nix-instantiate: Add a flag --expr / -E to read expressions from the command line

This is basically a shortcut for ‘echo 'expr...' | nix-instantiate -’.
Also supported by nix-build and nix-shell.

doc/manual/nix-build.xml

@@ -164,6 +164,16 @@ $ nix-build '<nixpkgs>' -A openssl.man
 </screen>
 This will create a symlink <literal>result-man</literal>.</para>
 
+<para>Build a Nix expression given on the command line:
+
+<screen>
+$ nix-build -E 'with import &lt;nixpkgs> { }; runCommand "foo" { } "echo bar > $out"'
+$ cat ./result
+bar
+</screen>
+
+</para>
+
 </refsection>
 
 

doc/manual/nix-instantiate.xml

@@ -18,7 +18,15 @@
 <refsynopsisdiv>
   <cmdsynopsis>
     <command>nix-instantiate</command>
-    <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="opt-common-syn.xml#xmlns(db=http://docbook.org/ns/docbook)xpointer(/db:nop/*)" />
+    <group>
+      <arg choice='plain'><option>--parse-only</option></arg>
+      <arg choice='plain'>
+        <option>--eval-only</option>
+        <arg><option>--strict</option></arg>
+        <arg><option>--xml</option></arg>
+      </arg>
+    </group>
+    <arg><option>--read-write-mode</option></arg>
     <arg><option>--arg</option> <replaceable>name</replaceable> <replaceable>value</replaceable></arg>
     <arg>
       <group choice='req'>
@@ -29,18 +37,14 @@
     </arg>
     <arg><option>--add-root</option> <replaceable>path</replaceable></arg>
     <arg><option>--indirect</option></arg>
-    <arg>
     <group choice='req'>
-        <arg choice='plain'><option>--parse-only</option></arg>
-        <arg choice='plain'>
-          <option>--eval-only</option>
-          <arg><option>--strict</option></arg>
-          <arg><option>--read-write-mode</option></arg>
-        </arg>
-        <arg choice='plain'><option>--find-file</option></arg>
+      <arg choice='plain'><option>--expr</option></arg>
+      <arg choice='plain'><option>-E</option></arg>
     </group>
-      <arg><option>--xml</option></arg>
-    </arg>
+    <arg choice='plain' rep='repeat'><replaceable>files</replaceable></arg>
+    <sbr/>
+    <command>nix-instantiate</command>
+    <arg choice='plain'><option>--file-file</option></arg>
     <arg choice='plain' rep='repeat'><replaceable>files</replaceable></arg>
   </cmdsynopsis>
 </refsynopsisdiv>
@@ -50,8 +54,8 @@
 
 <para>The command <command>nix-instantiate</command> generates <link
 linkend="gloss-derivation">store derivations</link> from (high-level)
-Nix expressions.  It loads and evaluates the Nix expressions in each
-of <replaceable>files</replaceable> (which defaults to
+Nix expressions.  It evaluates the Nix expressions in each of
+<replaceable>files</replaceable> (which defaults to
 <replaceable>./default.nix</replaceable>).  Each top-level expression
 should evaluate to a derivation, a list of derivations, or a set of
 derivations.  The paths of the resulting store derivations are printed
@@ -61,12 +65,6 @@ on standard output.</para>
 <literal>-</literal>, then a Nix expression will be read from standard
 input.</para>
 
-<para>Most users and developers don’t need to use this command
-(<command>nix-env</command> and <command>nix-build</command> perform
-store derivation instantiation from Nix expressions automatically).
-It is most commonly used for implementing new deployment
-policies.</para>
-
 <para condition="manual">See also <xref linkend="sec-common-options"
 /> for a list of common options.</para>
 
@@ -86,7 +84,6 @@ policies.</para>
 
   </varlistentry>
 
-    
   <varlistentry><term><option>--parse-only</option></term>
 
     <listitem><para>Just parse the input files, and print their
@@ -180,19 +177,34 @@ dr-xr-xr-x    2 eelco    users        4096 1970-01-01 01:00 lib
 
 </para>
 
+<para>You can also give a Nix expression on the command line:
+
+<screen>
+$ nix-instantiate -E 'with import &lt;nixpkgs> { }; hello'
+/nix/store/j8s4zyv75a724q38cb0r87rlczaiag4y-hello-2.8.drv
+</screen>
+
+This is equivalent to:
+
+<screen>
+$ nix-instantiate '&lt;nixpkgs>' -A hello
+</screen>
+
+</para>
+
 <para>Parsing and evaluating Nix expressions:
 
 <screen>
-$ echo '"foo" + "bar"' | nix-instantiate --parse-only -
-OpPlus(Str("foo"),Str("bar"))
+$ nix-instantiate --parse-only -E '1 + 2'
+1 + 2
 
-$ echo '"foo" + "bar"' | nix-instantiate --eval-only -
-Str("foobar")
+$ nix-instantiate --eval-only -E '1 + 2'
+3
 
-$ echo '"foo" + "bar"' | nix-instantiate --eval-only --xml -
+$ nix-instantiate --eval-only --xml -E '1 + 2'
 <![CDATA[<?xml version='1.0' encoding='utf-8'?>
 <expr>
-  <string value="foobar" />
+  <int value="3" />
 </expr>]]></screen>
 
 </para>
@@ -200,7 +212,7 @@ $ echo '"foo" + "bar"' | nix-instantiate --eval-only --xml -
 <para>The difference between non-strict and strict evaluation:
 
 <screen>
-$ echo 'rec { x = "foo"; y = x; }' | nix-instantiate --eval-only --xml -
+$ nix-instantiate --eval-only --xml -E 'rec { x = "foo"; y = x; }'
 <replaceable>...</replaceable><![CDATA[
   <attr name="x">
     <string value="foo" />
@@ -214,7 +226,7 @@ Note that <varname>y</varname> is left unevaluated (the XML
 representation doesn’t attempt to show non-normal forms).
 
 <screen>
-$ echo 'rec { x = "foo"; y = x; }' | nix-instantiate --eval-only --xml --strict -
+$ nix-instantiate --eval-only --xml --strict -E 'rec { x = "foo"; y = x; }'
 <replaceable>...</replaceable><![CDATA[
   <attr name="x">
     <string value="foo" />

doc/manual/nix-shell.xml

@@ -61,11 +61,11 @@ the derivation attribute
 <programlisting>
 shellHook =
   ''
-    echo "Hello shell!"
+    echo "Hello shell"
   '';
 </programlisting>
 
-will cause <command>nix-shell</command> to print <literal>Hello shell!</literal>.</para>
+will cause <command>nix-shell</command> to print <literal>Hello shell</literal>.</para>
 
 </refsection>
 
@@ -132,11 +132,11 @@ interactive shell in which to build it:
 
 <screen>
 $ nix-shell '&lt;nixpkgs>' -A pan
-$ unpackPhase
-$ cd pan-*
-$ configurePhase
-$ buildPhase
-$ ./pan/gui/pan
+[nix-shell]$ unpackPhase
+[nix-shell]$ cd pan-*
+[nix-shell]$ configurePhase
+[nix-shell]$ buildPhase
+[nix-shell]$ ./pan/gui/pan
 </screen>
 
 To clear the environment first, and do some additional automatic
@@ -147,6 +147,14 @@ $ nix-shell '&lt;nixpkgs>' -A pan --pure \
     --command 'export NIX_DEBUG=1; export NIX_CORES=8; return'
 </screen>
 
+Nix expressions can also be given on the command line.  For instance,
+the following starts a shell containing the packages
+<literal>sqlite</literal> and <literal>libX11</literal>:
+
+<screen>
+$ nix-shell -E 'with import &lt;nixpkgs> { }; runCommand "dummy" { buildInputs = [ sqlite xorg.libX11 ]; } ""'
+</screen>
+
 </para>
 
 </refsection>

doc/manual/opt-common.xml

@@ -310,10 +310,10 @@
 <varlistentry xml:id="opt-attr"><term><option>--attr</option> / <option>-A</option>
 <replaceable>attrPath</replaceable></term>
 
-  <listitem><para>In <command>nix-env</command>,
-  <command>nix-instantiate</command> and <command>nix-build</command>,
-  <option>--attr</option> allows you to select an attribute from the
-  top-level Nix expression being evaluated.  The <emphasis>attribute
+  <listitem><para>Select an attribute from the top-level Nix
+  expression being evaluated.  (<command>nix-env</command>,
+  <command>nix-instantiate</command>, <command>nix-build</command> and
+  <command>nix-shell</command> only.)  The <emphasis>attribute
   path</emphasis> <replaceable>attrPath</replaceable> is a sequence of
   attribute names separated by dots.  For instance, given a top-level
   Nix expression <replaceable>e</replaceable>, the attribute path
@@ -333,6 +333,16 @@
 </varlistentry>
 
 
+<varlistentry><term><option>--expr</option> / <option>-E</option></term>
+
+  <listitem><para>Interpret the command line arguments as a list of
+  Nix expressions to be parsed and evaluated, rather than as a list
+  of file names of Nix expressions.
+  (<command>nix-instantiate</command>, <command>nix-build</command>
+  and <command>nix-shell</command> only.)</para></listitem>
+
+</varlistentry>
+
 <varlistentry><term><option>--show-trace</option></term>
 
   <listitem><para>Causes Nix to print out a stack trace in case of Nix

scripts/nix-build.in

@@ -11,6 +11,7 @@ my $dryRun = 0;
 my $verbose = 0;
 my $runEnv = $0 =~ /nix-shell$/;
 my $pure = 0;
+my $fromArgs = 0;
 
 my @instArgs = ();
 my @buildArgs = ();
@@ -49,7 +50,7 @@ for (my $n = 0; $n < scalar @ARGV; $n++) {
         $drvLink = "./derivation";
     }
 
-    elsif ($arg eq "--no-out-link" or $arg eq "--no-link") {
+    elsif ($arg eq "--no-out-link" || $arg eq "--no-link") {
         $outLink = "$tmpDir/result";
     }
 
@@ -59,13 +60,13 @@ for (my $n = 0; $n < scalar @ARGV; $n++) {
         $drvLink = $ARGV[$n];
     }
 
-    elsif ($arg eq "--out-link" or $arg eq "-o") {
+    elsif ($arg eq "--out-link" || $arg eq "-o") {
         $n++;
         die "$0: `$arg' requires an argument\n" unless $n < scalar @ARGV;
         $outLink = $ARGV[$n];
     }
 
-    elsif ($arg eq "--attr" or $arg eq "-A" or $arg eq "-I") {
+    elsif ($arg eq "--attr" || $arg eq "-A" || $arg eq "-I") {
         $n++;
         die "$0: `$arg' requires an argument\n" unless $n < scalar @ARGV;
         push @instArgs, ($arg, $ARGV[$n]);
@@ -91,7 +92,7 @@ for (my $n = 0; $n < scalar @ARGV; $n++) {
         $n += 2;
     }
 
-    elsif ($arg eq "--max-jobs" or $arg eq "-j" or $arg eq "--max-silent-time" or $arg eq "--log-type" or $arg eq "--cores" or $arg eq "--timeout") {
+    elsif ($arg eq "--max-jobs" || $arg eq "-j" || $arg eq "--max-silent-time" || $arg eq "--log-type" || $arg eq "--c||es" || $arg eq "--timeout") {
         $n++;
         die "$0: `$arg' requires an argument\n" unless $n < scalar @ARGV;
         push @buildArgs, ($arg, $ARGV[$n]);
@@ -110,7 +111,7 @@ for (my $n = 0; $n < scalar @ARGV; $n++) {
         @exprs = ("-");
     }
 
-    elsif ($arg eq "--verbose" or substr($arg, 0, 2) eq "-v") {
+    elsif ($arg eq "--verbose" || substr($arg, 0, 2) eq "-v") {
         push @buildArgs, $arg;
         push @instArgs, $arg;
         $verbose = 1;
@@ -144,6 +145,11 @@ for (my $n = 0; $n < scalar @ARGV; $n++) {
     elsif ($arg eq "--pure") { $pure = 1; }
     elsif ($arg eq "--impure") { $pure = 0; }
 
+    elsif ($arg eq "--expr" || $arg eq "-E") {
+        $fromArgs = 1;
+        push @instArgs, "--expr";
+    }
+
     elsif (substr($arg, 0, 1) eq "-") {
         push @buildArgs, $arg;
     }
@@ -153,8 +159,10 @@ for (my $n = 0; $n < scalar @ARGV; $n++) {
     }
 }
 
+if (!$fromArgs) {
     @exprs = ("shell.nix") if scalar @exprs == 0 && $runEnv && -e "shell.nix";
     @exprs = ("default.nix") if scalar @exprs == 0;
+}
 
 $ENV{'IN_NIX_SHELL'} = 1 if $runEnv;
 

src/nix-instantiate/nix-instantiate.cc

@@ -89,6 +89,7 @@ void run(Strings args)
     EvalState state;
     Strings files;
     bool readStdin = false;
+    bool fromArgs = false;
     bool findFile = false;
     bool evalOnly = false;
     bool parseOnly = false;
@@ -104,6 +105,8 @@ void run(Strings args)
 
         if (arg == "-")
             readStdin = true;
+        else if (arg == "--expr" || arg == "-E")
+            fromArgs = true;
         else if (arg == "--eval-only")
             evalOnly = true;
         else if (arg == "--read-write-mode")
@@ -162,11 +165,13 @@ void run(Strings args)
         Expr * e = parseStdin(state);
         processExpr(state, attrPaths, parseOnly, strict, autoArgs,
             evalOnly, xmlOutput, xmlOutputSourceLocation, e);
-    } else if (files.empty())
+    } else if (files.empty() && !fromArgs)
         files.push_back("./default.nix");
 
     foreach (Strings::iterator, i, files) {
-        Expr * e = state.parseExprFromFile(resolveExprPath(lookupFileArg(state, *i)));
+        Expr * e = fromArgs
+            ? state.parseExprFromString(*i, absPath("."))
+            : state.parseExprFromFile(resolveExprPath(lookupFileArg(state, *i)));
         processExpr(state, attrPaths, parseOnly, strict, autoArgs,
             evalOnly, xmlOutput, xmlOutputSourceLocation, e);
     }