I think since previously we did not send the icon in the proto and now we will send it always when a StreamlitPage is provided, it would be good to add some test coverage to the frontend tests that verify the beahviour when an empty string is provided for the icon (this seems to be the default in StreamlitPage).

Pending behaviour change approval from @jrieke

I think since previously we did not send the icon in the proto and now we will send it always when a StreamlitPage is provided, it would be good to add some test coverage to the frontend tests that verify the beahviour when an empty string is provided for the icon (this seems to be the default in StreamlitPage).

Sure, I'll add more tests. But before, I wonder why self._icon isn't reassigned during the StreamlitPage initialization while it is in page_link. Do you have an idea ?

I think since previously we did not send the icon in the proto and now we will send it always when a StreamlitPage is provided, it would be good to add some test coverage to the frontend tests that verify the beahviour when an empty string is provided for the icon (this seems to be the default in StreamlitPage).

Sure, I'll add more tests. But before, I wonder why self._icon isn't reassigned during the StreamlitPage initialization while it is in page_link. Do you have an idea ?

streamlit/lib/streamlit/navigation/page.py

Lines 229 to 230 in 1585ce4

	if self._icon:
	validate_icon_or_emoji(self._icon)

streamlit/lib/streamlit/elements/widgets/button.py

Lines 920 to 921 in 1585ce4

	if icon is not None:
	page_link_proto.icon = validate_icon_or_emoji(icon)

In button.py it is being added to the proto message that will be sent to the streamlit FE.

I think since previously we did not send the icon in the proto and now we will send it always when a StreamlitPage is provided, it would be good to add some test coverage to the frontend tests that verify the beahviour when an empty string is provided for the icon (this seems to be the default in StreamlitPage).

Sure, I'll add more tests. But before, I wonder why self._icon isn't reassigned during the StreamlitPage initialization while it is in page_link. Do you have an idea ?

streamlit/lib/streamlit/navigation/page.py

Lines 229 to 230 in 1585ce4

	if self._icon:
	validate_icon_or_emoji(self._icon)

streamlit/lib/streamlit/elements/widgets/button.py

Lines 920 to 921 in 1585ce4

	if icon is not None:
	page_link_proto.icon = validate_icon_or_emoji(icon)

In button.py it is being added to the proto message that will be sent to the streamlit FE.

I'm saying that because it feels a bit counter intuitive to me (both in terms of consistency and the fact that validate_icon_or_emoji is supposed to return a string). That being said, currently in develop using the code below, the first st.page_link works fine while the second one triggers a StreamlitAPIException: The value "" is not a valid emoji.

page = st.Page(
    "a_page_path_stem.py",
    title="A title",
    icon="",
)

st.page_link(page) # works fine
st.page_link(page, icon="")  # triggers an error

By the way, I added a few more tests but the last one is failing because of this behaviour..

I think since previously we did not send the icon in the proto and now we will send it always when a StreamlitPage is provided, it would be good to add some test coverage to the frontend tests that verify the beahviour when an empty string is provided for the icon (this seems to be the default in StreamlitPage).

Sure, I'll add more tests. But before, I wonder why self._icon isn't reassigned during the StreamlitPage initialization while it is in page_link. Do you have an idea ?

streamlit/lib/streamlit/navigation/page.py

Lines 229 to 230 in 1585ce4

	if self._icon:
	validate_icon_or_emoji(self._icon)

streamlit/lib/streamlit/elements/widgets/button.py

Lines 920 to 921 in 1585ce4

	if icon is not None:
	page_link_proto.icon = validate_icon_or_emoji(icon)

In button.py it is being added to the proto message that will be sent to the streamlit FE.

I'm saying that because it feels a bit counter intuitive to me (both in terms of consistency and the fact that validate_icon_or_emoji is supposed to return a string). That being said, currently in develop using the code below, the first st.page_link works fine while the second one triggers a StreamlitAPIException: The value "" is not a valid emoji.

page = st.Page(
    "a_page_path_stem.py",
    title="A title",
    icon="",
)

st.page_link(page) # works fine
st.page_link(page, icon="")  # triggers an error

By the way, I added a few more tests but the last one is failing because of this behaviour..

I don't follow your concern about consistency. You must assign the value to the proto message in button.py because that is how the server communicates with the frontend. Maybe you can give an example of what you want to do differently to demonstrate your concern?

An empty string is not a valid emoji, so this error seems correct to me. We want to let people know that they haven't provided an actual icon at the API level so that they can correct their code. Internally, whether we send an empty string for this property or leave it out of the proto message is an implementation detail and as long as it is handled correctly E2E either way should be fine.

I think since previously we did not send the icon in the proto and now we will send it always when a StreamlitPage is provided, it would be good to add some test coverage to the frontend tests that verify the beahviour when an empty string is provided for the icon (this seems to be the default in StreamlitPage).

Sure, I'll add more tests. But before, I wonder why self._icon isn't reassigned during the StreamlitPage initialization while it is in page_link. Do you have an idea ?

streamlit/lib/streamlit/navigation/page.py

Lines 229 to 230 in 1585ce4

	if self._icon:
	validate_icon_or_emoji(self._icon)

streamlit/lib/streamlit/elements/widgets/button.py

Lines 920 to 921 in 1585ce4

	if icon is not None:
	page_link_proto.icon = validate_icon_or_emoji(icon)

In button.py it is being added to the proto message that will be sent to the streamlit FE.

I'm saying that because it feels a bit counter intuitive to me (both in terms of consistency and the fact that validate_icon_or_emoji is supposed to return a string). That being said, currently in develop using the code below, the first st.page_link works fine while the second one triggers a StreamlitAPIException: The value "" is not a valid emoji.

page = st.Page(
    "a_page_path_stem.py",
    title="A title",
    icon="",
)

st.page_link(page) # works fine
st.page_link(page, icon="")  # triggers an error

By the way, I added a few more tests but the last one is failing because of this behaviour..

I don't follow your concern about consistency. You must assign the value to the proto message in button.py because that is how the server communicates with the frontend. Maybe you can give an example of what you want to do differently to demonstrate your concern?

An empty string is not a valid emoji, so this error seems correct to me. We want to let people know that they haven't provided an actual icon at the API level so that they can correct their code. Internally, whether we send an empty string for this property or leave it out of the proto message is an implementation detail and as long as it is handled correctly E2E either way should be fine.

Thanks for the explanation. Actually, I used the term consistency because I was expecting the error to be triggered in both cases (see below) but I'm overlooking something for sure.

# case 1
page_1 = st.Page(
    "a_page_path_stem.py",
    title="A title",
    icon="", # should? trigger an error
)

# case 2
page_2 = st.Page(
    "a_page_path_stem.py",
    title="A title",
    icon=":material/animation:",
)
st.page_link(page_2, icon="") # triggers an error

Thanks for the explanation. Actually, I used the term consistency because I was expecting the error to be triggered in both cases (see below) but I'm overlooking something for sure.

# case 1
page_1 = st.Page(
    "a_page_path_stem.py",
    title="A title",
    icon="", # should? trigger an error
)

# case 2
page_2 = st.Page(
    "a_page_path_stem.py",
    title="A title",
    icon=":material/animation:",
)
st.page_link(page_2, icon="") # triggers an error

I see, this is a bit different then the example you provided previously, I agree that it would be clearer if st.page and st.page_link both throw an error if icon is an empty string. Before making that change we should also get agreement from @jrieke on the behaviour change for st.page.

Note: I was thinking of React tests to cover a blank string for the icon in the proto. I think currently we don't have tests for that but it seems we do check if icon is truthy and skip rendering if it is not.

Yeah this seems fine to me!

I'm wondering if there are situations where you have an icon on the page but don't want it to show up on the page link. But that seems like such a small niche case that I wouldn't worry about it now and just wait to see if someone complains. In the original issue, it was mentioned that we could allow icon=False for this situation. I think that's an option, but I also don't love that API; so I'd just merge this as is now and worry about that special case later :)

@abokey1 I think the pending items before merging this PR are:

• Potentially make the handling of an empty string consistent between st.page and st.page_link as you suggested. We have agreement from Johannes on this so I think it would be good to add it here.
• React test coverage.

Are you able to look into these items? If not I might be able to find some time to finish this off so we can merge it.

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@abokey1 made some updates to add tests and make the change you suggested to keep the handling of icon="" consistent and merged. Thank-you for contributing 🙌