(x: JsObject): int =
-    asm """
+    {.emit: """
       `result` = `x`.length;
-    """
+    """.}
 
   proc convertObject(x: JsObject): JsonNode =
     var isRawNumber = false
@@ -1004,14 +1004,15 @@ when defined(js):
         result.add(x[i].convertObject())
     of JObject:
       result = newJObject()
-      asm """for (var property in `x`) {
+      {.emit: """for (var property in `x`) {
         if (`x`.hasOwnProperty(property)) {
-      """
+      """.}
+
       var nimProperty: cstring
       var nimValue: JsObject
-      asm "`nimProperty` = property; `nimValue` = `x`[property];"
+      {.emit: "`nimProperty` = property; `nimValue` = `x`[property];".}
       result[$nimProperty] = nimValue.convertObject()
-      asm "}}"
+      {.emit: "}}".}
     of JInt:
       result = newJInt(x.to(int))
     of JFloat:

lib/pure/math.nim

@@ -219,13 +219,13 @@ when defined(js):
     let a = newFloat64Array(buffer)
     let b = newUint32Array(buffer)
     a[0] = x
-    asm """
+    {.emit: """
     function updateBit(num, bitPos, bitVal) {
       return (num & ~(1 << bitPos)) | (bitVal << bitPos);
     }
     `b`[1] = updateBit(`b`[1], 31, `sgn`);
     `result` = `a`[0]
-    """
+    """.}
 
 proc signbit*(x: SomeFloat): bool {.inline, since: (1, 5, 1).} =
   ## Returns true if `x` is negative, false otherwise.

lib/std/exitprocs.nim

@@ -29,13 +29,13 @@ initLock(gFunsLock)
 when defined(js):
   proc addAtExit(quitProc: proc() {.noconv.}) =
     when defined(nodejs):
-      asm """
+      {.emit: """
         process.on('exit', `quitProc`);
-      """
+      """.}
     elif defined(js):
-      asm """
+      {.emit: """
         window.onbeforeunload = `quitProc`;
-      """
+      """.}
 else:
   proc addAtExit(quitProc: proc() {.noconv.}) {.
     importc: "atexit", header: "<stdlib.h>".}
@@ -72,16 +72,16 @@ proc addExitProc*(cl: proc() {.noconv.}) =
 when not defined(nimscript) and (not defined(js) or defined(nodejs)):
   proc getProgramResult*(): int =
     when defined(js) and defined(nodejs):
-      asm """
+      {.emit: """
 `result` = process.exitCode;
-"""
+""".}
     else:
       result = programResult
 
   proc setProgramResult*(a: int) =
     when defined(js) and defined(nodejs):
-      asm """
+      {.emit: """
 process.exitCode = `a`;
-"""
+""".}
     else:
       programResult = a

lib/std/formatfloat.nim

@@ -104,7 +104,7 @@ when defined(js):
   proc nimFloatToString(a: float): cstring =
     ## ensures the result doesn't print like an integer, i.e. return 2.0, not 2
     # print `-0.0` properly
-    asm """
+    {.emit: """
       function nimOnlyDigitsOrMinus(n) {
         return n.toString().match(/^-?\d+$/);
       }
@@ -116,7 +116,7 @@ when defined(js):
           `result` = `a`+".0"
         }
       }
-    """
+    """.}
 
 proc addFloat*(result: var string; x: float | float32) {.inline.} =
   ## Converts float to its string representation and appends it to `result`.

lib/system.nim

@@ -1871,14 +1871,14 @@ when defined(js) or defined(nimdoc):
       tmp.add(cstring("ab"))
       tmp.add(cstring("cd"))
       doAssert tmp == "abcd"
-    asm """
+    {.emit: """
       if (`x` === null) { `x` = []; }
       var off = `x`.length;
       `x`.length += `y`.length;
       for (var i = 0; i < `y`.length; ++i) {
         `x`[off+i] = `y`.charCodeAt(i);
       }
-    """
+    """.}
   proc add*(x: var cstring, y: cstring) {.magic: "AppendStrStr".} =
     ## Appends `y` to `x` in place.
     ## Only implemented for JS backend.

lib/system/comparisons.nim

@@ -324,7 +324,7 @@ proc `==`*[T](x, y: seq[T]): bool {.noSideEffect.} =
         return true
     else:
       var sameObject = false
-      asm """`sameObject` = `x` === `y`"""
+      {.emit: """`sameObject` = `x` === `y`""".}
       if sameObject: return true
 
   if x.len != y.len: