Added utility command ‘nix-instantiate --find-file’ to look up a file in Nix's search path

2 files changed, 26 insertions, 0 deletions

diff --git a/doc/manual/nix-instantiate.xml b/doc/manual/nix-instantiate.xml
index a659ee730484..7e6120852f09 100644
--- a/doc/manual/nix-instantiate.xml
+++ b/doc/manual/nix-instantiate.xml
@@ -36,6 +36,7 @@
           <option>--eval-only</option>
           <arg><option>--strict</option></arg>
         </arg>
+        <arg choice='plain'><option>--find-file</option></arg>
       </group>
       <arg><option>--xml</option></arg>
     </arg>
@@ -100,6 +101,19 @@ policies.</para>
     
   </varlistentry>
 
+  <varlistentry><term><option>--find-file</option></term>
+  
+    <listitem><para>Look up the given files in Nix’s search path (as
+    specified by the <envar>NIX_PATH</envar> environment variable).
+    If found, print the corresponding absolute paths on standard
+    output.  For instance, if <envar>NIX_PATH</envar> is
+    <literal>nixpkgs=/home/alice/nixpkgs</literal>, then
+    <literal>nix-instantiate --find-file nixpkgs/default.nix</literal>
+    will print
+    <literal>/home/alice/nixpkgs/default.nix</literal>.</para></listitem>
+    
+  </varlistentry>
+      
   <varlistentry><term><option>--xml</option></term>
 
     <listitem><para>When used with <option>--parse-only</option> and
diff --git a/src/nix-instantiate/nix-instantiate.cc b/src/nix-instantiate/nix-instantiate.cc
index 8f3a290f3a6a..adc8ca623807 100644
--- a/src/nix-instantiate/nix-instantiate.cc
+++ b/src/nix-instantiate/nix-instantiate.cc
@@ -79,6 +79,7 @@ void run(Strings args)
     EvalState state;
     Strings files;
     bool readStdin = false;
+    bool findFile = false;
     bool evalOnly = false;
     bool parseOnly = false;
     bool xmlOutput = false;
@@ -100,6 +101,8 @@ void run(Strings args)
             readOnlyMode = true;
             parseOnly = evalOnly = true;
         }
+        else if (arg == "--find-file")
+            findFile = true;
         else if (arg == "--attr" || arg == "-A") {
             if (i == args.end())
                 throw UsageError("`--attr' requires an argument");
@@ -130,6 +133,15 @@ void run(Strings args)
 
     if (attrPaths.empty()) attrPaths.push_back("");
 
+    if (findFile) {
+        foreach (Strings::iterator, i, files) {
+            Path p = state.findFile(*i);
+            if (p == "") throw Error(format("unable to find `%1%'") % *i);
+            std::cout << p << std::endl;
+        }
+        return;
+    }
+
     store = openStore();
 
     if (readStdin) {