[all-commits] [llvm/llvm-project] 808632: [-Wunsafe-buffer-usage] NFC: Implement fix-strateg...

[NoQ via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 8086323a91b597e9510d15f14d56d358221ff539
      https://github.com/llvm/llvm-project/commit/8086323a91b597e9510d15f14d56d358221ff539
  Author: Artem Dergachev <adergachev at apple.com>
  Date:   2022-12-16 (Fri, 16 Dec 2022)

  Changed paths:
    M clang/include/clang/Analysis/Analyses/UnsafeBufferUsage.h
    M clang/include/clang/Basic/DiagnosticGroups.td
    M clang/include/clang/Basic/DiagnosticSemaKinds.td
    M clang/lib/Analysis/UnsafeBufferUsage.cpp
    M clang/lib/Sema/AnalysisBasedWarnings.cpp

  Log Message:
  -----------
  [-Wunsafe-buffer-usage] NFC: Implement fix-strategies and variable-use-claiming.

This patch adds more abstractions that we'll need later for emitting
-Wunsafe-buffer-usage fixits. It doesn't emit any actual fixits,
so no change is observed behavior, but it introduces a way to emit fixits,
and existing tests now verify that the compiler still emits no fixits,
despite knowing how to do so.

The purpose of our code transformation analysis is to fix variable types
in the code from raw pointer types to C++ standard collection/view types.

The analysis has to decide on its own which specific type is
the most appropriate for every variable. This patch introduces
the Strategy class that maps variables to their most appropriate types.

In D137348 we've introduced the Gadget abstraction, which describes
a rigid AST pattern that the analysis "fully understands" and may need
to fix. Which specific fix is actually necessary for a given Gadget,
and whether it's necessary at all, and whether it's possible in the first place,
depends on the Strategy. So, this patch adds a virtual method which every
gadget can implement in order to teach the analysis how to fix that gadget:

  Gadget->getFixits(Strategy)

However, even if the analysis knows how to fix every Gadget, doesn't
necessarily mean it can fix the variable. Some uses of the variable may have
never been covered by Gadgets, which corresponds to the situation that
the analysis doesn't fully understand how the variable is used. This patch
introduces a Tracker class that tracks all variable uses (i.e. DeclRefExprs)
in the function. Additionally, each Gadget now provides a new virtual method

  Gadget->getClaimedVarUseSites()

that the Tracker can call to see which DeclRefExprs are "claimed" by the Gadget.
In order to fix the variable with a certain Strategy, the Tracker needs to
confirm that there are no unclaimed uses, and every Gadget has to provide
a fix for that Strategy.

This "conservative" behavior guarantees that fixes emitted by our analysis
are correct by construction. We can now be sure that the analysis won't
attempt to emit a fix if it doesn't understand the code. Later, as we implement
more getFixits() methods in individual Gadget classes, we'll start
progressively emitting more and more fixits.

Differential Revision: https://reviews.llvm.org/D138253