Opened 9 years ago

Closed 9 years ago

#4945 closed Bug (fixed)

The new version of LLVM in Xcode 4.4 reports an error in Controller.m

Reported by: smono Owned by: livings124
Priority: Low Milestone: 2.60
Component: Mac Client Version: 2.52
Severity: Trivial Keywords:
Cc:

Description

When compiling with Xcode 4.4 (i.e., Apple LLVM 4.0 which is not under NDA), an error is reported in Controller.m:

macosx/Controller.m:2101:13: Return type 'int' must match previous return type 'NSComparisonResult' (aka 'long') when block literal has unspecified explicit return type

The issue can be resolved with a cast, see attached diff.

Attachments (2)

comparisonresultcast.diff (515 bytes) - added by smono 9 years ago.
explicitreturntype.diff (1.0 KB) - added by smono 9 years ago.
Explicit return type instead of a cast

Download all attachments as: .zip

Change History (8)

Changed 9 years ago by smono

comment:1 Changed 9 years ago by livings124

  • Component changed from Transmission to Mac Client
  • Milestone changed from None Set to 2.60
  • Owner set to livings124
  • Status changed from new to assigned

comment:2 Changed 9 years ago by livings124

  • Priority changed from Normal to Low
  • Severity changed from Normal to Trivial

comment:3 Changed 9 years ago by livings124

NSOrderedSame is in the NSComparisonResult enum. Why would the cast be necessary?

Changed 9 years ago by smono

Explicit return type instead of a cast

comment:4 Changed 9 years ago by smono

That is a good question that you'll have to ask the compiler about.

Without the cast, it throws an error (not a warning) and hence does not complete the build. With the cast it builds.

From the error message one gleans that NSComparisonResult is a long and NSOrderedSame is an int (no idea why) and that discrepancy apparently triggers a compiler check for inconsistent return values in blocks with unspecified return types.

comment:5 Changed 9 years ago by smono

This is of course a trivial issue, but I took the opportunity to dig a little deeper into block declarations.

First, it all begins because the compiler somehow does think that NSOrderedSame has the same type as NSComparisonResult, which I would have expected.

However, once that difference is established, a block with an undeclared return type will have its return type inferred by the compiler (unlike functions).

Since there are two return statements with different types, this is an ambiguity that the new compiler (Apple LLVM 4.0) flags as an error.

So if a cast on the return is a bit ugly, another solution could be to make the return type from the block explicit, as in the attached diff (explicitreturntype.diff). The cast will of course still happen, but in this case it can be handled silently by the compiler in an unambiguous manner.

Again, apart from getting the code to compile, to me this was just a useful opportunity to get a bit deeper into blocks.

comment:6 Changed 9 years ago by livings124

  • Resolution set to fixed
  • Status changed from assigned to closed

Thanks for looking this over! r13354.

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