Shader Compilation Error: #version required and missing. / 'varying' : syntax error: syntax error

[EndlessJour9527]

Critical Error Log:

Shader(18) compilation error:
ERROR: 0:1: '' :  #version required and missing.
ERROR: 0:2: 'varying' : syntax error: syntax error

============== shader source ==============
precision mediump float;
varying vec4 v_color;
void main() {
    gl_FragColor = v_color;
}

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Case Path Example:
https://github.com/M-CreativeLab/WebGL/tree/main/sdk/tests/conformance/attribs/gl-disabled-vertex-attrib.html