lib: Use Nix's static scope checking, fix error message, optimize

Nix can perform static scope checking, but whenever code is inside
a `with` expression, the analysis breaks down, because it can't
know statically what's in the attribute set whose attributes were
brought into scope. In those cases, Nix has to assume that
everything works out.

Except it doesnt. Removing `with` from lib/ revealed an undefined
variable in an error message.

If that doesn't convince you that we're better off without `with`,
I can tell you that this PR results in a 3% evaluation performance
improvement because Nix can look up local variables by index.
This adds up with applications like the module system.

Furthermore, removing `with` makes the binding site of each
variable obvious, which helps with comprehension.

lib/debug.nix

@@ -14,9 +14,25 @@
 */
 { lib }:
 let
-  inherit (builtins) trace isAttrs isList isInt
-          head substring attrNames;
-  inherit (lib) id elem isFunction;
+  inherit (lib)
+    isInt
+    attrNames
+    isList
+    isAttrs
+    substring
+    addErrorContext
+    attrValues
+    concatLists
+    concatStringsSep
+    const
+    elem
+    generators
+    head
+    id
+    isDerivation
+    isFunction
+    mapAttrs
+    trace;
 in
 
 rec {
@@ -94,7 +110,7 @@ rec {
        trace: { a = { b = {…}; }; }
        => null
    */
-  traceSeqN = depth: x: y: with lib;
+  traceSeqN = depth: x: y:
     let snip = v: if      isList  v then noQuotes "[…]" v
                   else if isAttrs v then noQuotes "{…}" v
                   else v;
@@ -149,7 +165,7 @@ rec {
   */
   runTests =
     # Tests to run
-    tests: lib.concatLists (lib.attrValues (lib.mapAttrs (name: test:
+    tests: concatLists (attrValues (mapAttrs (name: test:
     let testsToRun = if tests ? tests then tests.tests else [];
     in if (substring 0 4 name == "test" ||  elem name testsToRun)
        && ((testsToRun == []) || elem name tests.tests)
@@ -176,9 +192,9 @@ rec {
           + "and will be removed in the next release. "
           + "Please use more specific concatenation "
           + "for your uses (`lib.concat(Map)StringsSep`)." )
-    (lib.concatStringsSep "; " (map (x: "${x}=") (attrNames a)));
+    (concatStringsSep "; " (map (x: "${x}=") (attrNames a)));
 
-  showVal = with lib;
+  showVal =
     trace ( "Warning: `showVal` is deprecated "
           + "and will be removed in the next release, "
           + "please use `traceSeqN`" )
@@ -226,7 +242,7 @@ rec {
     trace ( "Warning: `addErrorContextToAttrs` is deprecated "
           + "and will be removed in the next release. "
           + "Please use `builtins.addErrorContext` directly." )
-    (lib.mapAttrs (a: v: lib.addErrorContext "while evaluating ${a}" v) attrs);
+    (mapAttrs (a: v: addErrorContext "while evaluating ${a}" v) attrs);
 
   # example: (traceCallXml "myfun" id 3) will output something like
   # calling myfun arg 1: 3 result: 3