[PATCH] D55245: [clang-tidy] Add the abseil-duration-subtraction check

[Roman Lebedev via Phabricator via cfe-commits]

lebedev.ri added inline comments.


================
Comment at: clang-tidy/abseil/DurationRewriter.cpp:35
+getInverseForScale(DurationScale Scale) {
+  static const std::unordered_map<DurationScale,
+                                  std::pair<llvm::StringRef, llvm::StringRef>>
----------------
hwright wrote:
> lebedev.ri wrote:
> > https://llvm.org/docs/ProgrammersManual.html#other-map-like-container-options
> > > We never use hash_set and unordered_set because they are generally very expensive (each insertion requires a malloc) and very non-portable.
> > 
> > Since the key is an enum, [[ https://llvm.org/docs/ProgrammersManual.html#llvm-adt-indexedmap-h | `llvm/ADT/IndexedMap.h` ]] should be a much better fit.
> It doesn't look like `IndexedMap` has a constructor which takes an initializer list.  Without it, this code get a bit more difficult to read, and I'd prefer to optimize for readability here.
The manual still 'recommends' not to use them.
Simple solution: immediately invoked lambda
Better solution: try to add such constructor to `IndexedMap`.


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Comment at: clang-tidy/abseil/DurationRewriter.cpp:68
+      getInverseForScale(Scale);
+  if (const Expr *MaybeCallArg = selectFirst<const Expr>(
+          "e", match(callExpr(callee(functionDecl(
----------------
hwright wrote:
> lebedev.ri wrote:
> > lebedev.ri wrote:
> > > `if (const auto *MaybeCallArg`
> > Early return?
> I'm not quite sure what you mean by `Early return?`  Are you suggesting that the call to `selectFirst` should be pulled out of the `if` conditional, and then the inverse checked to return `llvm::None` first? 
Ah, nevermind then.


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Comment at: clang-tidy/abseil/DurationRewriter.cpp:74
+                     Node, *Result.Context))) {
+    return tooling::fixit::getText(*MaybeCallArg, *Result.Context).str();
+  }
----------------
hwright wrote:
> lebedev.ri wrote:
> > So you generate fix-it, and then immediately degrade it into a string. Weird.
> This doesn't generate a fix-it, it just fetches the text of the given node as a `StringRef` but we're returning a `string`, so we need to convert.
> 
> Is there a more canonical method I should use to fetch a node's text?
I don't know the answer, but have you tried looking what `tooling::fixit::getText()` does internally?


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Comment at: clang-tidy/abseil/DurationRewriter.cpp:156
+llvm::Optional<DurationScale> getScaleForInverse(llvm::StringRef Name) {
+  static const llvm::DenseMap<llvm::StringRef, DurationScale> ScaleMap(
+      {{"ToDoubleHours", DurationScale::Hours},
----------------
Are you very sure this shouldn't be [[ https://llvm.org/docs/ProgrammersManual.html#llvm-adt-stringmap-h | `StringMap` ]]?


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  https://reviews.llvm.org/D55245/new/

https://reviews.llvm.org/D55245