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-rw-r--r--libbuild2/cc/link-rule.hxx34
1 files changed, 20 insertions, 14 deletions
diff --git a/libbuild2/cc/link-rule.hxx b/libbuild2/cc/link-rule.hxx
index 0fc1790..655d36a 100644
--- a/libbuild2/cc/link-rule.hxx
+++ b/libbuild2/cc/link-rule.hxx
@@ -278,22 +278,28 @@ namespace build2
// have already been executed, then it was for install.
//
// This has an interesting implication: it means that this rule cannot
- // be used to update targets during match. Specifically, we cannot be
- // executed for group resolution purposes (not a problem) nor as part
- // of the generated source update. The latter case can be a problem:
- // imagine a code generator that itself may need to be updated before
- // it can be used to re-generate some out-of-date source code. As an
- // aside, note that even if we were somehow able to communicate the
- // "for install" in this case, the result of such an update may not
- // actually be "usable" (e.g., not runnable because of the missing
+ // be used to update targets to be installed during match (since we
+ // would notice that they are for install too late). Specifically, we
+ // cannot be executed for group resolution purposes (should not be a
+ // problem) nor as part of the generated source update. The latter
+ // case can be a problem: imagine a source code generator that itself
+ // may need to be updated before it can be used to re-generate some
+ // out-of-date source code (or, worse, both the generator and the
+ // target to be installed depend on the same library).
+ //
+ // As an aside, note that even if we were somehow able to communicate
+ // the "for install" in this case, the result of such an update may
+ // not actually be "usable" (e.g., not runnable because of the missing
// rpaths). There is another prominent case where the result may not
- // be usable: cross-compilation.
+ // be usable: cross-compilation (in fact, if you think about it, "for
+ // install" is quite similar to cross-compilation: we are building for
+ // a foreign "environment" and thus cannot execute the results of the
+ // build).
//
- // So the current (admittedly fuzzy) thinking is that a project shall
- // not try to use its own build for update since it may not be usable
- // (because of cross-compilations, being "for install", etc). Instead,
- // it should rely on another, "usable" build of itself (this, BTW, is
- // related to bpkg's build-time vs run-time dependencies).
+ // So the current thinking is that a project shall not try to use its
+ // own "for install" (or, naturally, cross-compilation) build for
+ // update since it may not be usable. Instead, it should rely on
+ // another, "usable" build.
//
optional<bool> for_install;