[cfe-dev] clang ast: how do I find out whether a catch is done by const reference

[Aaron Ballman]

On Thu, Jul 16, 2015 at 5:05 PM, Tobias Langner
<randomcppprogrammer at gmail.com> wrote:
>
> On 16 Jul 2015, at 22:50, Aaron Ballman <aaron at aaronballman.com> wrote:
>
> On Thu, Jul 16, 2015 at 4:41 PM, Tobias Langner
> <randomcppprogrammer at gmail.com> wrote:
>
> Hi,
>
> I want to write a check that tests whether a catch is done by const
> reference or not. I currently have the following code but it can’t
> distinguish between const reference and reference:
>
>  const auto *catchStmt = Result.Nodes.getNodeAs<CXXCatchStmt>("catch");
>  if (catchStmt != nullptr) {
>    auto caughtType = catchStmt->getCaughtType();
>
>
> This returns the QualType you are looking for.
>
> caughType.isConstant() && caughtType->isLValueReferenceType();
>
> should tell you if it's a const-qualified lvalue reference type.
>
> ~Aaron
>
> This gives me the same result as using QualType::isConstQualified() (see
> below). Both my examples are detected as not being caught by const
> reference:
>
> void catchByReference() {
>   try {
>     testThrowFunc();
>   } catch (logic_error &e) {
>   }
> }
>
> void catchByConstReference() {
>   try {
>     testThrowFunc();
>   } catch (const logic_error &e) {
>   }
> }
>
> giving this result:
>
> /Users/tobias/Documents/Development/git/llvm/build/ninja-debug/../../llvm/tools/clang/tools/extra/test/clang-tidy/misc-throw-by-value-catch-by-reference.cpp:44:12:
> warning: catch by const reference to avoid unnecessary copies
> [misc-throw-by-value-catch-by-reference]
>   } catch (logic_error &e) {
>            ^
> /Users/tobias/Documents/Development/git/llvm/build/ninja-debug/../../llvm/tools/clang/tools/extra/test/clang-tidy/misc-throw-by-value-catch-by-reference.cpp:51:12:
> warning: catch by const reference to avoid unnecessary copies
> [misc-throw-by-value-catch-by-reference]
>   } catch (const logic_error &e) {
>
> so for both caughtTypes of these catch statements, neither isConstant() nor
> isConstQualified() returns true.

Do you get the same results if you look at the canonical type instead?

auto QT = caughtType->getCaughtType().getCanonicalType();
if (QT.isConstQualified() && QT->isLValueReferenceType()) ...

~Aaron

>
> Regards
> Tobias
>
>    auto *type = caughtType.getTypePtr();
>    auto *varDecl = catchStmt->getExceptionDecl();
>    if (type->isPointerType()) {
>      diag(varDecl->getLocStart(),
>           "catch by const reference instead of pointer");
>    } else if (!type->isReferenceType()) {
>      diag(varDecl->getLocStart(), "catch by const reference");
>    } else {
>      if (caughtType.isConstQualified() == false) {
>        diag(varDecl->getLocStart(),
>             "catch by const reference to avoid unnecessary copies");
>      }
>    }
>  }
>
> I tried looking at the varDecl but from there I can’t even find out how to
> get the QualType. Can somebody give me a hint?
>
> Regards
> Tobias
> _______________________________________________
> cfe-dev mailing list
> cfe-dev at cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev
>
>