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[fab] Let an extended Fab grow to fit a wrapping label #49529

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[fab] Let an extended Fab grow to fit a wrapping label #49529

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[fab] Let an extended Fab grow to fit a wrapping label
teoarjun Oct 22, 2026
b657df3
Merge branch 'master' into fix/fab-extended-wrapping-label
ZeeshanTamboli Oct 26, 2026
c12baa2
[fab] Size the extended Fab to its content, not its parent
teoarjun Oct 27, 2026
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17 changes: 10 additions & 7 deletions packages/mui-material/src/Fab/Fab.js
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Original file line number Diff line number Diff line change
Expand Up @@ -103,31 +103,34 @@ const FabRoot = styled(ButtonBase, {
props: { variant: 'extended' },
style: {
borderRadius: 48 / 2,
padding: '0 16px',
// Vertical padding and a content-sized height rather than a fixed
// height, so a label that wraps stays inside the button. `fit-content`
// rather than `auto` keeps a flex or grid parent from stretching it.
padding: '8px 16px',
width: 'auto',
minHeight: 'auto',
height: 'fit-content',
minWidth: 48,
height: 48,
minHeight: 48,

@ZeeshanTamboli ZeeshanTamboli Oct 26, 2026

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Breaking change: a smaller height customization no longer applies.

On master the extended variant set minHeight: 'auto', so a smaller height from sx, styleOverrides.extended or a theme variant took effect. Now this minHeight wins, and so do the 34 and 40 below for the small and medium sizes:

  • <Fab variant="extended" sx={{ height: 30 }}>: 30 → 48
  • <Fab variant="extended" size="small" sx={{ height: 28 }}>: 28 → 34

Custom sizes added through module augmentation are hit hardest. No built-in variant matches them, so they inherit minHeight: 48 and padding: '8px 16px'. A custom xsmall size with height: 28 renders at 48.

Users can fix it by also setting minHeight, but nothing warns them, so their layouts just change. I don't see a CSS approach that grows with the content and still keeps a smaller explicit height. So I think this has to be called out as a breaking change, with a changelog entry and a migration note, or held for the next major. Please also update the PR description, which currently says nothing moves.

},
},
{
props: { variant: 'extended', size: 'small' },
style: {
width: 'auto',
padding: '0 8px',
padding: '2px 8px',
borderRadius: 34 / 2,
minWidth: 34,
height: 34,
minHeight: 34,
},
},
{
props: { variant: 'extended', size: 'medium' },
style: {
width: 'auto',
padding: '0 16px',
padding: '4px 16px',
borderRadius: 40 / 2,
minWidth: 40,
height: 40,
minHeight: 40,
},
},
{
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53 changes: 53 additions & 0 deletions packages/mui-material/src/Fab/Fab.test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -97,6 +97,59 @@ describe('<Fab />', () => {
expect(button).to.have.class(classes.sizeMedium);
});

// JSDOM does no layout, so the one-line heights are only measurable in a real
// browser. The content is 1.75em tall whatever the font family, so these are
// the minimums rather than anything font-dependent.
it.skipIf(isJsdom())('keeps the one-line height of each extended size', () => {
render(
<React.Fragment>
<Fab variant="extended" data-testid="large">
Save
</Fab>
<Fab variant="extended" size="medium" data-testid="medium">
Save
</Fab>
<Fab variant="extended" size="small" data-testid="small">
Save
</Fab>
</React.Fragment>,
);

expect(screen.getByTestId('large').getBoundingClientRect().height).to.equal(48);
expect(screen.getByTestId('medium').getBoundingClientRect().height).to.equal(40);
expect(screen.getByTestId('small').getBoundingClientRect().height).to.equal(34);
});

it.skipIf(isJsdom())('does not stretch to fill a flex parent', () => {
render(
<div style={{ display: 'flex', height: 160 }}>
<Fab variant="extended">Save</Fab>
</div>,
);

expect(screen.getByRole('button').getBoundingClientRect().height).to.equal(48);
});

// JSDOM does no layout, so the overflow this guards against is only visible
// in a real browser.
it.skipIf(isJsdom())('keeps a wrapping label inside the extended button', () => {

@ZeeshanTamboli ZeeshanTamboli Oct 26, 2026

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This only covers the large size, and no test checks that a one-line label keeps its height. Could you add:

  • a check that a one-line label measures 48, 40 and 34px for the large, medium and small sizes
  • a check that a flex parent doesn't stretch the Fab, so the regression flagged in Fab.js can't come back. This one fails on the current branch, which measures 100px:
it.skipIf(isJsdom())('is not stretched by a flex parent', () => {
  render(
    <div style={{ display: 'flex', height: 100 }}>
      <Fab variant="extended">Add</Fab>
    </div>,
  );
  expect(screen.getByRole('button').getBoundingClientRect().height).to.equal(48);
});

render(
<div style={{ width: 120 }}>
<Fab variant="extended">
<span data-testid="label">Create new deployment</span>
</Fab>
</div>,
);

const fab = screen.getByRole('button').getBoundingClientRect();
const label = screen.getByTestId('label').getBoundingClientRect();

// The button grew past its one-line height, so the label wrapped.
expect(fab.height).to.be.greaterThan(48);
expect(label.top).to.be.at.least(fab.top);
expect(label.bottom).to.be.at.most(fab.bottom);
});

it('should have a ripple', async () => {
const { container } = render(<Fab>Fab</Fab>);
await ripple.startTouch(screen.getByRole('button'));
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