"Does the speed of light depend on the speed of its source? Before formulating his theory of special relativity, Albert Einstein spent a few years trying to formulate a theory in which the speed of light depends on its source, just like all material projectiles. Likewise, Walter Ritz outlined such a theory, where none of the peculiar effects of Einstein's relativity would hold. By 1913 most physicists abandoned such efforts, accepting the postulate of the constancy of the speed of light. Yet five decades later all the evidence that had been said to prove that the speed of light is independent of its source had been found to be defective."
http://www.martinezwritings..com/m/Relativity.html
This is a euphemism. Actually any relevant and correctly interpreted experiment, e.g. the Michelson-Morley experiment or measurements of the Doppler effect, REFUTES the assumption that the speed of light is independent of the speed of the source. Yet in the post-truth ("post-sanity" is even better) world of science the old principle of Ignatius of Loyola is universally obeyed:
Ignatius of Loyola: "That we may be altogether of the same mind and in conformity with the Church herself, if she shall have defined anything to be black which appears to our eyes to be white, we ought in like manner to pronounce it to be black."
Pentcho Valev