(This is follow-up of bug#25771 and I'm now filing it as mesa bug)
GLSL spec 1.10 says "There are no implicit conversions between types", no exception.
(While spec starting from 1.20 allows the implicit conversion from "int" to "float" as an exception)
But piglit/tests/glslparsertest/shaders/dataType5.frag (testing against v110) passes with the current mesa:
float f = 1; // int cannot be converted to float, use constructor to do the
ConstantConversions.frag and dataType13.frag also fail with the similar issue.
Fixed with glsl2 merge.
verified with mesa master d442a01ac14382d83cdaac87d2832315ceb3e963.