Easy way to defer type errors (implements #8353)

Added load! and reload! commands, effectively setting
"-fdefer-type-errors" before loading a file and
unsetting it after loading if it has not been set before.

Differential Revision: https://phabricator.haskell.org/D960

2 files changed, 34 insertions, 11 deletions

diff --git a/docs/users_guide/7.12.1-notes.xml b/docs/users_guide/7.12.1-notes.xml
index f217b91cdd..dc191d2638 100644
--- a/docs/users_guide/7.12.1-notes.xml
+++ b/docs/users_guide/7.12.1-notes.xml
@@ -101,6 +101,11 @@
                     commands now take an optional count allowing the user to move forward or
                     backward in history several steps at a time.
                </para>
+               <para>
+                    Added commands <literal>:load!</literal> and <literal>:reload!</literal>,
+                    effectively setting "-fdefer-type-errors" before loading a module and
+                    unsetting it after loading if it has not been set before (#8353).
+               </para>
            </listitem>
        </itemizedlist>
     </sect3>
diff --git a/docs/users_guide/ghci.xml b/docs/users_guide/ghci.xml
index a1271e1ac1..399cda90ea 100644
--- a/docs/users_guide/ghci.xml
+++ b/docs/users_guide/ghci.xml
@@ -674,13 +674,13 @@ Prelude>
       <title>What's really in scope at the prompt?</title>
 
       <para>When you type an expression at the prompt, what
-      identifiers and types are in scope?  
+      identifiers and types are in scope?
       GHCi provides a flexible
       way to control exactly how the context for an expression is
       constructed:
   <itemizedlist>
   <listitem><para>
-        The <literal>:load</literal>, <literal>:add</literal>, 
+        The <literal>:load</literal>, <literal>:add</literal>,
         and <literal>:reload</literal> commands (<xref linkend="ghci-load-scope"/>).
    </para></listitem>
   <listitem><para>
@@ -702,8 +702,8 @@ Prelude>
    <sect3 id="ghci-load-scope">
    <title>The effect of <literal>:load</literal> on what is in scope</title>
       <para>
-      The <literal>:load</literal>, <literal>:add</literal>, and <literal>:reload</literal> 
-       commands (<xref linkend="loading-source-files"/> 
+      The <literal>:load</literal>, <literal>:add</literal>, and <literal>:reload</literal>
+       commands (<xref linkend="loading-source-files"/>
       and <xref linkend="ghci-compiled"/>) affect the top-level scope.
       Let's start with the simple cases; when you start
       GHCi the prompt looks like this:
@@ -830,7 +830,7 @@ Prelude System.IO Map>
       <title>Controlling what is in scope with the <literal>:module</literal> command</title>
 
       <para>Another way to manipulate the scope is to use the
-      <literal>:module</literal> command, whose syntax is this: 
+      <literal>:module</literal> command, whose syntax is this:
 
 <screen>
 :module <optional>+|-</optional> <optional>*</optional><replaceable>mod<subscript>1</subscript></replaceable> ... <optional>*</optional><replaceable>mod<subscript>n</subscript></replaceable>
@@ -881,7 +881,7 @@ Prelude System.IO Map>
         <literal>:load</literal></title>
 
         <para>It might seem that <literal>:module</literal>/<literal>import</literal> and
-        <literal>:load</literal>/<literal>:add</literal>/<literal>:reload</literal> 
+        <literal>:load</literal>/<literal>:add</literal>/<literal>:reload</literal>
         do similar things: you can use both
         to bring a module into scope.  However, there is a very important
         difference.  GHCi is concerned with two sets of modules:</para>
@@ -907,7 +907,7 @@ Prelude System.IO Map>
           </listitem>
         </itemizedlist>
 
-        <para>You can add a module to the scope (via <literal>:module</literal> 
+        <para>You can add a module to the scope (via <literal>:module</literal>
            or <literal>import</literal>)
           only if either (a) it is loaded, or
           (b) it is a module from a package that GHCi knows about.
@@ -2627,7 +2627,7 @@ T Int :: * -> *
 
       <varlistentry>
         <term>
-          <literal>:load</literal> <optional><literal>*</literal></optional><replaceable>module</replaceable> ...
+          <literal>:load</literal><optional><literal>!</literal></optional> <optional><literal>*</literal></optional><replaceable>module</replaceable> ...
           <indexterm><primary><literal>:load</literal></primary></indexterm>
         </term>
         <listitem>
@@ -2649,6 +2649,15 @@ T Int :: * -> *
           byte-code.  Using the <literal>*</literal> prefix forces a
           module to be loaded as byte-code.</para>
 
+          <para>Adding the optional "<literal>!</literal>" turns type
+          errors into warnings while loading. This allows to use the
+          portions of the module that are correct, even if there are
+          type errors in some definitions. Effectively, the
+          "-fdefer-type-errors" flag is set before loading and unset
+          after loading if the flag has not already been set
+          before. See <xref linkend="defer-type-errors" /> for further
+          motivation and details.</para>
+
           <para>After a <literal>:load</literal> command, the current
           context is set to:</para>
 
@@ -2785,7 +2794,7 @@ bar
 
       <varlistentry>
         <term>
-          <literal>:reload</literal>
+          <literal>:reload</literal><optional><literal>!</literal></optional>
           <indexterm><primary><literal>:reload</literal></primary></indexterm>
         </term>
         <listitem>
@@ -2794,6 +2803,15 @@ bar
           or any dependent module, has changed.  Note that this may
           entail loading new modules, or dropping modules which are no
           longer indirectly required by the target.</para>
+
+          <para>Adding the optional "<literal>!</literal>" turns type
+          errors into warnings while loading. This allows to use the
+          portions of the module that are correct, even if there are
+          type errors in some definitions. Effectively, the
+          "-fdefer-type-errors" flag is set before loading and unset
+          after loading if the flag has not already been set
+          before. See <xref linkend="defer-type-errors" /> for further
+          motivation and details.</para>
         </listitem>
       </varlistentry>
 
@@ -3302,7 +3320,7 @@ Prelude> :set -fno-warn-incomplete-patterns -XNoMultiParamTypeClasses
       <title>Setting options for interactive evaluation only</title>
 
       <para>
-        GHCi actually maintains <emphasis>two</emphasis> sets of options: 
+        GHCi actually maintains <emphasis>two</emphasis> sets of options:
 <itemizedlist>
 <listitem><para>
   The <emphasis>loading options</emphasis> apply when loading modules
@@ -3317,7 +3335,7 @@ The <literal>:set</literal> command modifies both, but there is
       </para>
 
       <para>
-        It is often useful to change the interactive options, 
+        It is often useful to change the interactive options,
         without having that option apply to loaded modules
         too.  For example
 <screen>