Make it work

README.md

@@ -32,7 +32,7 @@ want total control.
 stdenv.mkDerivation {
   name = "my-project";
   src = nix-filter {
-    src = ./.;
+    path = ./.;
     allow = [
       "src" # strings are automatically converted to ./src filter
       ./package.json # paths are automatically converted to path filters

default.nix

@@ -1,17 +1,4 @@
 # This is a pure and self-contained library
-let
-  hasSuffix =
-    # Suffix to check for
-    suffix:
-    # Input string
-    content:
-    let
-      lenContent = builtins.length content;
-      lenSuffix = builtins.length suffix;
-    in
-    lenContent >= lenSuffix &&
-    builtins.substring (lenContent - lenSuffix) lenContent content == suffix;
-in
 rec {
   # Default to filter when calling this lib.
   __functor = self: filter;
@@ -37,12 +24,13 @@ rec {
       # sub-folders.
       toMatcher = f:
         let
+          # Push these here to memoize the result
           path_ = toString f;
           path__ = "${toString path}/${f}";
         in
         if builtins.isFunction f then f
-        else if builtins.isPath f then (path: type: path_ == toString path)
-        else if builtins.isString f then (path: type: path__ == toString path)
+        else if builtins.isPath f then (path: _: path_ == path)
+        else if builtins.isString f then (path: _: path__ == path)
         else
           throw "Unsupported type ${builtins.typeOf f}";
 
@@ -57,7 +45,30 @@ rec {
     };
 
   # Match paths with the given extension
-  byExt = ext:
+  matchExt = ext:
     path: type:
-      (hasSuffix ".${ext} " path);
+      _hasSuffix ".${ext}" path;
+
+  # Used to debug matchers.
+  debugMatch = label: fn:
+    path: type:
+      let
+        ret = fn path type;
+      in
+      builtins.trace "label=${label} path=${path} type=${type} ret=${toString ret}"
+        ret;
+
+  # Lib stuff
+
+  _hasSuffix =
+    # Suffix to check for
+    suffix:
+    # Input string
+    content:
+    let
+      lenContent = builtins.stringLength content;
+      lenSuffix = builtins.stringLength suffix;
+    in
+    lenContent >= lenSuffix
+    && builtins.substring (lenContent - lenSuffix) lenContent content == suffix;
 }

tests/default.nix

@@ -0,0 +1,23 @@
+let
+  nix-filter = import ../.;
+in
+{
+  all = nix-filter {
+    path = ./demo1;
+  };
+
+  without-readme = nix-filter {
+    path = ./demo1;
+    deny = [
+      "README.md"
+    ];
+  };
+
+  with-matchExt = nix-filter {
+    path = ./demo1;
+    allow = [
+      "package.json"
+      (nix-filter.matchExt "js")
+    ];
+  };
+}