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-rw-r--r--compiler/lookups.nim865
1 files changed, 662 insertions, 203 deletions
diff --git a/compiler/lookups.nim b/compiler/lookups.nim
index 87694988a..d8fcf73e0 100644
--- a/compiler/lookups.nim
+++ b/compiler/lookups.nim
@@ -8,10 +8,16 @@
 #
 
 # This module implements lookup helpers.
+import std/[algorithm, strutils, tables]
+
+when defined(nimPreviewSlimSystem):
+  import std/assertions
 
 import
-  intsets, ast, astalgo, idents, semdata, types, msgs, options,
-  renderer, wordrecg, idgen, nimfix.prettybase, lineinfos, strutils
+  ast, astalgo, idents, semdata, types, msgs, options,
+  renderer, lineinfos, modulegraphs, astmsgs, wordrecg
+
+import std/[intsets, sets]
 
 proc ensureNoMissingOrUnusedSymbols(c: PContext; scope: PScope)
 
@@ -36,34 +42,41 @@ proc considerQuotedIdent*(c: PContext; n: PNode, origin: PNode = nil): PIdent =
   of nkAccQuoted:
     case n.len
     of 0: handleError(n, origin)
-    of 1: result = considerQuotedIdent(c, n.sons[0], origin)
+    of 1: result = considerQuotedIdent(c, n[0], origin)
     else:
       var id = ""
       for i in 0..<n.len:
-        let x = n.sons[i]
+        let x = n[i]
         case x.kind
         of nkIdent: id.add(x.ident.s)
         of nkSym: id.add(x.sym.name.s)
+        of nkSymChoices, nkOpenSym:
+          if x[0].kind == nkSym:
+            id.add(x[0].sym.name.s)
+          else:
+            handleError(n, origin)
         of nkLiterals - nkFloatLiterals: id.add(x.renderTree)
         else: handleError(n, origin)
       result = getIdent(c.cache, id)
   of nkOpenSymChoice, nkClosedSymChoice:
     if n[0].kind == nkSym:
-      result = n.sons[0].sym.name
+      result = n[0].sym.name
     else:
       handleError(n, origin)
+  of nkOpenSym:
+    result = considerQuotedIdent(c, n[0], origin)
   else:
     handleError(n, origin)
 
 template addSym*(scope: PScope, s: PSym) =
   strTableAdd(scope.symbols, s)
 
-proc addUniqueSym*(scope: PScope, s: PSym): bool =
-  result = not strTableIncl(scope.symbols, s)
+proc addUniqueSym*(scope: PScope, s: PSym): PSym =
+  result = strTableInclReportConflict(scope.symbols, s)
 
 proc openScope*(c: PContext): PScope {.discardable.} =
   result = PScope(parent: c.currentScope,
-                  symbols: newStrTable(),
+                  symbols: initStrTable(),
                   depthLevel: c.scopeDepth + 1)
   c.currentScope = result
 
@@ -74,67 +87,242 @@ proc closeScope*(c: PContext) =
   ensureNoMissingOrUnusedSymbols(c, c.currentScope)
   rawCloseScope(c)
 
-iterator walkScopes*(scope: PScope): PScope =
+iterator allScopes*(scope: PScope): PScope =
   var current = scope
   while current != nil:
     yield current
     current = current.parent
 
-proc skipAlias*(s: PSym; n: PNode; conf: ConfigRef): PSym =
-  if s == nil or s.kind != skAlias:
-    result = s
-  else:
-    result = s.owner
-    if conf.cmd == cmdPretty:
-      prettybase.replaceDeprecated(conf, n.info, s, result)
-    else:
-      message(conf, n.info, warnDeprecated, "use " & result.name.s & " instead; " &
-              s.name.s)
+iterator localScopesFrom*(c: PContext; scope: PScope): PScope =
+  for s in allScopes(scope):
+    if s == c.topLevelScope: break
+    yield s
 
-proc localSearchInScope*(c: PContext, s: PIdent): PSym =
-  result = strTableGet(c.currentScope.symbols, s)
+proc isShadowScope*(s: PScope): bool {.inline.} =
+  s.parent != nil and s.parent.depthLevel == s.depthLevel
 
-proc searchInScopes*(c: PContext, s: PIdent): PSym =
-  for scope in walkScopes(c.currentScope):
+proc localSearchInScope*(c: PContext, s: PIdent): PSym =
+  var scope = c.currentScope
+  result = strTableGet(scope.symbols, s)
+  while result == nil and scope.isShadowScope:
+    # We are in a shadow scope, check in the parent too
+    scope = scope.parent
     result = strTableGet(scope.symbols, s)
-    if result != nil: return
+
+proc initIdentIter(ti: var ModuleIter; marked: var IntSet; im: ImportedModule; name: PIdent;
+                   g: ModuleGraph): PSym =
+  result = initModuleIter(ti, g, im.m, name)
+  while result != nil:
+    let b =
+      case im.mode
+      of importAll: true
+      of importSet: result.id in im.imported
+      of importExcept: name.id notin im.exceptSet
+    if b and not containsOrIncl(marked, result.id):
+      return result
+    result = nextModuleIter(ti, g)
+
+proc nextIdentIter(ti: var ModuleIter; marked: var IntSet; im: ImportedModule;
+                   g: ModuleGraph): PSym =
+  while true:
+    result = nextModuleIter(ti, g)
+    if result == nil: return nil
+    case im.mode
+    of importAll:
+      if not containsOrIncl(marked, result.id):
+        return result
+    of importSet:
+      if result.id in im.imported and not containsOrIncl(marked, result.id):
+        return result
+    of importExcept:
+      if result.name.id notin im.exceptSet and not containsOrIncl(marked, result.id):
+        return result
+
+iterator symbols(im: ImportedModule; marked: var IntSet; name: PIdent; g: ModuleGraph): PSym =
+  var ti: ModuleIter = default(ModuleIter)
+  var candidate = initIdentIter(ti, marked, im, name, g)
+  while candidate != nil:
+    yield candidate
+    candidate = nextIdentIter(ti, marked, im, g)
+
+iterator importedItems*(c: PContext; name: PIdent): PSym =
+  var marked = initIntSet()
+  for im in c.imports.mitems:
+    for s in symbols(im, marked, name, c.graph):
+      yield s
+
+proc allPureEnumFields(c: PContext; name: PIdent): seq[PSym] =
+  var ti: TIdentIter = default(TIdentIter)
+  result = @[]
+  var res = initIdentIter(ti, c.pureEnumFields, name)
+  while res != nil:
+    result.add res
+    res = nextIdentIter(ti, c.pureEnumFields)
+
+iterator allSyms*(c: PContext): (PSym, int, bool) =
+  # really iterate over all symbols in all the scopes. This is expensive
+  # and only used by suggest.nim.
+  var isLocal = true
+
+  var scopeN = 0
+  for scope in allScopes(c.currentScope):
+    if scope == c.topLevelScope: isLocal = false
+    dec scopeN
+    for item in scope.symbols:
+      yield (item, scopeN, isLocal)
+
+  dec scopeN
+  isLocal = false
+  for im in c.imports.mitems:
+    for s in modulegraphs.allSyms(c.graph, im.m):
+      assert s != nil
+      yield (s, scopeN, isLocal)
+
+iterator uniqueSyms*(c: PContext): (PSym, int, bool) =
+  ## Like [allSyms] except only returns unique symbols (Uniqueness determined by line + name)
+  # Track seen symbols so we don't duplicate them.
+  # The int is for the symbols name, and line info is
+  # to be able to tell apart symbols with same name but on different lines
+  var seen = initHashSet[(TLineInfo, int)]()
+  for res in allSyms(c):
+    if not seen.containsOrIncl((res[0].info, res[0].name.id)):
+      yield res
+
+
+proc someSymFromImportTable*(c: PContext; name: PIdent; ambiguous: var bool): PSym =
+  var marked = initIntSet()
+  var symSet = OverloadableSyms
   result = nil
+  block outer:
+    for im in c.imports.mitems:
+      for s in symbols(im, marked, name, c.graph):
+        if result == nil:
+          result = s
+        elif s.kind notin symSet or result.kind notin symSet:
+          ambiguous = true
+          break outer
+
+proc searchInScopes*(c: PContext, s: PIdent; ambiguous: var bool): PSym =
+  for scope in allScopes(c.currentScope):
+    result = strTableGet(scope.symbols, s)
+    if result != nil: return result
+  result = someSymFromImportTable(c, s, ambiguous)
 
-when declared(echo):
-  proc debugScopes*(c: PContext; limit=0) {.deprecated.} =
-    var i = 0
-    for scope in walkScopes(c.currentScope):
-      echo "scope ", i
-      for h in 0 .. high(scope.symbols.data):
-        if scope.symbols.data[h] != nil:
-          echo scope.symbols.data[h].name.s
-      if i == limit: break
-      inc i
-
-proc searchInScopes*(c: PContext, s: PIdent, filter: TSymKinds): PSym =
-  for scope in walkScopes(c.currentScope):
-    var ti: TIdentIter
+proc debugScopes*(c: PContext; limit=0, max = int.high) {.deprecated.} =
+  var i = 0
+  var count = 0
+  for scope in allScopes(c.currentScope):
+    echo "scope ", i
+    for h in 0..high(scope.symbols.data):
+      if scope.symbols.data[h] != nil:
+        if count >= max: return
+        echo count, ": ", scope.symbols.data[h].name.s
+        count.inc
+    if i == limit: return
+    inc i
+
+proc searchInScopesAllCandidatesFilterBy*(c: PContext, s: PIdent, filter: TSymKinds): seq[PSym] =
+  result = @[]
+  for scope in allScopes(c.currentScope):
+    var ti: TIdentIter = default(TIdentIter)
     var candidate = initIdentIter(ti, scope.symbols, s)
     while candidate != nil:
-      if candidate.kind in filter: return candidate
+      if candidate.kind in filter:
+        result.add candidate
       candidate = nextIdentIter(ti, scope.symbols)
-  result = nil
 
-proc errorSym*(c: PContext, n: PNode): PSym =
+  if result.len == 0:
+    var marked = initIntSet()
+    for im in c.imports.mitems:
+      for s in symbols(im, marked, s, c.graph):
+        if s.kind in filter:
+          result.add s
+
+proc searchInScopesFilterBy*(c: PContext, s: PIdent, filter: TSymKinds): seq[PSym] =
+  result = @[]
+  block outer:
+    for scope in allScopes(c.currentScope):
+      var ti: TIdentIter = default(TIdentIter)
+      var candidate = initIdentIter(ti, scope.symbols, s)
+      while candidate != nil:
+        if candidate.kind in filter:
+          result.add candidate
+          # Break here, because further symbols encountered would be shadowed
+          break outer
+        candidate = nextIdentIter(ti, scope.symbols)
+
+  if result.len == 0:
+    var marked = initIntSet()
+    for im in c.imports.mitems:
+      for s in symbols(im, marked, s, c.graph):
+        if s.kind in filter:
+          result.add s
+
+proc cmpScopes*(ctx: PContext, s: PSym): int =
+  # Do not return a negative number
+  if s.originatingModule == ctx.module:
+    result = 2
+    var owner = s
+    while true:
+      owner = owner.skipGenericOwner
+      if owner.kind == skModule: break
+      inc result
+  else:
+    result = 1
+
+proc isAmbiguous*(c: PContext, s: PIdent, filter: TSymKinds, sym: var PSym): bool =
+  result = false
+  block outer:
+    for scope in allScopes(c.currentScope):
+      var ti: TIdentIter = default(TIdentIter)
+      var candidate = initIdentIter(ti, scope.symbols, s)
+      var scopeHasCandidate = false
+      while candidate != nil:
+        if candidate.kind in filter:
+          if scopeHasCandidate:
+            # 2 candidates in same scope, ambiguous
+            return true
+          else:
+            scopeHasCandidate = true
+            sym = candidate
+        candidate = nextIdentIter(ti, scope.symbols)
+      if scopeHasCandidate:
+        # scope had a candidate but wasn't ambiguous
+        return false
+
+  var importsHaveCandidate = false
+  var marked = initIntSet()
+  for im in c.imports.mitems:
+    for s in symbols(im, marked, s, c.graph):
+      if s.kind in filter:
+        if importsHaveCandidate:
+          # 2 candidates among imports, ambiguous
+          return true
+        else:
+          importsHaveCandidate = true
+          sym = s
+  if importsHaveCandidate:
+    # imports had a candidate but wasn't ambiguous
+    return false
+
+proc errorSym*(c: PContext, ident: PIdent, info: TLineInfo): PSym =
   ## creates an error symbol to avoid cascading errors (for IDE support)
+  result = newSym(skError, ident, c.idgen, getCurrOwner(c), info, {})
+  result.typ = errorType(c)
+  incl(result.flags, sfDiscardable)
+  # pretend it's from the top level scope to prevent cascading errors:
+  if c.config.cmd != cmdInteractive and c.compilesContextId == 0:
+    c.moduleScope.addSym(result)
+
+proc errorSym*(c: PContext, n: PNode): PSym =
   var m = n
   # ensure that 'considerQuotedIdent' can't fail:
-  if m.kind == nkDotExpr: m = m.sons[1]
+  if m.kind == nkDotExpr: m = m[1]
   let ident = if m.kind in {nkIdent, nkSym, nkAccQuoted}:
       considerQuotedIdent(c, m)
     else:
       getIdent(c.cache, "err:" & renderTree(m))
-  result = newSym(skError, ident, getCurrOwner(c), n.info, {})
-  result.typ = errorType(c)
-  incl(result.flags, sfDiscardable)
-  # pretend it's imported from some unknown module to prevent cascading errors:
-  if c.config.cmd != cmdInteractive and c.compilesContextId == 0:
-    c.importTable.addSym(result)
+  result = errorSym(c, ident, n.info)
 
 type
   TOverloadIterMode* = enum
@@ -142,152 +330,309 @@ type
     oimSymChoiceLocalLookup
   TOverloadIter* = object
     it*: TIdentIter
+    mit*: ModuleIter
     m*: PSym
     mode*: TOverloadIterMode
     symChoiceIndex*: int
-    scope*: PScope
-    inSymChoice: IntSet
+    currentScope: PScope
+    importIdx: int
+    marked: IntSet
 
-proc getSymRepr*(conf: ConfigRef; s: PSym): string =
+proc getSymRepr*(conf: ConfigRef; s: PSym, getDeclarationPath = true): string =
   case s.kind
-  of skProc, skFunc, skMethod, skConverter, skIterator:
-    result = getProcHeader(conf, s)
+  of routineKinds, skType:
+    result = getProcHeader(conf, s, getDeclarationPath = getDeclarationPath)
   else:
-    result = s.name.s
+    result = "'$1'" % s.name.s
+    if getDeclarationPath:
+      result.addDeclaredLoc(conf, s)
 
 proc ensureNoMissingOrUnusedSymbols(c: PContext; scope: PScope) =
   # check if all symbols have been used and defined:
-  var it: TTabIter
+  var it: TTabIter = default(TTabIter)
   var s = initTabIter(it, scope.symbols)
   var missingImpls = 0
+  var unusedSyms: seq[tuple[sym: PSym, key: string]] = @[]
   while s != nil:
-    if sfForward in s.flags and s.kind != skType:
+    if sfForward in s.flags and s.kind notin {skType, skModule}:
       # too many 'implementation of X' errors are annoying
       # and slow 'suggest' down:
       if missingImpls == 0:
         localError(c.config, s.info, "implementation of '$1' expected" %
-            getSymRepr(c.config, s))
+            getSymRepr(c.config, s, getDeclarationPath=false))
       inc missingImpls
-    elif {sfUsed, sfExported} * s.flags == {} and optHints in s.options:
-      if s.kind notin {skForVar, skParam, skMethod, skUnknown, skGenericParam}:
+    elif {sfUsed, sfExported} * s.flags == {}:
+      if s.kind notin {skForVar, skParam, skMethod, skUnknown, skGenericParam, skEnumField}:
         # XXX: implicit type params are currently skTypes
         # maybe they can be made skGenericParam as well.
         if s.typ != nil and tfImplicitTypeParam notin s.typ.flags and
            s.typ.kind != tyGenericParam:
-          message(c.config, s.info, hintXDeclaredButNotUsed, getSymRepr(c.config, s))
+          unusedSyms.add (s, toFileLineCol(c.config, s.info))
     s = nextIter(it, scope.symbols)
+  for (s, _) in sortedByIt(unusedSyms, it.key):
+    message(c.config, s.info, hintXDeclaredButNotUsed, s.name.s)
 
-proc wrongRedefinition*(c: PContext; info: TLineInfo, s: string) =
+proc wrongRedefinition*(c: PContext; info: TLineInfo, s: string;
+                        conflictsWith: TLineInfo, note = errGenerated) =
+  ## Emit a redefinition error if in non-interactive mode
   if c.config.cmd != cmdInteractive:
-    localError(c.config, info, "redefinition of '$1'" % s)
+    localError(c.config, info, note,
+      "redefinition of '$1'; previous declaration here: $2" %
+      [s, c.config $ conflictsWith])
+
+# xxx pending bootstrap >= 1.4, replace all those overloads with a single one:
+# proc addDecl*(c: PContext, sym: PSym, info = sym.info, scope = c.currentScope) {.inline.} =
+proc addDeclAt*(c: PContext; scope: PScope, sym: PSym, info: TLineInfo) =
+  if sym.name.id == ord(wUnderscore): return
+  let conflict = scope.addUniqueSym(sym)
+  if conflict != nil:
+    if sym.kind == skModule and conflict.kind == skModule:
+      # e.g.: import foo; import foo
+      # xxx we could refine this by issuing a different hint for the case
+      # where a duplicate import happens inside an include.
+      if c.importModuleMap[sym.id] == c.importModuleMap[conflict.id]:
+        #only hints if the conflict is the actual module not just a shared name
+        localError(c.config, info, hintDuplicateModuleImport,
+          "duplicate import of '$1'; previous import here: $2" %
+          [sym.name.s, c.config $ conflict.info])
+    else:
+      wrongRedefinition(c, info, sym.name.s, conflict.info, errGenerated)
 
-proc addDecl*(c: PContext, sym: PSym, info: TLineInfo) =
-  if not c.currentScope.addUniqueSym(sym):
-    wrongRedefinition(c, info, sym.name.s)
+proc addDeclAt*(c: PContext; scope: PScope, sym: PSym) {.inline.} =
+  addDeclAt(c, scope, sym, sym.info)
 
-proc addDecl*(c: PContext, sym: PSym) =
-  if not c.currentScope.addUniqueSym(sym):
-    wrongRedefinition(c, sym.info, sym.name.s)
+proc addDecl*(c: PContext, sym: PSym, info: TLineInfo) {.inline.} =
+  addDeclAt(c, c.currentScope, sym, info)
+
+proc addDecl*(c: PContext, sym: PSym) {.inline.} =
+  addDeclAt(c, c.currentScope, sym)
 
 proc addPrelimDecl*(c: PContext, sym: PSym) =
   discard c.currentScope.addUniqueSym(sym)
 
-proc addDeclAt*(c: PContext; scope: PScope, sym: PSym) =
-  if not scope.addUniqueSym(sym):
-    wrongRedefinition(c, sym.info, sym.name.s)
+from ic / ic import addHidden
 
 proc addInterfaceDeclAux(c: PContext, sym: PSym) =
+  ## adds symbol to the module for either private or public access.
   if sfExported in sym.flags:
     # add to interface:
-    if c.module != nil: strTableAdd(c.module.tab, sym)
+    if c.module != nil: exportSym(c, sym)
     else: internalError(c.config, sym.info, "addInterfaceDeclAux")
+  elif sym.kind in ExportableSymKinds and c.module != nil and isTopLevelInsideDeclaration(c, sym):
+    strTableAdd(semtabAll(c.graph, c.module), sym)
+    if c.config.symbolFiles != disabledSf:
+      addHidden(c.encoder, c.packedRepr, sym)
 
 proc addInterfaceDeclAt*(c: PContext, scope: PScope, sym: PSym) =
+  ## adds a symbol on the scope and the interface if appropriate
   addDeclAt(c, scope, sym)
-  addInterfaceDeclAux(c, sym)
+  if not scope.isShadowScope:
+    # adding into a non-shadow scope, we need to handle exports, etc
+    addInterfaceDeclAux(c, sym)
+
+proc addInterfaceDecl*(c: PContext, sym: PSym) {.inline.} =
+  ## adds a decl and the interface if appropriate
+  addInterfaceDeclAt(c, c.currentScope, sym)
 
 proc addOverloadableSymAt*(c: PContext; scope: PScope, fn: PSym) =
+  ## adds an symbol to the given scope, will check for and raise errors if it's
+  ## a redefinition as opposed to an overload.
   if fn.kind notin OverloadableSyms:
     internalError(c.config, fn.info, "addOverloadableSymAt")
     return
-  let check = strTableGet(scope.symbols, fn.name)
-  if check != nil and check.kind notin OverloadableSyms:
-    wrongRedefinition(c, fn.info, fn.name.s)
-  else:
-    scope.addSym(fn)
-
-proc addInterfaceDecl*(c: PContext, sym: PSym) =
-  # it adds the symbol to the interface if appropriate
-  addDecl(c, sym)
-  addInterfaceDeclAux(c, sym)
+  if fn.name.id != ord(wUnderscore):
+    let check = strTableGet(scope.symbols, fn.name)
+    if check != nil and check.kind notin OverloadableSyms:
+      wrongRedefinition(c, fn.info, fn.name.s, check.info)
+    else:
+      scope.addSym(fn)
 
 proc addInterfaceOverloadableSymAt*(c: PContext, scope: PScope, sym: PSym) =
-  # it adds the symbol to the interface if appropriate
+  ## adds an overloadable symbol on the scope and the interface if appropriate
   addOverloadableSymAt(c, scope, sym)
-  addInterfaceDeclAux(c, sym)
-
-when defined(nimfix):
-  # when we cannot find the identifier, retry with a changed identifer:
-  proc altSpelling(x: PIdent): PIdent =
-    case x.s[0]
-    of 'A'..'Z': result = getIdent(toLowerAscii(x.s[0]) & x.s.substr(1))
-    of 'a'..'z': result = getIdent(toLowerAscii(x.s[0]) & x.s.substr(1))
-    else: result = x
-
-  template fixSpelling(n: PNode; ident: PIdent; op: untyped) =
-    let alt = ident.altSpelling
-    result = op(c, alt).skipAlias(n)
-    if result != nil:
-      prettybase.replaceDeprecated(n.info, ident, alt)
-      return result
-else:
-  template fixSpelling(n: PNode; ident: PIdent; op: untyped) = discard
+  if not scope.isShadowScope:
+    # adding into a non-shadow scope, we need to handle exports, etc
+    addInterfaceDeclAux(c, sym)
+
+proc openShadowScope*(c: PContext) =
+  ## opens a shadow scope, just like any other scope except the depth is the
+  ## same as the parent -- see `isShadowScope`.
+  c.currentScope = PScope(parent: c.currentScope,
+                          symbols: initStrTable(),
+                          depthLevel: c.scopeDepth)
+
+proc closeShadowScope*(c: PContext) =
+  ## closes the shadow scope, but doesn't merge any of the symbols
+  ## Does not check for unused symbols or missing forward decls since a macro
+  ## or template consumes this AST
+  rawCloseScope(c)
+
+proc mergeShadowScope*(c: PContext) =
+  ## close the existing scope and merge in all defined symbols, this will also
+  ## trigger any export related code if this is into a non-shadow scope.
+  ##
+  ## Merges:
+  ## shadow -> shadow: add symbols to the parent but check for redefinitions etc
+  ## shadow -> non-shadow: the above, but also handle exports and all that
+  let shadowScope = c.currentScope
+  c.rawCloseScope
+  for sym in shadowScope.symbols:
+    if sym.kind in OverloadableSyms:
+      c.addInterfaceOverloadableSymAt(c.currentScope, sym)
+    else:
+      c.addInterfaceDecl(sym)
+
+
+import std/[editdistance, heapqueue]
+
+type SpellCandidate = object
+  dist: int
+  depth: int
+  msg: string
+  sym: PSym
+
+template toOrderTup(a: SpellCandidate): (int, int, string) =
+  # `dist` is first, to favor nearby matches
+  # `depth` is next, to favor nearby enclosing scopes among ties
+  # `sym.name.s` is last, to make the list ordered and deterministic among ties
+  (a.dist, a.depth, a.msg)
+
+proc `<`(a, b: SpellCandidate): bool =
+  a.toOrderTup < b.toOrderTup
+
+proc mustFixSpelling(c: PContext): bool {.inline.} =
+  result = c.config.spellSuggestMax != 0 and c.compilesContextId == 0
+    # don't slowdown inside compiles()
+
+proc fixSpelling(c: PContext, ident: PIdent, result: var string) =
+  ## when we cannot find the identifier, suggest nearby spellings
+  var list = initHeapQueue[SpellCandidate]()
+  let name0 = ident.s.nimIdentNormalize
+
+  for (sym, depth, isLocal) in allSyms(c):
+    let depth = -depth - 1
+    let dist = editDistance(name0, sym.name.s.nimIdentNormalize)
+    var msg: string = ""
+    msg.add "\n ($1, $2): '$3'" % [$dist, $depth, sym.name.s]
+    list.push SpellCandidate(dist: dist, depth: depth, msg: msg, sym: sym)
+
+  if list.len == 0: return
+  let e0 = list[0]
+  var
+    count = 0
+    last: PIdent = nil
+  while true:
+    # pending https://github.com/timotheecour/Nim/issues/373 use more efficient `itemsSorted`.
+    if list.len == 0: break
+    let e = list.pop()
+    if c.config.spellSuggestMax == spellSuggestSecretSauce:
+      const
+        minLengthForSuggestion = 4
+        maxCount = 3 # avoids ton of matches; three counts for equal distances
+      if e.dist > e0.dist or count >= maxCount or name0.len < minLengthForSuggestion: break
+    elif count >= c.config.spellSuggestMax: break
+    if count == 0:
+      result.add "\ncandidates (edit distance, scope distance); see '--spellSuggest': "
+    if e.sym.name != last:
+      result.add e.msg
+      count.inc
+      last = e.sym.name
+
+proc errorUseQualifier(c: PContext; info: TLineInfo; s: PSym; amb: var bool): PSym =
+  var err = "ambiguous identifier: '" & s.name.s & "'"
+  var i = 0
+  var ignoredModules = 0
+  result = nil
+  for candidate in importedItems(c, s.name):
+    if i == 0: err.add " -- use one of the following:\n"
+    else: err.add "\n"
+    err.add "  " & candidate.owner.name.s & "." & candidate.name.s
+    err.add ": " & typeToString(candidate.typ)
+    if candidate.kind == skModule:
+      inc ignoredModules
+    else:
+      result = candidate
+    inc i
+  if ignoredModules != i-1:
+    localError(c.config, info, errGenerated, err)
+    result = nil
+  else:
+    amb = false
 
 proc errorUseQualifier*(c: PContext; info: TLineInfo; s: PSym) =
-  var err = "Error: ambiguous identifier: '" & s.name.s & "'"
-  var ti: TIdentIter
-  var candidate = initIdentIter(ti, c.importTable.symbols, s.name)
+  var amb: bool = false
+  discard errorUseQualifier(c, info, s, amb)
+
+proc ambiguousIdentifierMsg*(candidates: seq[PSym], prefix = "use one of", indent = 0): string =
+  result = ""
+  for i in 0 ..< indent:
+    result.add(' ')
+  result.add "ambiguous identifier: '" & candidates[0].name.s & "'"
   var i = 0
-  while candidate != nil:
-    if i == 0: err.add " --use "
-    else: err.add " or "
-    err.add candidate.owner.name.s & "." & candidate.name.s
-    candidate = nextIdentIter(ti, c.importTable.symbols)
+  for candidate in candidates:
+    if i == 0: result.add " -- $1 the following:\n" % prefix
+    else: result.add "\n"
+    for i in 0 ..< indent:
+      result.add(' ')
+    result.add "  " & candidate.owner.name.s & "." & candidate.name.s
+    result.add ": " & typeToString(candidate.typ)
     inc i
-  localError(c.config, info, errGenerated, err)
 
-proc errorUndeclaredIdentifier*(c: PContext; info: TLineInfo; name: string) =
-  var err = "undeclared identifier: '" & name & "'"
-  if c.recursiveDep.len > 0:
-    err.add "\nThis might be caused by a recursive module dependency: "
-    err.add c.recursiveDep
-    # prevent excessive errors for 'nim check'
-    c.recursiveDep = nil
+proc errorUseQualifier*(c: PContext; info: TLineInfo; candidates: seq[PSym]) =
+  localError(c.config, info, errGenerated, ambiguousIdentifierMsg(candidates))
+
+proc ambiguousIdentifierMsg*(choices: PNode, indent = 0): string =
+  var candidates = newSeq[PSym](choices.len)
+  let prefix = if choices[0].typ.kind != tyProc: "use one of" else: "you need a helper proc to disambiguate"
+  for i, n in choices:
+    candidates[i] = n.sym
+  result = ambiguousIdentifierMsg(candidates, prefix, indent)
+
+proc errorUseQualifier*(c: PContext; info:TLineInfo; choices: PNode) =
+  localError(c.config, info, errGenerated, ambiguousIdentifierMsg(choices))
+
+proc errorUndeclaredIdentifier*(c: PContext; info: TLineInfo; name: string, extra = "") =
+  var err: string
+  if name == "_":
+    err = "the special identifier '_' is ignored in declarations and cannot be used"
+  else:
+    err = "undeclared identifier: '" & name & "'"
+    if "`gensym" in name:
+      err.add "; if declared in a template, this identifier may be inconsistently marked inject or gensym"
+    if extra.len != 0:
+      err.add extra
+    if c.recursiveDep.len > 0:
+      err.add "\nThis might be caused by a recursive module dependency:\n"
+      err.add c.recursiveDep
+      # prevent excessive errors for 'nim check'
+      c.recursiveDep = ""
   localError(c.config, info, errGenerated, err)
 
+proc errorUndeclaredIdentifierHint*(c: PContext; ident: PIdent; info: TLineInfo): PSym =
+  var extra = ""
+  if c.mustFixSpelling: fixSpelling(c, ident, extra)
+  errorUndeclaredIdentifier(c, info, ident.s, extra)
+  result = errorSym(c, ident, info)
+
 proc lookUp*(c: PContext, n: PNode): PSym =
   # Looks up a symbol. Generates an error in case of nil.
+  var amb = false
   case n.kind
   of nkIdent:
-    result = searchInScopes(c, n.ident).skipAlias(n, c.config)
-    if result == nil:
-      fixSpelling(n, n.ident, searchInScopes)
-      errorUndeclaredIdentifier(c, n.info, n.ident.s)
-      result = errorSym(c, n)
+    result = searchInScopes(c, n.ident, amb)
+    if result == nil: result = errorUndeclaredIdentifierHint(c, n.ident, n.info)
   of nkSym:
     result = n.sym
   of nkAccQuoted:
     var ident = considerQuotedIdent(c, n)
-    result = searchInScopes(c, ident).skipAlias(n, c.config)
-    if result == nil:
-      fixSpelling(n, ident, searchInScopes)
-      errorUndeclaredIdentifier(c, n.info, ident.s)
-      result = errorSym(c, n)
+    result = searchInScopes(c, ident, amb)
+    if result == nil: result = errorUndeclaredIdentifierHint(c, ident, n.info)
   else:
     internalError(c.config, n.info, "lookUp")
-    return
-  if contains(c.ambiguousSymbols, result.id):
-    errorUseQualifier(c, n.info, result)
+    return nil
+  if amb:
+    #contains(c.ambiguousSymbols, result.id):
+    result = errorUseQualifier(c, n.info, result, amb)
   when false:
     if result.kind == skStub: loadStub(result)
 
@@ -295,163 +640,277 @@ type
   TLookupFlag* = enum
     checkAmbiguity, checkUndeclared, checkModule, checkPureEnumFields
 
+const allExceptModule = {low(TSymKind)..high(TSymKind)} - {skModule, skPackage}
+
+proc lookUpCandidates*(c: PContext, ident: PIdent, filter: set[TSymKind],
+                       includePureEnum = false): seq[PSym] =
+  result = searchInScopesFilterBy(c, ident, filter)
+  if skEnumField in filter and (result.len == 0 or includePureEnum):
+    result.add allPureEnumFields(c, ident)
+
 proc qualifiedLookUp*(c: PContext, n: PNode, flags: set[TLookupFlag]): PSym =
-  const allExceptModule = {low(TSymKind)..high(TSymKind)}-{skModule,skPackage}
   case n.kind
   of nkIdent, nkAccQuoted:
+    var amb = false
     var ident = considerQuotedIdent(c, n)
     if checkModule in flags:
-      result = searchInScopes(c, ident).skipAlias(n, c.config)
+      result = searchInScopes(c, ident, amb)
+      if result == nil:
+        let candidates = allPureEnumFields(c, ident)
+        if candidates.len > 0:
+          result = candidates[0]
+          amb = candidates.len > 1
+          if amb and checkAmbiguity in flags:
+            errorUseQualifier(c, n.info, candidates)
     else:
-      result = searchInScopes(c, ident, allExceptModule).skipAlias(n, c.config)
-    if result == nil and checkPureEnumFields in flags:
-      result = strTableGet(c.pureEnumFields, ident)
+      let candidates = lookUpCandidates(c, ident, allExceptModule)
+      if candidates.len > 0:
+        result = candidates[0]
+        amb = candidates.len > 1
+        if amb and checkAmbiguity in flags:
+          errorUseQualifier(c, n.info, candidates)
+      else:
+        result = nil
     if result == nil and checkUndeclared in flags:
-      fixSpelling(n, ident, searchInScopes)
-      errorUndeclaredIdentifier(c, n.info, ident.s)
-      result = errorSym(c, n)
-    elif checkAmbiguity in flags and result != nil and
-        contains(c.ambiguousSymbols, result.id):
-      errorUseQualifier(c, n.info, result)
+      result = errorUndeclaredIdentifierHint(c, ident, n.info)
+    elif checkAmbiguity in flags and result != nil and amb:
+      result = errorUseQualifier(c, n.info, result, amb)
+    c.isAmbiguous = amb
   of nkSym:
     result = n.sym
-    if checkAmbiguity in flags and contains(c.ambiguousSymbols, result.id):
-      errorUseQualifier(c, n.info, n.sym)
+  of nkOpenSym:
+    result = qualifiedLookUp(c, n[0], flags)
   of nkDotExpr:
     result = nil
-    var m = qualifiedLookUp(c, n.sons[0], (flags*{checkUndeclared})+{checkModule})
+    var m = qualifiedLookUp(c, n[0], (flags * {checkUndeclared}) + {checkModule})
     if m != nil and m.kind == skModule:
       var ident: PIdent = nil
-      if n.sons[1].kind == nkIdent:
-        ident = n.sons[1].ident
-      elif n.sons[1].kind == nkAccQuoted:
-        ident = considerQuotedIdent(c, n.sons[1])
+      if n[1].kind == nkAccQuoted:
+        ident = considerQuotedIdent(c, n[1])
+      else:
+        # this includes sym and symchoice nodes, but since we are looking in
+        # a module, it shouldn't matter what was captured
+        ident = n[1].getPIdent
       if ident != nil:
         if m == c.module:
-          result = strTableGet(c.topLevelScope.symbols, ident).skipAlias(n, c.config)
+          var ti: TIdentIter = default(TIdentIter)
+          result = initIdentIter(ti, c.topLevelScope.symbols, ident)
+          if result != nil and nextIdentIter(ti, c.topLevelScope.symbols) != nil:
+            # another symbol exists with same name
+            c.isAmbiguous = true
         else:
-          result = strTableGet(m.tab, ident).skipAlias(n, c.config)
+          var amb: bool = false
+          if c.importModuleLookup.getOrDefault(m.name.id).len > 1:
+            result = errorUseQualifier(c, n.info, m, amb)
+          else:
+            result = someSymAmb(c.graph, m, ident, amb)
+            if amb: c.isAmbiguous = true
         if result == nil and checkUndeclared in flags:
-          fixSpelling(n.sons[1], ident, searchInScopes)
-          errorUndeclaredIdentifier(c, n.sons[1].info, ident.s)
-          result = errorSym(c, n.sons[1])
-      elif n.sons[1].kind == nkSym:
-        result = n.sons[1].sym
+          result = errorUndeclaredIdentifierHint(c, ident, n[1].info)
+      elif n[1].kind == nkSym:
+        result = n[1].sym
+        if result.owner != nil and result.owner != m and checkUndeclared in flags:
+          # dotExpr in templates can end up here
+          result = errorUndeclaredIdentifierHint(c, result.name, n[1].info)
       elif checkUndeclared in flags and
-           n.sons[1].kind notin {nkOpenSymChoice, nkClosedSymChoice}:
-        localError(c.config, n.sons[1].info, "identifier expected, but got: " &
-                   renderTree(n.sons[1]))
-        result = errorSym(c, n.sons[1])
+           n[1].kind notin {nkOpenSymChoice, nkClosedSymChoice}:
+        localError(c.config, n[1].info, "identifier expected, but got: " &
+                   renderTree(n[1]))
+        result = errorSym(c, n[1])
   else:
     result = nil
   when false:
     if result != nil and result.kind == skStub: loadStub(result)
 
 proc initOverloadIter*(o: var TOverloadIter, c: PContext, n: PNode): PSym =
+  if n.kind == nkOpenSym:
+    # maybe the logic in semexprs should be mirrored here instead
+    # for now it only seems this is called for `pickSym` in `getTypeIdent` 
+    return initOverloadIter(o, c, n[0])
+  o.importIdx = -1
+  o.marked = initIntSet()
   case n.kind
   of nkIdent, nkAccQuoted:
+    result = nil
     var ident = considerQuotedIdent(c, n)
-    o.scope = c.currentScope
+    var scope = c.currentScope
     o.mode = oimNoQualifier
     while true:
-      result = initIdentIter(o.it, o.scope.symbols, ident).skipAlias(n, c.config)
+      result = initIdentIter(o.it, scope.symbols, ident)
       if result != nil:
+        o.currentScope = scope
         break
       else:
-        o.scope = o.scope.parent
-        if o.scope == nil: break
+        scope = scope.parent
+        if scope == nil:
+          for i in 0..c.imports.high:
+            result = initIdentIter(o.mit, o.marked, c.imports[i], ident, c.graph)
+            if result != nil:
+              o.currentScope = nil
+              o.importIdx = i
+              return result
+          return nil
+
   of nkSym:
     result = n.sym
     o.mode = oimDone
   of nkDotExpr:
+    result = nil
     o.mode = oimOtherModule
-    o.m = qualifiedLookUp(c, n.sons[0], {checkUndeclared, checkModule})
+    o.m = qualifiedLookUp(c, n[0], {checkUndeclared, checkModule})
     if o.m != nil and o.m.kind == skModule:
       var ident: PIdent = nil
-      if n.sons[1].kind == nkIdent:
-        ident = n.sons[1].ident
-      elif n.sons[1].kind == nkAccQuoted:
-        ident = considerQuotedIdent(c, n.sons[1], n)
+      if n[1].kind == nkIdent:
+        ident = n[1].ident
+      elif n[1].kind == nkAccQuoted:
+        ident = considerQuotedIdent(c, n[1], n)
       if ident != nil:
         if o.m == c.module:
           # a module may access its private members:
           result = initIdentIter(o.it, c.topLevelScope.symbols,
-                                 ident).skipAlias(n, c.config)
+                                 ident)
           o.mode = oimSelfModule
         else:
-          result = initIdentIter(o.it, o.m.tab, ident).skipAlias(n, c.config)
+          result = initModuleIter(o.mit, c.graph, o.m, ident)
       else:
-        noidentError(c.config, n.sons[1], n)
-        result = errorSym(c, n.sons[1])
+        noidentError(c.config, n[1], n)
+        result = errorSym(c, n[1])
   of nkClosedSymChoice, nkOpenSymChoice:
     o.mode = oimSymChoice
     if n[0].kind == nkSym:
-      result = n.sons[0].sym
+      result = n[0].sym
     else:
       o.mode = oimDone
       return nil
     o.symChoiceIndex = 1
-    o.inSymChoice = initIntSet()
-    incl(o.inSymChoice, result.id)
-  else: discard
+    o.marked = initIntSet()
+    incl(o.marked, result.id)
+  else: result = nil
   when false:
     if result != nil and result.kind == skStub: loadStub(result)
 
 proc lastOverloadScope*(o: TOverloadIter): int =
   case o.mode
-  of oimNoQualifier: result = if o.scope.isNil: -1 else: o.scope.depthLevel
+  of oimNoQualifier:
+    result = if o.importIdx >= 0: 0
+             elif o.currentScope.isNil: -1
+             else: o.currentScope.depthLevel
   of oimSelfModule:  result = 1
   of oimOtherModule: result = 0
   else: result = -1
 
+proc nextOverloadIterImports(o: var TOverloadIter, c: PContext, n: PNode): PSym =
+  result = nil
+  assert o.currentScope == nil
+  var idx = o.importIdx+1
+  o.importIdx = c.imports.len # assume the other imported modules lack this symbol too
+  while idx < c.imports.len:
+    result = initIdentIter(o.mit, o.marked, c.imports[idx], o.it.name, c.graph)
+    if result != nil:
+      # oh, we were wrong, some other module had the symbol, so remember that:
+      o.importIdx = idx
+      break
+    inc idx
+
+proc symChoiceExtension(o: var TOverloadIter; c: PContext; n: PNode): PSym =
+  result = nil
+  assert o.currentScope == nil
+  while o.importIdx < c.imports.len:
+    result = initIdentIter(o.mit, o.marked, c.imports[o.importIdx], o.it.name, c.graph)
+    #while result != nil and result.id in o.marked:
+    #  result = nextIdentIter(o.it, o.marked, c.imports[o.importIdx])
+    if result != nil:
+      #assert result.id notin o.marked
+      return result
+    inc o.importIdx
+
 proc nextOverloadIter*(o: var TOverloadIter, c: PContext, n: PNode): PSym =
   case o.mode
   of oimDone:
     result = nil
   of oimNoQualifier:
-    if o.scope != nil:
-      result = nextIdentIter(o.it, o.scope.symbols).skipAlias(n, c.config)
+    if o.currentScope != nil:
+      assert o.importIdx < 0
+      result = nextIdentIter(o.it, o.currentScope.symbols)
       while result == nil:
-        o.scope = o.scope.parent
-        if o.scope == nil: break
-        result = initIdentIter(o.it, o.scope.symbols, o.it.name).skipAlias(n, c.config)
-        # BUGFIX: o.it.name <-> n.ident
+        o.currentScope = o.currentScope.parent
+        if o.currentScope != nil:
+          result = initIdentIter(o.it, o.currentScope.symbols, o.it.name)
+          # BUGFIX: o.it.name <-> n.ident
+        else:
+          o.importIdx = 0
+          if c.imports.len > 0:
+            result = initIdentIter(o.mit, o.marked, c.imports[o.importIdx], o.it.name, c.graph)
+            if result == nil:
+              result = nextOverloadIterImports(o, c, n)
+          break
+    elif o.importIdx < c.imports.len:
+      result = nextIdentIter(o.mit, o.marked, c.imports[o.importIdx], c.graph)
+      if result == nil:
+        result = nextOverloadIterImports(o, c, n)
     else:
       result = nil
   of oimSelfModule:
-    result = nextIdentIter(o.it, c.topLevelScope.symbols).skipAlias(n, c.config)
+    result = nextIdentIter(o.it, c.topLevelScope.symbols)
   of oimOtherModule:
-    result = nextIdentIter(o.it, o.m.tab).skipAlias(n, c.config)
+    result = nextModuleIter(o.mit, c.graph)
   of oimSymChoice:
-    if o.symChoiceIndex < sonsLen(n):
-      result = n.sons[o.symChoiceIndex].sym
-      incl(o.inSymChoice, result.id)
+    if o.symChoiceIndex < n.len:
+      result = n[o.symChoiceIndex].sym
+      incl(o.marked, result.id)
       inc o.symChoiceIndex
     elif n.kind == nkOpenSymChoice:
       # try 'local' symbols too for Koenig's lookup:
       o.mode = oimSymChoiceLocalLookup
-      o.scope = c.currentScope
-      result = firstIdentExcluding(o.it, o.scope.symbols,
-                                   n.sons[0].sym.name, o.inSymChoice).skipAlias(n, c.config)
+      o.currentScope = c.currentScope
+      result = firstIdentExcluding(o.it, o.currentScope.symbols,
+                                   n[0].sym.name, o.marked)
       while result == nil:
-        o.scope = o.scope.parent
-        if o.scope == nil: break
-        result = firstIdentExcluding(o.it, o.scope.symbols,
-                                     n.sons[0].sym.name, o.inSymChoice).skipAlias(n, c.config)
+        o.currentScope = o.currentScope.parent
+        if o.currentScope != nil:
+          result = firstIdentExcluding(o.it, o.currentScope.symbols,
+                                      n[0].sym.name, o.marked)
+        else:
+          o.importIdx = 0
+          result = symChoiceExtension(o, c, n)
+          break
+      if result != nil:
+        incl o.marked, result.id
+    else:
+      result = nil
   of oimSymChoiceLocalLookup:
-    result = nextIdentExcluding(o.it, o.scope.symbols, o.inSymChoice).skipAlias(n, c.config)
-    while result == nil:
-      o.scope = o.scope.parent
-      if o.scope == nil: break
-      result = firstIdentExcluding(o.it, o.scope.symbols,
-                                   n.sons[0].sym.name, o.inSymChoice).skipAlias(n, c.config)
+    if o.currentScope != nil:
+      result = nextIdentExcluding(o.it, o.currentScope.symbols, o.marked)
+      while result == nil:
+        o.currentScope = o.currentScope.parent
+        if o.currentScope != nil:
+          result = firstIdentExcluding(o.it, o.currentScope.symbols,
+                                      n[0].sym.name, o.marked)
+        else:
+          o.importIdx = 0
+          result = symChoiceExtension(o, c, n)
+          break
+      if result != nil:
+        incl o.marked, result.id
+
+    elif o.importIdx < c.imports.len:
+      result = nextIdentIter(o.mit, o.marked, c.imports[o.importIdx], c.graph)
+      #assert result.id notin o.marked
+      #while result != nil and result.id in o.marked:
+      #  result = nextIdentIter(o.it, c.imports[o.importIdx])
+      if result == nil:
+        inc o.importIdx
+        result = symChoiceExtension(o, c, n)
+    else:
+      result = nil
 
   when false:
     if result != nil and result.kind == skStub: loadStub(result)
 
 proc pickSym*(c: PContext, n: PNode; kinds: set[TSymKind];
               flags: TSymFlags = {}): PSym =
-  var o: TOverloadIter
+  result = nil
+  var o: TOverloadIter = default(TOverloadIter)
   var a = initOverloadIter(o, c, n)
   while a != nil:
     if a.kind in kinds and flags <= a.flags: