dart:web_gl: getAttributeLocation returns -1

Question

A call to getAttributeLocation(program,"aTextureCoords") in my code returns -1

However:

• The attribute is active (ie not a duplicate question to Webgl's getAttribLocation oddly returns -1)

• It is spelt correctly

• It has no invalid characters

• It doesn't start with a reserved prefix

• It is shorter than 255 chars

• The passed program isn't invalidated

What could be wrong?

My (embedded) shader code:

<script type="x-shader/x-vertex" id="vertex">
    attribute vec3 aVertexPosition;
    attribute vec2 aTextureCoords;

    uniform mat4 uMVMatrix;
    uniform mat4 uPMatrix;

    varying highp vec2 vTextureCoords;

    void main() {
        gl_Position = uPMatrix*uMVMatrix*vec4(aVertexPosition,1.0);
        vTextureCoords = aTextureCoords;
    }
</script>
<script type="x-shader/x-fragment" id="fragment">
    varying highp vec2 vTextureCoords;

    uniform sampler2D uSampler;

    void main() {
        gl_FragColor = vec4(1.0,0.0,0.0,1.0);
        texture2D(uSampler,vec2(vTextureCoords.s,vTextureCoords.t));
    }
</script>

I don't think the rest of my code is relevant, but I will post it if needed.

---

EDIT:

glGetAttribLocation returns -1 when retrieving existing shader attribute Suggests that binding a location is better than getting a location. I'll try this.

EDIT2: This has fixed my problem, but I would still like to know what caused it in the first place.