By curiosity, it couldn't be CGFloat(acos(x.double)) instead of CGFloat(acos(Double(x.native)))?

[edit]
Nevermind, Parkera explained it should be like that because:

I don't like phrasing this as a type conversion hidden as a property.

@johnno1962, actually, this PR should not be necessary for any 32-bit platform. See:

https://github.com/apple/swift/blob/1d4a9707d6facd99b749e3bc9005e8542959ebc4/stdlib/public/Platform/tgmath.swift.gyb

This overlay renames acosf to acos, etc., so that CGFloat(acos(x.native)) is correct regardless of whether x.native is 32-bit or 64-bit. So something is wrong if the Android port won't compile, as the existing code should work.

This is what @phausler has been saying all along. So something is wrong with my/the Android swift toolchain/stdlib? Any ideas? I followed the recipe here: https://github.com/apple/swift/blob/master/docs/Android.md.. Rebuilding from scratch...

Hmm. I'm not in a position to try this myself, but:

• Can you follow that recipe and compile a "hello world"?
• Can you follow that recipe and compile a "hello world" with "print(acos(0.5 as Float))"?

If both of those work but "print(acos(CGFloat(0.5 as Float).native))" doesn't, then the code might be missing an "#if os(Android)" somewhere in CGFloat or a related file; otherwise, if one of those steps doesn't work, it's might be a similar problem with Float, the tgmath overlay, or something else in that arena...

I think, this is because Glibc is not imported for Android.

@johnno1962
Could you try adding || os(Android) there?

Oh, you already tried that in #622. Never mind.

(based on #632)
But, forcing to use Float for CGFloat.NativeType works as expected on my Ubuntu.
master...rintaro:cgfloat-forcefloat
If tgmath functions don't work in 32bit environment or Android, we might be missing something.

A bit of trouble with the rebuild:
/home/johnno/Swift/swift/stdlib/public/Platform/Glibc.swift:13:19: error: no such module 'SwiftGlibc'
@_exported import SwiftGlibc // Clang module
^
Had to copy glib.modulemap across from Ninja-ReleaseAssert/swift-linux-x86_64/lib/swift/linux/x86_64/glibc.modulemap, then it regenerated for Android anyway..

A little more progress. After a complete rebuild the CGFloat.swift problems have disappeared while the NSGeometry.swift casting is still required as values are being assigned from a Float to a Double on 32 bits despite tgmath adapting to the argument type.

Something like #632 is probably required.

Foundation/NSGeometry.swift:464:40: error: cannot convert value of type 'CGFloat.NativeType' (aka 'Float') to expected argument type 'Double'
width = floor(aRect.size.width.native)
~~~~~~~~~~~~~~~~~^~~~~~
Double( )
Foundation/NSGeometry.swift:468:42: error: cannot convert value of type 'CGFloat.NativeType' (aka 'Float') to expected argument type 'Double'
height = floor(aRect.size.height.native)
~~~~~~~~~~~~~~~~~~^~~~~~
Double( )
Foundation/NSGeometry.swift:472:39: error: cannot convert value of type 'CGFloat.NativeType' (aka 'Float') to expected argument type 'Double'
width = ceil(aRect.size.width.native)
~~~~~~~~~~~~~~~~~^~~~~~
Double( )
Foundation/NSGeometry.swift:476:41: error: cannot convert value of type 'CGFloat.NativeType' (aka 'Float') to expected argument type 'Double'
height = ceil(aRect.size.height.native)
~~~~~~~~~~~~~~~~~~^~~~~~
Double( )
Foundation/NSGeometry.swift:480:40: error: cannot convert value of type 'CGFloat.NativeType' (aka 'Float') to expected argument type 'Double'
width = round(aRect.size.width.native)
~~~~~~~~~~~~~~~~~^~~~~~
Double( )
Foundation/NSGeometry.swift:484:42: error: cannot convert value of type 'CGFloat.NativeType' (aka 'Float') to expected argument type 'Double'
height = round(aRect.size.height.native)
~~~~~~~~~~~~~~~~~~^~~~~~
Double( )
Foundation/NSGeometry.swift:490:36: error: cannot convert value of type 'CGFloat.NativeType' (aka 'Float') to expected argument type 'Double'
minX = ceil(aRect.origin.x.native)
~~~~~~~~~~~~~~~^~~~~~
Double( )
Foundation/NSGeometry.swift:494:36: error: cannot convert value of type 'CGFloat.NativeType' (aka 'Float') to expected argument type 'Double'
minY = ceil(aRect.origin.y.native)
~~~~~~~~~~~~~~~^~~~~~
Double( )
Foundation/NSGeometry.swift:498:44: error: binary operator '+' cannot be applied to two 'CGFloat.NativeType' (aka 'Float') operands
maxX = floor(aRect.origin.x.native + aRect.size.width.native)
~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~
Foundation/NSGeometry.swift:498:44: note: expected an argument list of type '(Double, Double)'
maxX = floor(aRect.origin.x.native + aRect.size.width.native)
^
Foundation/NSGeometry.swift:502:44: error: binary operator '+' cannot be applied to two 'CGFloat.NativeType' (aka 'Float') operands
maxY = floor(aRect.origin.y.native + aRect.size.height.native)
~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~
Foundation/NSGeometry.swift:502:44: note: expected an argument list of type '(Double, Double)'
maxY = floor(aRect.origin.y.native + aRect.size.height.native)
^
Foundation/NSGeometry.swift:508:37: error: cannot convert value of type 'CGFloat.NativeType' (aka 'Float') to expected argument type 'Double'
minX = floor(aRect.origin.x.native)
~~~~~~~~~~~~~~~^~~~~~
Double( )
Foundation/NSGeometry.swift:512:37: error: cannot convert value of type 'CGFloat.NativeType' (aka 'Float') to expected argument type 'Double'
minY = floor(aRect.origin.y.native)
~~~~~~~~~~~~~~~^~~~~~
Double( )
Foundation/NSGeometry.swift:516:43: error: binary operator '+' cannot be applied to two 'CGFloat.NativeType' (aka 'Float') operands
maxX = ceil(aRect.origin.x.native + aRect.size.width.native)
~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~
Foundation/NSGeometry.swift:516:43: note: expected an argument list of type '(Double, Double)'
maxX = ceil(aRect.origin.x.native + aRect.size.width.native)
^
Foundation/NSGeometry.swift:520:43: error: binary operator '+' cannot be applied to two 'CGFloat.NativeType' (aka 'Float') operands
maxY = ceil(aRect.origin.y.native + aRect.size.height.native)
~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~
Foundation/NSGeometry.swift:520:43: note: expected an argument list of type '(Double, Double)'
maxY = ceil(aRect.origin.y.native + aRect.size.height.native)
^
Foundation/NSGeometry.swift:526:37: error: cannot convert value of type 'CGFloat.NativeType' (aka 'Float') to expected argument type 'Double'

Closed in favour of #632 which builds for me on Android & #631. CGFloat.swift changes are not required after complete rebuild of toolchain from master.