Package keys (for linking/type equality) separated from package IDs.

This patch set makes us no longer assume that a package key is a human
readable string, leaving Cabal free to "do whatever it wants" to allocate
keys; we'll look up the PackageId in the database to display to the user.
This also means we have a new level of qualifier decisions to make at the
package level, and rewriting some Safe Haskell error reporting code to DTRT.

Additionally, we adjust the build system to use a new ghc-cabal output
Make variable PACKAGE_KEY to determine library names and other things,
rather than concatenating PACKAGE/VERSION as before.

Adds a new `-this-package-key` flag to subsume the old, erroneously named
`-package-name` flag, and `-package-key` to select packages by package key.

RFC: The md5 hashes are pretty tough on the eye, as far as the file
system is concerned :(

ToDo: safePkg01 test had its output updated, but the fix is not really right:
the rest of the dependencies are truncated due to the fact the we're only
grepping a single line, but ghc-pkg is wrapping its output.

ToDo: In a later commit, update all submodules to stop using -package-name
and use -this-package-key.  For now, we don't do it to avoid submodule
explosion.

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

Test Plan: validate

Reviewers: simonpj, simonmar, hvr, austin

Subscribers: simonmar, relrod, carter

Differential Revision: https://phabricator.haskell.org/D80

2 files changed, 8 insertions, 12 deletions

diff --git a/docs/users_guide/flags.xml b/docs/users_guide/flags.xml
index 1dd224a611..8381ca1254 100644
--- a/docs/users_guide/flags.xml
+++ b/docs/users_guide/flags.xml
@@ -590,7 +590,7 @@
         </thead>
         <tbody>
           <row>
-            <entry><option>-package-name</option> <replaceable>P</replaceable></entry>
+            <entry><option>-this-package-key</option> <replaceable>P</replaceable></entry>
             <entry>Compile to be part of package <replaceable>P</replaceable></entry>
             <entry>static</entry>
             <entry>-</entry>
diff --git a/docs/users_guide/packages.xml b/docs/users_guide/packages.xml
index 62b4e96bfd..50549b409c 100644
--- a/docs/users_guide/packages.xml
+++ b/docs/users_guide/packages.xml
@@ -258,19 +258,15 @@ exposed-modules: Network.BSD,
       </varlistentry>
 
       <varlistentry>
-        <term><option>-package-name</option> <replaceable>foo</replaceable>
-        <indexterm><primary><option>-package-name</option></primary>
+        <term><option>-this-package-key</option> <replaceable>foo</replaceable>
+        <indexterm><primary><option>-this-package-key</option></primary>
           </indexterm></term>
         <listitem>
           <para>Tells GHC the the module being compiled forms part of
-            package <replaceable>foo</replaceable>.
+            package key <replaceable>foo</replaceable>; internally, these
+            keys are used to determine type equality and linker symbols.
             If this flag is omitted (a very common case) then the
             default package <literal>main</literal> is assumed.</para>
-            <para>Note: the argument to <option>-package-name</option>
-              should be the full
-              package <literal>name-version</literal> for the package.
-              For example:
-            <literal>-package mypkg-1.2</literal>.</para>
         </listitem>
       </varlistentry>
 
@@ -328,7 +324,7 @@ exposed-modules: Network.BSD,
 
   <para>Every complete Haskell program must define <literal>main</literal> in
    module <literal>Main</literal>
-   in package <literal>main</literal>.   (Omitting the <option>-package-name</option> flag compiles
+   in package <literal>main</literal>.   (Omitting the <option>-this-package-key</option> flag compiles
    code for package <literal>main</literal>.) Failure to do so leads to a somewhat obscure
    link-time error of the form:
 <programlisting>
@@ -1170,8 +1166,8 @@ ghc-pkg dot | tred | dot -Tpdf >pkgs.pdf
     </itemizedlist>
 
      <para>To compile a module which is to be part of a new package,
-      use the <literal>-package-name</literal> option (<xref linkend="using-packages"/>).
-      Failure to use the <literal>-package-name</literal> option
+      use the <literal>-this-package-key</literal> option (<xref linkend="using-packages"/>).
+      Failure to use the <literal>-this-package-key</literal> option
       when compiling a package will probably result in disaster, but
       you will only discover later when you attempt to import modules
       from the package.  At this point GHC will complain that the