Missing bridge cast causes error in preprocessed source but not in real source

Question

To compile a source file, clang preprocesses it at first and then compiles it. So if I run clang -E, I should get a preprocessed file, that can be compiled with clang -c. But the following code doesn't compile after preprocessing it.

int main(int argc, char * argv[])
{
    NSString* foo = @"bar";

    CFStringRef urlString = CFURLCreateStringByAddingPercentEscapes(
        NULL,
        (CFStringRef)foo,
        NULL,
        (CFStringRef)@"",
        kCFStringEncodingUTF8 );

    CFRelease(urlString);

    return 0;
}

It compiles with clang -c ignoring that foo is cast to CFStringRef without __bridge. When the code is preprocessed, it doesn't compile anymore and clang complains about missing __bridge cast. Is there a flag to disable this behavior or a method to work around this?

Full clang command (used it for compiling and preprocessing with -E)

clang -x objective-c -arch armv7s -fmessage-length=0 -fdiagnostics-show-note-include-stack -fmacro-backtrace-limit=0 -std=gnu99 -fobjc-arc -Wno-trigraphs -fpascal-strings -Os -Wno-missing-field-initializers -Wno-missing-prototypes -Werror=return-type -Wno-implicit-atomic-properties -Werror=deprecated-objc-isa-usage -Werror=objc-root-class -Wno-receiver-is-weak -Wno-arc-repeated-use-of-weak -Wduplicate-method-match -Wno-missing-braces -Wparentheses -Wswitch -Wunused-function -Wno-unused-label -Wno-unused-parameter -Wunused-variable -Wunused-value -Wempty-body -Wuninitialized -Wno-unknown-pragmas -Wno-shadow -Wno-four-char-constants -Wno-conversion -Wconstant-conversion -Wint-conversion -Wbool-conversion -Wenum-conversion -Wshorten-64-to-32 -Wpointer-sign -Wno-newline-eof -Wno-selector -Wno-strict-selector-match -Wundeclared-selector -Wno-deprecated-implementations -DNS_BLOCK_ASSERTIONS=1 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS7.0.sdk -fstrict-aliasing -Wprotocol -Wdeprecated-declarations -g -fvisibility=hidden -Wno-sign-conversion -miphoneos-version-min=7.0 -c main.m

Show us the rest of the flags you’re passing to clang. My guess is that in one case you’ve enabled ARC and in the other case you haven’t. — al45tair, Jan 15 '14 at 16:35
Adding __bridge is not an option for me, because I am doing some transformations to the preprocessed source — Elviss Strazdins, Jan 15 '14 at 16:50
@ElvissStrazdiņš: `clang -E main.m > main.i ; clang -x objective-c -c main.i` does not give any warnings with my Xcode 5.2. — Martin R, Jan 15 '14 at 18:30
@MartinR: you should enable ARC to see the error, add `-fobjc-arc` argument. — Mārtiņš Možeiko, Jan 15 '14 at 18:56

score 4 · Accepted Answer · edited May 23 '17 at 12:21

4

Compare ARC - implicit bridging: "CFString.h" and other Core Foundation headers contain the macros

CF_IMPLICIT_BRIDGING_ENABLED
...
CF_IMPLICIT_BRIDGING_DISABLED

which are expanded to

_Pragma("clang arc_cf_code_audited begin")
...
_Pragma("clang arc_cf_code_audited end")

and that causes Clang to not complain about missing __bridge casts.

The pragmas are "consumed" by the preprocessor and therefore not in the preprocessed file. Since you are transforming the preprocessed source anyway, you can add these pragmas to the start/end of the preprocessed file again. Then there will be no warnings when compiling it.

edited May 23 '17 at 12:21

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answered Jan 15 '14 at 19:10

Martin R

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Thank you, that helped me a lot! I also tested other pragmas, they are all left after preprocessing, why is this consumed? Do you know, is it possible to disable this behavior? – Elviss Strazdins Jan 15 '14 at 23:10
@ElvissStrazdiņš: I have no idea. – Martin R Jan 16 '14 at 05:20

Missing bridge cast causes error in preprocessed source but not in real source

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