[CI] Check that a second build has nothing to do - #23056
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Test Results 23 files 23 suites 5d 6h 25m 3s ⏱️ For more details on these failures, see this check. Results for commit b2b7f9d. ♻️ This comment has been updated with latest results. |
Building an already built tree twice in a row must be a no-op, apart from etc/gitinfo.txt which the gitinfotxt target rewrites on every build by design. When that is not the case, every incremental build pays for the targets that are needlessly redone plus everything depending on them. Add a null build check that runs on all platforms right after the build: it fingerprints every file in the build tree, builds again, and reports what was written. Doing it this way rather than parsing build tool output keeps it working across Ninja, Makefiles and MSBuild alike. The verdict is only acted on at the very end, after ctest, so that a spurious rebuild does not cost us the test results. 🤖 Done with the help of AI
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ROOT_STANDARD_LIBRARY_PACKAGE(... NO_SOURCES) provided the dummy source file that add_library() needs as the output of a custom command that touches it. All the packages of one directory share that output, and listing one custom command output in several independent targets that build in parallel is not supported; core/clingutils alone has 15 of them. Ninja and Make happen to get away with it, but with MSBuild the touch runs again on every build, so 14 of the 15 STL dictionaries were recompiled and relinked every time, along with everything depending on them. Write the file at configure time instead. Nothing touches it at build time anymore, so it cannot go stale under the targets that compile it. 🤖 Done with the help of AI
MSBuild re-executes these post-build events even when the build has nothing to do, and `cmake -E copy` rewrites its destination unconditionally, so every null build modified those files. Ninja and Makefiles are immune because there POST_BUILD steps only run when the target itself relinks. Use `cmake -E copy_if_different` so a no-op event leaves the destination untouched, and replace the data.h POST_BUILD hack with configure_file(... COPYONLY), the convention the sibling test directories already use for such runtime inputs. 🤖 Done with the help of AI
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Building an already built tree twice in a row must be a no-op, apart from etc/gitinfo.txt which the gitinfotxt target rewrites on every build by design. When that is not the case, every incremental build pays for the targets that are needlessly redone plus everything depending on them.
Add a null build check that runs on all platforms right after the build: it fingerprints every file in the build tree, builds again, and reports what was written. Doing it this way rather than parsing build tool output keeps it working across Ninja, Makefiles and MSBuild alike.
The verdict is only acted on at the very end, after ctest, so that a spurious rebuild does not cost us the test results.
🤖 Done with the help of AI