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-rw-r--r--build/target17
1 files changed, 10 insertions, 7 deletions
diff --git a/build/target b/build/target
index f9aa50a..3d395d4 100644
--- a/build/target
+++ b/build/target
@@ -30,13 +30,13 @@ namespace build
// Target state.
//
- enum class target_state {unknown, unchanged, changed, failed};
+ enum class target_state {unknown, postponed, unchanged, changed, failed};
// Recipe.
//
- // The returned target state should be either changed or unchanged.
- // If there is an error, then the recipe should throw rather than
- // returning failed.
+ // The returned target state should be changed, unchanged, or
+ // postponed. If there is an error, then the recipe should throw
+ // rather than returning failed.
//
// The recipe execution protocol is as follows: before executing
// the recipe, the caller sets the target's state to failed. If
@@ -44,10 +44,13 @@ namespace build
// failed, then the caller sets it to the returned value. This
// means that the recipe can set the target's state manually to
// some other value. For example, setting it to unknown will
- // result in the recipe to be executed again if this target is
- // a prerequisite of another target. Note that in this case the
+ // result in the recipe to be executed again if this target is a
+ // prerequisite of another target. Note that in this case the
// returned by the recipe value is still used (by the caller) as
// the resulting target state for this execution of the recipe.
+ // Returning postponed from the last call to the recipe means
+ // that the action could not be executed at this time (see fsdir
+ // clean for an example).
//
using recipe_function = target_state (action, target&);
using recipe = std::function<recipe_function>;
@@ -107,7 +110,7 @@ namespace build
// action. It is incremented during the match phase and then decremented
// during execution, before running the recipe. As a result, the recipe
// can detect the last chance (i.e., last dependent) to execute the
- // command ("front-running" vs "back-running" recipes).
+ // command (see alsoe first/last execution modes in <operation>).
//
// Note that setting a new recipe (which happens when we match the rule
// and which in turn is triggered by the first dependent) clears this