Previously, our incremental build system kept track of the changes between
the current compilation and the previous one, and used its knowledge of
inter-file dependencies to evaluate the impact of each change and emit the
right set of output files.
However, a problem arose if the compiler was not able to extract a
dependency graph successfully. This typically happens if the input program
contains errors. In this case the Angular analysis part of compilation is
never executed.
If a file changed in one of these failed builds, in the next build it
appears unchanged. This means that the compiler "forgets" to emit it!
To fix this problem, the compiler needs to know the set of changes made
_since the last successful build_, not simply since the last invocation.
This commit changes the incremental state system to much more explicitly
pass information from the previous to the next compilation, and in the
process to keep track of changes across multiple failed builds, until the
program can be analyzed successfully and the results of those changes
incorporated into the emit plan.
Fixes#32214
PR Close#33971
Previously, the ngtsc compiler attempted to reuse analysis work from the
previous program during an incremental build. To do this, it had to prove
that the work was safe to reuse - that no changes made to the new program
would invalidate the previous analysis.
The implementation of this had a significant design flaw: if the previous
program had errors, the previous analysis would be missing significant
information, and the dependency graph extracted from it would not be
sufficient to determine which files should be re-analyzed to fill in the
gaps. This often meant that the build output after an error was resolved
would be wholly incorrect.
This commit switches ngtsc to take a simpler approach to incremental
rebuilds. Instead of attempting to reuse prior analysis work, the entire
program is re-analyzed with each compilation. This is actually not as
expensive as one might imagine - analysis is a fairly small part of overall
compilation time.
Based on the dependency graph extracted during this analysis, the compiler
then can make accurate decisions on whether to emit specific files. A new
suite of tests is added to validate behavior in the presence of source code
level errors.
This new approach is dramatically simpler than the previous algorithm, and
should always produce correct results for a semantically correct program.s
Fixes#32388Fixes#32214
PR Close#33862
Alex Rickabaugh