Add update operation-specific variable with unmatch|match additional values

Note that the unmatch (match but do not update) and match (update during
match) values are only supported by certain rules (and potentially only for
certain prerequisite types).

Additionally:

- All operation-specific variables are now checked for false as an override
  for the prerequisite-specific include value. In particular, this can now be
  used to disable a prerequisite for update, for example:

  ./: exe{test}: update = false

- The cc::link_rule now supports the update=match value for headers and ad hoc
  prerequisites. In particular, this can be used to make sure all the library
  headers are updated before matching any of its (or dependent's) object
  files.

1 files changed, 26 insertions, 10 deletions

diff --git a/libbuild2/install/rule.cxx b/libbuild2/install/rule.cxx
index b8d716d..db9c64a 100644
--- a/libbuild2/install/rule.cxx
+++ b/libbuild2/install/rule.cxx
@@ -74,6 +74,8 @@ namespace build2
     {
       tracer trace ("install::alias_rule::apply");
 
+      context& ctx (t.ctx);
+
       // Pass-through to our installable prerequisites.
       //
       // @@ Shouldn't we do match in parallel (here and below)?
@@ -125,7 +127,7 @@ namespace build2
         //
         // Note: not the same as lookup_install() above.
         //
-        auto l ((*pt)["install"]);
+        auto l ((*pt)[ctx.current_ovar]); // "install"
         if (l && cast<path> (l).string () == "false")
         {
           l5 ([&]{trace << "ignoring " << *pt << " (not installable)";});
@@ -207,6 +209,8 @@ namespace build2
     {
       tracer trace ("install::group_rule::apply");
 
+      context& ctx (t.ctx);
+
       // Resolve group members.
       //
       // Remember that we are called twice: first during update for install
@@ -245,7 +249,7 @@ namespace build2
           //
           // Note: not the same as lookup_install() above.
           //
-          auto l ((*mt)["install"]);
+          auto l ((*mt)[ctx.current_ovar]); // "install"
           if (l && cast<path> (l).string () == "false")
           {
             l5 ([&]{trace << "ignoring " << *mt << " (not installable)";});
@@ -290,11 +294,13 @@ namespace build2
     {
       if (p.is_a<exe> ())
       {
-        // Feels like one day this should be unified with include (see
-        // context::var_include).
+        // Note that while include() checks for install=false, here we need to
+        // check for explicit install=true. We could have re-used the lookup
+        // performed by include(), but then we would have had to drag it
+        // through and also diagnose any invalid values.
         //
         if (p.vars.empty () ||
-            cast_empty<path> (p.vars["install"]).string () != "true")
+            cast_empty<path> (p.vars[t.ctx.current_ovar]).string () != "true")
           return nullptr;
       }
 
@@ -314,6 +320,8 @@ namespace build2
     {
       tracer trace ("install::file_rule::apply");
 
+      context& ctx (t.ctx);
+
       // Note that we are called both as the outer part during the update-for-
       // un/install pre-operation and as the inner part during the un/install
       // operation itself.
@@ -381,7 +389,7 @@ namespace build2
         //
         // Note: not the same as lookup_install() above.
         //
-        auto l ((*pt)["install"]);
+        auto l ((*pt)[ctx.current_ovar]); // "install"
         if (l && cast<path> (l).string () == "false")
         {
           l5 ([&]{trace << "ignoring " << *pt << " (not installable)";});
@@ -936,6 +944,8 @@ namespace build2
     target_state file_rule::
     perform_install (action a, const target& xt) const
     {
+      context& ctx (xt.ctx);
+
       const file& t (xt.as<file> ());
       const path& tp (t.path ());
 
@@ -1033,7 +1043,7 @@ namespace build2
       //
       if (!tp.empty ())
       {
-        install_target (t, cast<path> (t["install"]), 1);
+        install_target (t, cast<path> (t[ctx.current_ovar]), 1); // "install"
         r |= target_state::changed;
       }
 
@@ -1160,6 +1170,8 @@ namespace build2
                  const path& name,
                  uint16_t verbosity)
     {
+      context& ctx (rs.ctx);
+
       assert (t != nullptr || !name.empty ());
       path f (chroot_path (rs, base.dir) /
               (name.empty () ? t->path ().leaf () : name));
@@ -1196,7 +1208,7 @@ namespace build2
         if (verb >= verbosity && verb >= 2)
           text << "rm " << relf;
 
-        if (!rs.ctx.dry_run)
+        if (!ctx.dry_run)
         {
           try
           {
@@ -1225,7 +1237,7 @@ namespace build2
         if (verb >= verbosity && verb >= 2)
           print_process (args);
 
-        if (!rs.ctx.dry_run)
+        if (!ctx.dry_run)
           run (pp, args);
       }
 
@@ -1235,6 +1247,8 @@ namespace build2
     target_state file_rule::
     perform_uninstall (action a, const target& xt) const
     {
+      context& ctx (xt.ctx);
+
       const file& t (xt.as<file> ());
       const path& tp (t.path ());
 
@@ -1298,7 +1312,9 @@ namespace build2
       target_state r (target_state::unchanged);
 
       if (!tp.empty ())
-        r |= uninstall_target (t, cast<path> (t["install"]), 1);
+        r |= uninstall_target (t,
+                               cast<path> (t[ctx.current_ovar]), // "install"
+                               1);
 
       // Then installable ad hoc group members, if any. To be anally precise,
       // we would have to do it in reverse, but that's not easy (it's a