piglit/tests/glslparsertest/shaders/CorrectFull.frag:

    while(bool b = (test_float1 > test_float2)) 

gets Error: scalar/boolean expression expected for 'while'

Changing it to:

    bool b;
    while(b = (test_float1 > test_float2)) 

gets the case pass.

But GLSL spec (both 1.10 and 1.50) section 6.3 says: "Both the condition-expression and the init-expression can declare and initialize a variable", so the case should be allowed.