Fix #7011: check possibly side-effecting transform #7016
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The transform function in question can be overridden with a version that produces side effects. If that is the case, and if the superclass transform function is called from the overridden transform function, the overridden transform function might be executed twice with all its side effects. This commit makes sure the transform function is not called twice on the same input. An example where it can go wrong is: https://github.com/lampepfl/dotty/blob/9a4b7d39a595dba3c0baf340b0bf911844fcae69/compiler/src/dotty/tools/dotc/typer/Typer.scala#L1080 Here, the transform function performs the side effect of entering a symbol into scope. Furthermore, if the symbol already exists in scope, it emits an error. Hence, if we call this function twice on the same argument, we are guaranteed to get an error.
anatoliykmetyuk
changed the title
anatoliykmetyuk
changed the title
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@anatoliykmetyuk could you try to refactor the the code to make the diff smaller. |
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Basically if-else got replaced by the new context val at the beginning. What was inside the else block stayed the same. |
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It is also to have a clean line history |
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If-else is gone now, hence indentation changed, hence the large diff |
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I don't think we can do anything about it |
nicolasstucki
approved these changes
Aug 10, 2019
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The transform function in question can be overridden with a version
that produces side effects. If that is the case, and if the superclass
transform function is called from the overridden transform function,
the overridden transform function might be executed twice with all its
side effects. This commit makes sure the transform function is not
called twice on the same input. An example where it can go wrong is:
https://github.com/lampepfl/dotty/blob/9a4b7d39a595dba3c0baf340b0bf911844fcae69/compiler/src/dotty/tools/dotc/typer/Typer.scala#L1080-L1094
Here, the transform function performs the side effect of entering a symbol
into scope. Furthermore, if the symbol already exists in scope, it emits
an error. Hence, if we call this function twice on the same argument,
we are guaranteed to get an error.