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+// file : libbuild2/action.hxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2019 Code Synthesis Ltd
+// license : MIT; see accompanying LICENSE file
+
+#ifndef LIBBUILD2_ACTION_HXX
+#define LIBBUILD2_ACTION_HXX
+
+#include <libbuild2/types.hxx>
+#include <libbuild2/utility.hxx>
+
+#include <libbuild2/export.hxx>
+
+namespace build2
+{
+ // While we are using uint8_t for the meta/operation ids, we assume
+ // that each is limited to 4 bits (max 128 entries) so that we can
+ // store the combined action id in uint8_t as well. This makes our
+ // life easier when it comes to defining switch labels for action
+ // ids (no need to mess with endian-ness).
+ //
+ // Note that 0 is not a valid meta/operation/action id.
+ //
+ using meta_operation_id = uint8_t;
+ using operation_id = uint8_t;
+ using action_id = uint8_t;
+
+ // Meta-operations and operations are not the end of the story. We also have
+ // operation nesting (currently only one level deep) which is used to
+ // implement pre/post operations (currently, but may be useful for other
+ // things). Here is the idea: the test operation needs to make sure that the
+ // targets that it needs to test are up-to-date. So it runs update as its
+ // pre-operation. It is almost like an ordinary update except that it has
+ // test as its outer operation (the meta-operations are always the same).
+ // This way a rule can recognize that this is "update for test" and do
+ // something differently. For example, if an executable is not a test, then
+ // there is no use updating it. At the same time, most rules will ignore the
+ // fact that this is a nested update and for them it is "update as usual".
+ //
+ // This inner/outer operation support is implemented by maintaining two
+ // independent "target states" (see target::state; initially we tried to do
+ // it via rule/recipe override but that didn't end up well, to put it
+ // mildly). While the outer operation normally "directs" the inner, inner
+ // rules can still be matched/executed directly, without outer's involvement
+ // (e.g., because of other inner rules). A typical implementation of an
+ // outer rule either returns noop or delegates to the inner rule. In
+ // particular, it should not replace or override the inner's logic.
+ //
+ // While most of the relevant target state is duplicated, certain things are
+ // shared among the inner/outer rules, such as the target data pad and the
+ // group state. In particular, it is assumed the group state is always
+ // determined by the inner rule (see resolve_members()).
+ //
+ // Normally, an outer rule will be responsible for any additional, outer
+ // operation-specific work. Sometimes, however, the inner rule needs to
+ // customize its behavior. In this case the outer and inner rules must
+ // communicate this explicitly (normally via the target's data pad) and
+ // there is a number of restrictions to this approach. See
+ // cc::{link,install}_rule for details.
+ //
+ struct action
+ {
+ action (): inner_id (0), outer_id (0) {} // Invalid action.
+
+ // If this is not a nested operation, then outer should be 0.
+ //
+ action (meta_operation_id m, operation_id inner, operation_id outer = 0)
+ : inner_id ((m << 4) | inner),
+ outer_id (outer == 0 ? 0 : (m << 4) | outer) {}
+
+ meta_operation_id
+ meta_operation () const {return inner_id >> 4;}
+
+ operation_id
+ operation () const {return inner_id & 0xF;}
+
+ operation_id
+ outer_operation () const {return outer_id & 0xF;}
+
+ bool inner () const {return outer_id == 0;}
+ bool outer () const {return outer_id != 0;}
+
+ action
+ inner_action () const
+ {
+ return action (meta_operation (), operation ());
+ }
+
+ // Implicit conversion operator to action_id for the switch() statement,
+ // etc. Most places only care about the inner operation.
+ //
+ operator action_id () const {return inner_id;}
+
+ action_id inner_id;
+ action_id outer_id;
+ };
+
+ inline bool
+ operator== (action x, action y)
+ {
+ return x.inner_id == y.inner_id && x.outer_id == y.outer_id;
+ }
+
+ inline bool
+ operator!= (action x, action y) {return !(x == y);}
+
+ bool operator> (action, action) = delete;
+ bool operator< (action, action) = delete;
+ bool operator>= (action, action) = delete;
+ bool operator<= (action, action) = delete;
+
+ LIBBUILD2_SYMEXPORT ostream&
+ operator<< (ostream&, action); // operation.cxx
+
+ // Inner/outer operation state container.
+ //
+ template <typename T>
+ struct action_state
+ {
+ T data[2]; // [0] -- inner, [1] -- outer.
+
+ T& operator[] (action a) {return data[a.inner () ? 0 : 1];}
+ const T& operator[] (action a) const {return data[a.inner () ? 0 : 1];}
+ };
+
+ // Id constants for build-in and pre-defined meta/operations.
+ //
+ const meta_operation_id noop_id = 1; // nomop?
+ const meta_operation_id perform_id = 2;
+ const meta_operation_id configure_id = 3;
+ const meta_operation_id disfigure_id = 4;
+ const meta_operation_id create_id = 5;
+ const meta_operation_id dist_id = 6;
+ const meta_operation_id info_id = 7;
+
+ // The default operation is a special marker that can be used to indicate
+ // that no operation was explicitly specified by the user. If adding
+ // something here remember to update the man page.
+ //
+ const operation_id default_id = 1; // Shall be first.
+ const operation_id update_id = 2; // Shall be second.
+ const operation_id clean_id = 3;
+
+ const operation_id test_id = 4;
+ const operation_id update_for_test_id = 5; // update(for test) alias.
+
+ const operation_id install_id = 6;
+ const operation_id uninstall_id = 7;
+ const operation_id update_for_install_id = 8; // update(for install) alias.
+
+ const action_id perform_update_id = (perform_id << 4) | update_id;
+ const action_id perform_clean_id = (perform_id << 4) | clean_id;
+ const action_id perform_test_id = (perform_id << 4) | test_id;
+ const action_id perform_install_id = (perform_id << 4) | install_id;
+ const action_id perform_uninstall_id = (perform_id << 4) | uninstall_id;
+
+ const action_id configure_update_id = (configure_id << 4) | update_id;
+
+ // Recipe execution mode.
+ //
+ // When a target is a prerequisite of another target, its recipe can be
+ // executed before the dependent's recipe (the normal case) or after.
+ // We will call these "front" and "back" execution modes, respectively
+ // (think "the prerequisite is 'front-running' the dependent").
+ //
+ // There could also be several dependent targets and the prerequisite's
+ // recipe can be execute as part of the first dependent (the normal
+ // case) or last (or for all/some of them; see the recipe execution
+ // protocol in <target>). We will call these "first" and "last"
+ // execution modes, respectively.
+ //
+ // Now you may be having a hard time imagining where a mode other than
+ // the normal one (first/front) could be useful. An the answer is,
+ // compensating or inverse operations such as clean, uninstall, etc.
+ // If we use the last/back mode for, say, clean, then we will remove
+ // targets in the order inverse to the way they were updated. While
+ // this sounds like an elegant idea, are there any practical benefits
+ // of doing it this way? As it turns out there is (at least) one: when
+ // we are removing a directory (see fsdir{}), we want to do it after
+ // all the targets that depend on it (such as files, sub-directories)
+ // were removed. If we do it before, then the directory won't be empty
+ // yet.
+ //
+ // It appears that this execution mode is dictated by the essence of
+ // the operation. Constructive operations (those that "do") seem to
+ // naturally use the first/front mode. That is, we need to "do" the
+ // prerequisite first before we can "do" the dependent. While the
+ // destructive ones (those that "undo") seem to need last/back. That
+ // is, we need to "undo" all the dependents before we can "undo" the
+ // prerequisite (say, we need to remove all the files before we can
+ // remove their directory).
+ //
+ // If you noticed the parallel with the way C++ construction and
+ // destruction works for base/derived object then you earned a gold
+ // star!
+ //
+ // Note that the front/back mode is realized in the dependen's recipe
+ // (which is another indication that it is a property of the operation).
+ //
+ enum class execution_mode {first, last};
+}
+
+#endif // LIBBUILD2_ACTION_HXX