adds an option to interleave the generated code with snippets from the original source

Lines from the original source are outputted as comments next to line directives.
Hopefully, this will make debugging codegen problems easier.

Other changes:
The frame setup code now uses a single-line C macro. My motivation was to reduce
the noise in the generated output and make it easier to step over the boiler-plate
code, but counter-intuitively this also improved the overall compilation speed a
little bit so I applied the same treatment to line tracking too (this reduces the size of
the generated files and the explanation is that probably the I/O overhead dominates
the macro expansion costs).

compiler/msgs.nim

@@ -8,7 +8,7 @@
 #
 
 import
-  options, strutils, os, tables, sockets
+  options, strutils, os, tables, sockets, ropes, platform
 
 type 
   TMsgKind* = enum 
@@ -403,6 +403,14 @@ type
   TFileInfo*{.final.} = object 
     fullPath*: string          # This is a canonical full filesystem path
     projPath*: string          # This is relative to the project's root
+    
+    quotedName*: PRope         # cached quoted short name for codegen
+                               # purpoes
+    
+    lines*: seq[PRope]         # the source code of the module
+                               #   used for better error messages and
+                               #   embedding the original source in the
+                               #   generated code
 
   TLineInfo*{.final.} = object # This is designed to be as small as possible,
                                # because it is used
@@ -424,11 +432,40 @@ var
   fileInfos*: seq[TFileInfo] = @[]
   SystemFileIdx*: int32
 
+proc toCChar*(c: Char): string = 
+  case c
+  of '\0'..'\x1F', '\x80'..'\xFF': result = '\\' & toOctal(c)
+  of '\'', '\"', '\\': result = '\\' & c
+  else: result = $(c)
+
+proc makeCString*(s: string): PRope =
+  # BUGFIX: We have to split long strings into many ropes. Otherwise
+  # this could trigger an InternalError(). See the ropes module for
+  # further information.
+  const 
+    MaxLineLength = 64
+  result = nil
+  var res = "\""
+  for i in countup(0, len(s) - 1):
+    if (i + 1) mod MaxLineLength == 0:
+      add(res, '\"')
+      add(res, tnl)
+      app(result, toRope(res)) # reset:
+      setlen(res, 1)
+      res[0] = '\"'
+    add(res, toCChar(s[i]))
+  add(res, '\"')
+  app(result, toRope(res))
+
+
 proc newFileInfo(fullPath, projPath: string): TFileInfo =
   result.fullPath = fullPath
   #shallow(result.fullPath)
   result.projPath = projPath
   #shallow(result.projPath)
+  result.quotedName = projPath.extractFilename.makeCString
+  if optEmbedOrigSrc in gGlobalOptions or true:
+    result.lines = @[]
 
 proc fileInfoIdx*(filename: string): int32 =
   var
@@ -524,11 +561,11 @@ proc getInfoContext*(index: int): TLineInfo =
   if i >=% L: result = UnknownLineInfo()
   else: result = msgContext[i]
 
-proc ToFilename*(info: TLineInfo): string =
+proc toFilename*(info: TLineInfo): string =
   if info.fileIndex < 0: result = "???"
   else: result = fileInfos[info.fileIndex].projPath
 
-proc ToFilename*(fileIdx: int32): string =
+proc toFilename*(fileIdx: int32): string =
   if fileIdx < 0: result = "???"
   else: result = fileInfos[fileIdx].projPath
 
@@ -536,7 +573,7 @@ proc toFullPath*(info: TLineInfo): string =
   if info.fileIndex < 0: result = "???"
   else: result = fileInfos[info.fileIndex].fullPath
   
-proc ToLinenumber*(info: TLineInfo): int {.inline.} = 
+proc toLinenumber*(info: TLineInfo): int {.inline.} = 
   result = info.line
 
 proc toColumn*(info: TLineInfo): int {.inline.} = 
@@ -714,3 +751,28 @@ template AssertNotNil*(e: expr): expr =
 
 template InternalAssert*(e: bool): stmt =
   if not e: InternalError($InstantiationInfo())
+
+proc addSourceLine*(fileIdx: int32, line: string) =
+  fileInfos[fileIdx].lines.add line.toRope
+
+proc sourceLine*(i: TLineInfo): PRope =
+  if i.fileIndex < 0: return nil
+  InternalAssert i.fileIndex < fileInfos.len and
+                 i.line <= fileInfos[i.fileIndex].lines.len
+
+  result = fileInfos[i.fileIndex].lines[i.line-1]
+
+proc quotedFilename*(i: TLineInfo): PRope =
+  InternalAssert i.fileIndex >= 0
+  result = fileInfos[i.fileIndex].quotedName
+
+ropes.ErrorHandler = proc (err: TRopesError, msg: string, useWarning: bool) =
+  case err
+  of rInvalidFormatStr:
+    internalError("ropes: invalid format string: " & msg)
+  of rTokenTooLong:
+    internalError("ropes: token too long: " & msg)
+  of rCannotOpenFile:
+    rawMessage(if useWarning: warnCannotOpenFile else: errCannotOpenFile,
+               msg)
+