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/strings.nix

@@ -8,7 +8,29 @@ in
 
 rec {
 
-  inherit (builtins) stringLength substring head tail isString replaceStrings;
+  inherit (builtins)
+    compareVersions
+    elem
+    elemAt
+    filter
+    fromJSON
+    head
+    isInt
+    isList
+    isString
+    match
+    parseDrvName
+    readFile
+    replaceStrings
+    split
+    storeDir
+    stringLength
+    substring
+    tail
+    toJSON
+    typeOf
+    unsafeDiscardStringContext
+    ;
 
   /* Concatenate a list of strings.
 
@@ -120,7 +142,7 @@ rec {
     subDir:
     # List of base paths
     paths:
-    concatStringsSep ":" (map (path: path + "/" + subDir) (builtins.filter (x: x != null) paths));
+    concatStringsSep ":" (map (path: path + "/" + subDir) (filter (x: x != null) paths));
 
   /* Construct a Unix-style search path by appending the given
      `subDir` to the specified `output` of each of the packages. If no
@@ -313,7 +335,7 @@ rec {
        escapeNixString "hello\${}\n"
        => "\"hello\\\${}\\n\""
   */
-  escapeNixString = s: escape ["$"] (builtins.toJSON s);
+  escapeNixString = s: escape ["$"] (toJSON s);
 
   /* Turn a string into an exact regular expression
 
@@ -337,7 +359,7 @@ rec {
   */
   escapeNixIdentifier = s:
     # Regex from https://github.com/NixOS/nix/blob/d048577909e383439c2549e849c5c2f2016c997e/src/libexpr/lexer.l#L91
-    if builtins.match "[a-zA-Z_][a-zA-Z0-9_'-]*" s != null
+    if match "[a-zA-Z_][a-zA-Z0-9_'-]*" s != null
     then s else escapeNixString s;
 
   # Obsolete - use replaceStrings instead.
@@ -466,7 +488,7 @@ rec {
        versionOlder "1.1" "1.1"
        => false
   */
-  versionOlder = v1: v2: builtins.compareVersions v2 v1 == 1;
+  versionOlder = v1: v2: compareVersions v2 v1 == 1;
 
   /* Return true if string v1 denotes a version equal to or newer than v2.
 
@@ -492,7 +514,7 @@ rec {
   */
   getName = x:
    let
-     parse = drv: (builtins.parseDrvName drv).name;
+     parse = drv: (parseDrvName drv).name;
    in if isString x
       then parse x
       else x.pname or (parse x.name);
@@ -509,7 +531,7 @@ rec {
   */
   getVersion = x:
    let
-     parse = drv: (builtins.parseDrvName drv).version;
+     parse = drv: (parseDrvName drv).version;
    in if isString x
       then parse x
       else x.version or (parse x.name);
@@ -527,7 +549,7 @@ rec {
     let
       components = splitString "/" url;
       filename = lib.last components;
-      name = builtins.head (splitString sep filename);
+      name = head (splitString sep filename);
     in assert name != filename; name;
 
   /* Create an --{enable,disable}-<feat> string that can be passed to
@@ -617,14 +639,14 @@ rec {
   */
   floatToString = float: let
     result = toString float;
-    precise = float == builtins.fromJSON result;
+    precise = float == fromJSON result;
   in if precise then result
     else lib.warn "Imprecise conversion from float to string ${result}" result;
 
   /* Check whether a value can be coerced to a string */
   isCoercibleToString = x:
-    builtins.elem (builtins.typeOf x) [ "path" "string" "null" "int" "float" "bool" ] ||
-    (builtins.isList x && lib.all isCoercibleToString x) ||
+    elem (typeOf x) [ "path" "string" "null" "int" "float" "bool" ] ||
+    (isList x && lib.all isCoercibleToString x) ||
     x ? outPath ||
     x ? __toString;
 
@@ -643,8 +665,8 @@ rec {
   isStorePath = x:
     if isCoercibleToString x then
       let str = toString x; in
-      builtins.substring 0 1 str == "/"
-      && dirOf str == builtins.storeDir
+      substring 0 1 str == "/"
+      && dirOf str == storeDir
     else
       false;
 
@@ -662,8 +684,8 @@ rec {
   */
   # Obviously, it is a bit hacky to use fromJSON this way.
   toInt = str:
-    let may_be_int = builtins.fromJSON str; in
-    if builtins.isInt may_be_int
+    let may_be_int = fromJSON str; in
+    if isInt may_be_int
     then may_be_int
     else throw "Could not convert ${str} to int.";
 
@@ -685,10 +707,10 @@ rec {
   readPathsFromFile = lib.warn "lib.readPathsFromFile is deprecated, use a list instead"
     (rootPath: file:
       let
-        lines = lib.splitString "\n" (builtins.readFile file);
+        lines = lib.splitString "\n" (readFile file);
         removeComments = lib.filter (line: line != "" && !(lib.hasPrefix "#" line));
         relativePaths = removeComments lines;
-        absolutePaths = builtins.map (path: rootPath + "/${path}") relativePaths;
+        absolutePaths = map (path: rootPath + "/${path}") relativePaths;
       in
         absolutePaths);
 
@@ -702,7 +724,7 @@ rec {
        fileContents ./version
        => "1.0"
   */
-  fileContents = file: removeSuffix "\n" (builtins.readFile file);
+  fileContents = file: removeSuffix "\n" (readFile file);
 
 
   /* Creates a valid derivation name from a potentially invalid one.
@@ -720,13 +742,13 @@ rec {
   sanitizeDerivationName = string: lib.pipe string [
     # Get rid of string context. This is safe under the assumption that the
     # resulting string is only used as a derivation name
-    builtins.unsafeDiscardStringContext
+    unsafeDiscardStringContext
     # Strip all leading "."
-    (x: builtins.elemAt (builtins.match "\\.*(.*)" x) 0)
+    (x: elemAt (match "\\.*(.*)" x) 0)
     # Split out all invalid characters
     # https://github.com/NixOS/nix/blob/2.3.2/src/libstore/store-api.cc#L85-L112
     # https://github.com/NixOS/nix/blob/2242be83c61788b9c0736a92bb0b5c7bbfc40803/nix-rust/src/store/path.rs#L100-L125
-    (builtins.split "[^[:alnum:]+._?=-]+")
+    (split "[^[:alnum:]+._?=-]+")
     # Replace invalid character ranges with a "-"
     (concatMapStrings (s: if lib.isList s then "-" else s))
     # Limit to 211 characters (minus 4 chars for ".drv")