type-correct

LLVM LibClang / LibTooling solution to 'fix' types, rewriting inconsistent use of types to make them consistent.

Automatic conversions

#include <string.h>

int main(void) {

    /* FROM */
    const int n = strlen("FOO");

    /* TO */
    const size_t n = strlen("FOO");

    /* FROM */
    for(int i=0; i<strlen("BAR"); i++) {}

    /* TO */
    for(size_t i=0; i<strlen("BAR"); i++) {}

    /* FROM */
    int f(long b) { return b; }
    static const int c = f(5);

    /* TO */
    long f(long b) { return b; }
    static const long c = f(5);
}

Justification

Often when building third-party libraries I get a bunch of warnings "comparison between signed and unsigned types is UB".

Not every such occurrence has a trivial solution. But—in my experience—most do. Usually switching just one var from int to size_t also requires tracing all use of that var and changing all those types to size_t also.

From:

unsigned long f() {return 0;}
const size_t v = f();

int main() {
    std::vector<float> vec;
    for(int i=0; i<vec.size(); i++) {}
}

To:

unsigned long f() {return 0;}
const unsigned long v = f();

int main() {
    std::vector<float> vec;
    for(size_t i=0; i<vec.size(); i++) {}
}

PS: I'm aware that size_type isn't necessarily size_t—and that decltype(vec)::size_type would be more correct—but using it here anyway. Just to reiterate: C++ is an afterthought, my main target is C.

Integer promotion

#include <limits.h>

short sh=SHRT_MAX;
int i=INT_MAX;
long l=LONG_MAX;
long long ll=LLONG_MAX; /* C99 */

Technically, these are all defined and expected [on clang as an ImplicitCastExpr]:

ll = l;
l = i;
i = sh;

(but the other direction, 'narrowing', is implementation defined)

However, IMHO, people doing int sl = strlen(s); actually want size_t. This opinionated view is the assumption made for type_correct.

But… attempts are made to be reasonably conservative. See type_correct/tests/test_type_correct.cpp for false positive and true positive checks.

Build instructions

Install compiler suite, CMake, and LLVM (from brew, apt, or source), then run:

mkdir build && cd build
cmake .. \
      -DCMAKE_BUILD_TYPE='Debug' \
      -DCT_Clang_INSTALL_DIR='/usr/local/opt/llvm'

(replace /usr/local/opt/llvm with your LLVM install dir)

Thanks

Boilerplate from https://github.com/banach-space/clang-tutor

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