use cbuilder for tuple/object generation (#24145)

based on #24127

Needs some tweaks to replace the other `struct` type generations, e.g.
seqs, maybe by exposing `BaseTypeKind` as a parameter. C++ and
codegenDecl etc seem like they are going to need attention.

Also `Builder` should really be `distinct string` that one has to call
`extract` on, but for this to be optimal in the current codegen, we
would need something like:

```nim
template buildInto(s: var string, builderName: untyped, body) =
  template `builderName`: untyped = Builder(s)
  body

buildInto(result, builder):
  builder.add ...
```

but this could be a separate PR since it might not work with the
compiler. The possibly-not-optimal alternative is to do:

```nim
template build(builderName: untyped, body): string =
  var `builderName` = Builder("")
  body
  extract(`builderName`)

result = build(builder):
  builder.add ...
```

where the compiler maybe copies the built string but shouldn't.

---------

Co-authored-by: ringabout <43030857+ringabout@users.noreply.github.com>

3 files changed, 153 insertions, 103 deletions

diff --git a/compiler/cbuilder.nim b/compiler/cbuilder.nim
new file mode 100644
index 000000000..6fc0bd881
--- /dev/null
+++ b/compiler/cbuilder.nim
@@ -0,0 +1,121 @@
+type
+  Snippet = string
+  Builder = string
+
+template newBuilder(s: string): Builder =
+  s
+
+proc addField(obj: var Builder; name, typ: Snippet) =
+  obj.add('\t')
+  obj.add(typ)
+  obj.add(" ")
+  obj.add(name)
+  obj.add(";\n")
+
+proc addField(obj: var Builder; field: PSym; name, typ: Snippet; isFlexArray: bool; initializer: Snippet) =
+  obj.add('\t')
+  if field.alignment > 0:
+    obj.add("NIM_ALIGN(")
+    obj.addInt(field.alignment)
+    obj.add(") ")
+  obj.add(typ)
+  if sfNoalias in field.flags:
+    obj.add(" NIM_NOALIAS")
+  obj.add(" ")
+  obj.add(name)
+  if isFlexArray:
+    obj.add("[SEQ_DECL_SIZE]")
+  if field.bitsize != 0:
+    obj.add(":")
+    obj.addInt(field.bitsize)
+  if initializer.len != 0:
+    obj.add(initializer)
+  obj.add(";\n")
+
+proc structOrUnion(t: PType): Snippet =
+  let t = t.skipTypes({tyAlias, tySink})
+  if tfUnion in t.flags: "union"
+  else: "struct"
+
+proc ptrType(t: Snippet): Snippet =
+  t & "*"
+
+template addStruct(obj: var Builder; m: BModule; typ: PType; name: string; baseType: string; body: typed) =
+  if tfPacked in typ.flags:
+    if hasAttribute in CC[m.config.cCompiler].props:
+      obj.add(structOrUnion(typ))
+      obj.add(" __attribute__((__packed__))")
+    else:
+      obj.add("#pragma pack(push, 1)\n")
+      obj.add(structOrUnion(typ))
+  else:
+    obj.add(structOrUnion(typ))
+  obj.add(" ")
+  obj.add(name)
+  type BaseClassKind = enum
+    bcNone, bcCppInherit, bcSupField, bcNoneRtti, bcNoneTinyRtti
+  var baseKind = bcNone
+  if typ.kind == tyObject:
+    if typ.baseClass == nil:
+      if lacksMTypeField(typ):
+        baseKind = bcNone
+      elif optTinyRtti in m.config.globalOptions:
+        baseKind = bcNoneTinyRtti
+      else:
+        baseKind = bcNoneRtti
+    elif m.compileToCpp:
+      baseKind = bcCppInherit
+    else:
+      baseKind = bcSupField
+  if baseKind == bcCppInherit:
+    obj.add(" : public ")
+    obj.add(baseType)
+  obj.add(" ")
+  obj.add("{\n")
+  let currLen = obj.len
+  case baseKind
+  of bcNone:
+    # rest of the options add a field or don't need it due to inheritance,
+    # we need to add the dummy field for uncheckedarray ahead of time
+    # so that it remains trailing
+    if typ.itemId notin m.g.graph.memberProcsPerType and
+        typ.n != nil and typ.n.len == 1 and typ.n[0].kind == nkSym and
+        typ.n[0].sym.typ.skipTypes(abstractInst).kind == tyUncheckedArray:
+      # only consists of flexible array field, add *initial* dummy field
+      obj.addField(name = "dummy", typ = "char")
+  of bcCppInherit: discard
+  of bcNoneRtti:
+    obj.addField(name = "m_type", typ = ptrType(cgsymValue(m, "TNimType")))
+  of bcNoneTinyRtti:
+    obj.addField(name = "m_type", typ = ptrType(cgsymValue(m, "TNimTypeV2")))
+  of bcSupField:
+    obj.addField(name = "Sup", typ = baseType)
+  body
+  if baseKind == bcNone and currLen == obj.len and typ.itemId notin m.g.graph.memberProcsPerType:
+    # no fields were added, add dummy field
+    obj.addField(name = "dummy", typ = "char")
+  obj.add("};\n")
+  if tfPacked in typ.flags and hasAttribute notin CC[m.config.cCompiler].props:
+    result.add("#pragma pack(pop)\n")
+
+template addFieldWithStructType(obj: var Builder; m: BModule; parentTyp: PType; fieldName: string, body: typed) =
+  ## adds a field with a `struct { ... }` type, building it according to `body`
+  obj.add('\t')
+  if tfPacked in parentTyp.flags:
+    if hasAttribute in CC[m.config.cCompiler].props:
+      obj.add("struct __attribute__((__packed__)) {\n")
+    else:
+      obj.add("#pragma pack(push, 1)\nstruct {")
+  else:
+    obj.add("struct {\n")
+  body
+  obj.add("} ")
+  obj.add(fieldName)
+  obj.add(";\n")
+  if tfPacked in parentTyp.flags and hasAttribute notin CC[m.config.cCompiler].props:
+    result.add("#pragma pack(pop)\n")
+
+template addAnonUnion(obj: var Builder; body: typed) =
+  obj.add "union{\n"
+  body
+  obj.add("};\n")
diff --git a/compiler/ccgtypes.nim b/compiler/ccgtypes.nim
index 5c3e82346..5b5218a3e 100644
--- a/compiler/ccgtypes.nim
+++ b/compiler/ccgtypes.nim
@@ -376,11 +376,6 @@ proc getTypePre(m: BModule; typ: PType; sig: SigHash): Rope =
     result = getSimpleTypeDesc(m, typ)
     if result == "": result = cacheGetType(m.typeCache, sig)
 
-proc structOrUnion(t: PType): Rope =
-  let t = t.skipTypes({tyAlias, tySink})
-  if tfUnion in t.flags: "union"
-  else: "struct"
-
 proc addForwardStructFormat(m: BModule; structOrUnion: Rope, typename: Rope) =
   if m.compileToCpp:
     m.s[cfsForwardTypes].addf "$1 $2;$n", [structOrUnion, typename]
@@ -698,7 +693,7 @@ proc genCppInitializer(m: BModule, prc: BProc; typ: PType; didGenTemp: var bool)
 
 proc genRecordFieldsAux(m: BModule; n: PNode,
                         rectype: PType,
-                        check: var IntSet; result: var Rope; unionPrefix = "") =
+                        check: var IntSet; result: var Builder; unionPrefix = "") =
   case n.kind
   of nkRecList:
     for i in 0..<n.len:
@@ -715,64 +710,51 @@ proc genRecordFieldsAux(m: BModule; n: PNode,
         let k = lastSon(n[i])
         if k.kind != nkSym:
           let structName = "_" & mangleRecFieldName(m, n[0].sym) & "_" & $i
-          var a = newRopeAppender()
+          var a = newBuilder("")
           genRecordFieldsAux(m, k, rectype, check, a, unionPrefix & $structName & ".")
-          if a != "":
-            if tfPacked notin rectype.flags:
-              unionBody.add("struct {")
-            else:
-              if hasAttribute in CC[m.config.cCompiler].props:
-                unionBody.add("struct __attribute__((__packed__)){")
-              else:
-                unionBody.addf("#pragma pack(push, 1)$nstruct{", [])
-            unionBody.add(a)
-            unionBody.addf("} $1;$n", [structName])
-            if tfPacked in rectype.flags and hasAttribute notin CC[m.config.cCompiler].props:
-              unionBody.addf("#pragma pack(pop)$n", [])
+          if a.len != 0:
+            unionBody.addFieldWithStructType(m, rectype, structName):
+              unionBody.add(a)
         else:
           genRecordFieldsAux(m, k, rectype, check, unionBody, unionPrefix)
       else: internalError(m.config, "genRecordFieldsAux(record case branch)")
-    if unionBody != "":
-      result.addf("union{\n$1};$n", [unionBody])
+    if unionBody.len != 0:
+      result.addAnonUnion:
+        result.add(unionBody)
   of nkSym:
     let field = n.sym
     if field.typ.kind == tyVoid: return
     #assert(field.ast == nil)
     let sname = mangleRecFieldName(m, field)
     fillLoc(field.loc, locField, n, unionPrefix & sname, OnUnknown)
-    if field.alignment > 0:
-      result.addf "NIM_ALIGN($1) ", [rope(field.alignment)]
     # for importcpp'ed objects, we only need to set field.loc, but don't
     # have to recurse via 'getTypeDescAux'. And not doing so prevents problems
     # with heavily templatized C++ code:
     if not isImportedCppType(rectype):
-      let noAlias = if sfNoalias in field.flags: " NIM_NOALIAS" else: ""
-
       let fieldType = field.loc.lode.typ.skipTypes(abstractInst)
+      var typ: Rope = ""
+      var isFlexArray = false
+      var initializer = ""
       if fieldType.kind == tyUncheckedArray:
-        result.addf("\t$1 $2[SEQ_DECL_SIZE];$n",
-            [getTypeDescAux(m, fieldType.elemType, check, dkField), sname])
+        typ = getTypeDescAux(m, fieldType.elemType, check, dkField)
+        isFlexArray = true
       elif fieldType.kind == tySequence:
         # we need to use a weak dependency here for trecursive_table.
-        result.addf("\t$1$3 $2;$n", [getTypeDescWeak(m, field.loc.t, check, dkField), sname, noAlias])
-      elif field.bitsize != 0:
-        result.addf("\t$1$4 $2:$3;$n", [getTypeDescAux(m, field.loc.t, check, dkField), sname, rope($field.bitsize), noAlias])
+        typ = getTypeDescWeak(m, field.loc.t, check, dkField)
       else:
+        typ = getTypeDescAux(m, field.loc.t, check, dkField)
         # don't use fieldType here because we need the
         # tyGenericInst for C++ template support
         let noInit = sfNoInit in field.flags or (field.typ.sym != nil and sfNoInit in field.typ.sym.flags)
         if not noInit and (fieldType.isOrHasImportedCppType() or hasCppCtor(m, field.owner.typ)):
           var didGenTemp = false
-          var initializer = genCppInitializer(m, nil, fieldType, didGenTemp)
-          result.addf("\t$1$3 $2$4;$n", [getTypeDescAux(m, field.loc.t, check, dkField), sname, noAlias, initializer])
-        else:
-          result.addf("\t$1$3 $2;$n", [getTypeDescAux(m, field.loc.t, check, dkField), sname, noAlias])
+          initializer = genCppInitializer(m, nil, fieldType, didGenTemp)
+      result.addField(field, sname, typ, isFlexArray, initializer)
   else: internalError(m.config, n.info, "genRecordFieldsAux()")
 
 proc genMemberProcHeader(m: BModule; prc: PSym; result: var Rope; asPtr: bool = false, isFwdDecl:bool = false)
 
-proc getRecordFields(m: BModule; typ: PType, check: var IntSet): Rope =
-  result = newRopeAppender()
+proc addRecordFields(result: var Builder; m: BModule; typ: PType, check: var IntSet) =
   genRecordFieldsAux(m, typ.n, typ, check, result)
   if typ.itemId in m.g.graph.memberProcsPerType:
     let procs = m.g.graph.memberProcsPerType[typ.itemId]
@@ -794,88 +776,34 @@ proc fillObjectFields*(m: BModule; typ: PType) =
   # sometimes generic objects are not consistently merged. We patch over
   # this fact here.
   var check = initIntSet()
-  discard getRecordFields(m, typ, check)
+  var ignored = newBuilder("")
+  addRecordFields(ignored, m, typ, check)
 
 proc mangleDynLibProc(sym: PSym): Rope
 
-proc getRecordDescAux(m: BModule; typ: PType, name, baseType: Rope,
-                   check: var IntSet, hasField:var bool): Rope =
-  result = ""
-  if typ.kind == tyObject:
-    if typ.baseClass == nil:
-      if lacksMTypeField(typ):
-        appcg(m, result, " {$n", [])
-      else:
-        if optTinyRtti in m.config.globalOptions:
-          appcg(m, result, " {$n#TNimTypeV2* m_type;$n", [])
-        else:
-          appcg(m, result, " {$n#TNimType* m_type;$n", [])
-        hasField = true
-    elif m.compileToCpp:
-      appcg(m, result, " : public $1 {$n", [baseType])
-      if typ.isException and m.config.exc == excCpp:
-        when false:
-          appcg(m, result, "virtual void raise() { throw *this; }$n", []) # required for polymorphic exceptions
-          if typ.sym.magic == mException:
-            # Add cleanup destructor to Exception base class
-            appcg(m, result, "~$1();$n", [name])
-            # define it out of the class body and into the procs section so we don't have to
-            # artificially forward-declare popCurrentExceptionEx (very VERY troublesome for HCR)
-            appcg(m, cfsProcs, "inline $1::~$1() {if(this->raiseId) #popCurrentExceptionEx(this->raiseId);}$n", [name])
-      hasField = true
-    else:
-      appcg(m, result, " {$n  $1 Sup;$n", [baseType])
-      hasField = true
-  else:
-    result.addf(" {$n", [name])
-
 proc getRecordDesc(m: BModule; typ: PType, name: Rope,
                    check: var IntSet): Rope =
   # declare the record:
-  var hasField = false
-  var structOrUnion: string
-  if tfPacked in typ.flags:
-      if hasAttribute in CC[m.config.cCompiler].props:
-        structOrUnion = structOrUnion(typ) & " __attribute__((__packed__))"
-      else:
-        structOrUnion = "#pragma pack(push, 1)\L" & structOrUnion(typ)
-  else:
-    structOrUnion = structOrUnion(typ)
   var baseType: string = ""
   if typ.baseClass != nil:
     baseType = getTypeDescAux(m, typ.baseClass.skipTypes(skipPtrs), check, dkField)
   if typ.sym == nil or sfCodegenDecl notin typ.sym.flags:
-    result = structOrUnion & " " & name
-    result.add(getRecordDescAux(m, typ, name, baseType, check, hasField))
-    let desc = getRecordFields(m, typ, check)
-    if not hasField and typ.itemId notin m.g.graph.memberProcsPerType:
-      if desc == "":
-        result.add("\tchar dummy;\n")
-      elif typ.n.len == 1 and typ.n[0].kind == nkSym:
-        let field = typ.n[0].sym
-        let fieldType = field.typ.skipTypes(abstractInst)
-        if fieldType.kind == tyUncheckedArray:
-          result.add("\tchar dummy;\n")
-      result.add(desc)
-    else:
-      result.add(desc)
-    result.add("};\L")
+    result = newBuilder("")
+    result.addStruct(m, typ, name, baseType):
+      result.addRecordFields(m, typ, check)
   else:
-    let desc = getRecordFields(m, typ, check)
+    var desc = newBuilder("")
+    desc.addRecordFields(m, typ, check)
     result = runtimeFormat(typ.sym.cgDeclFrmt, [name, desc, baseType])
-  if tfPacked in typ.flags and hasAttribute notin CC[m.config.cCompiler].props:
-    result.add "#pragma pack(pop)\L"
 
 proc getTupleDesc(m: BModule; typ: PType, name: Rope,
                   check: var IntSet): Rope =
-  result = "$1 $2 {$n" % [structOrUnion(typ), name]
-  var desc: Rope = ""
-  for i, a in typ.ikids:
-    desc.addf("$1 Field$2;$n",
-         [getTypeDescAux(m, a, check, dkField), rope(i)])
-  if desc == "": result.add("char dummy;\L")
-  else: result.add(desc)
-  result.add("};\L")
+  result = newBuilder("")
+  result.addStruct(m, typ, name, ""):
+    for i, a in typ.ikids:
+      result.addField(
+        name = "Field" & $i,
+        typ = getTypeDescAux(m, a, check, dkField))
 
 proc scanCppGenericSlot(pat: string, cursor, outIdx, outStars: var int): bool =
   # A helper proc for handling cppimport patterns, involving numeric
diff --git a/compiler/cgen.nim b/compiler/cgen.nim
index 8a6bd96ec..091f5c842 100644
--- a/compiler/cgen.nim
+++ b/compiler/cgen.nim
@@ -373,6 +373,7 @@ proc dataField(p: BProc): Rope =
 
 proc genProcPrototype(m: BModule, sym: PSym)
 
+include cbuilder
 include ccgliterals
 include ccgtypes