Fit subviews that are larger than the proposed size

Author: tevelee

Sources/Flow/Internal/Layout.swift

@@ -118,8 +118,14 @@ struct FlowLayout: Sendable {
         of subviews: some Subviews,
         cache: FlowLayoutCache
     ) -> Lines {
-        let sizes = cache.subviewsCache.map(\.ideal)
-        let spacings = if let itemSpacing {
+        let sizes: [Size] = zip(cache.subviewsCache, subviews).map { cache, subview in
+            if cache.ideal.fits(in: proposedSize) {
+                cache.ideal
+            } else {
+                subview.sizeThatFits(proposedSize).size(on: axis)
+            }
+        }
+        let spacings: [CGFloat] = if let itemSpacing {
             [0] + Array(repeating: itemSpacing, count: subviews.count - 1)
         } else {
             [0] + cache.subviewsCache.adjacentPairs().map { lhs, rhs in
@@ -133,7 +139,7 @@ struct FlowLayout: Sendable {
             FlowLineBreaker()
         }
 
-        let breakpoints = lineBreaker.wrapItemsToLines(
+        let breakpoints: [Int] = lineBreaker.wrapItemsToLines(
             sizes: sizes.map(\.breadth),
             spacings: spacings,
             in: proposedSize.replacingUnspecifiedDimensions(by: .infinity).value(on: axis)
@@ -185,6 +191,8 @@ struct FlowLayout: Sendable {
         let sumOfIdeal = subviewsInPriorityOrder.sum { $0.spacing + $0.cache.ideal.breadth }
         var remainingSpace = proposedSize.value(on: axis) - sumOfIdeal
 
+        guard remainingSpace > 0 else { return }
+
         if justification.isStretchingItems {
             let sumOfMax = subviewsInPriorityOrder.sum { $0.spacing + $0.cache.max.breadth }
             let potentialGrowth = sumOfMax - sumOfIdeal

Sources/Flow/Internal/Size.swift

@@ -34,6 +34,17 @@ struct Size: Sendable {
             case .vertical: \.depth
         }
     }
+
+    @usableFromInline
+    func fits(in proposedSize: ProposedViewSize) -> Bool {
+        if let proposedWidth = proposedSize.width, self[.horizontal] > proposedWidth {
+            return false
+        }
+        if let proposedHeight = proposedSize.height, self[.vertical] > proposedHeight {
+            return false
+        }
+        return true
+    }
 }
 
 extension Axis {

Tests/FlowTests/FlowTests.swift

@@ -325,4 +325,21 @@ final class FlowTests: XCTestCase {
         +------+
         """)
     }
+
+    func test_HFlow_text() {
+        // Given
+        let sut: FlowLayout = .horizontal(alignment: .center, itemSpacing: 1, lineSpacing: 0)
+
+        // When
+        let result = sut.layout([WrappingText(size: 6×1), 1×1, 1×1, 1×1], in: 5×3)
+
+        // Then
+        XCTAssertEqual(render(result), """
+        +-----+
+        |XXXXX|
+        |XXXXX|
+        |X X X|
+        +-----+
+        """)
+    }
 }

Tests/FlowTests/Utils/TestSubview.swift

@@ -2,7 +2,7 @@ import SwiftUI
 import XCTest
 @testable import Flow
 
-final class TestSubview: Flow.Subview, CustomStringConvertible {
+class TestSubview: Flow.Subview, CustomStringConvertible {
     var spacing = ViewSpacing()
     var priority: Double = 1
     var placement: (position: CGPoint, size: CGSize)?
@@ -58,7 +58,22 @@ final class TestSubview: Flow.Subview, CustomStringConvertible {
     }
 }
 
-extension [TestSubview]: Subviews {}
+final class WrappingText: TestSubview {
+    override func sizeThatFits(_ proposal: ProposedViewSize) -> CGSize {
+        let area = idealSize.width * idealSize.height
+        if let proposedWidth = proposal.width, idealSize.width > proposedWidth {
+            let height = (Int(1)...).first { area <= proposedWidth * CGFloat($0) }!
+            return CGSize(width: proposedWidth, height: CGFloat(height))
+        }
+        if let proposedHeight = proposal.height, idealSize.height > proposedHeight {
+            let width = (Int(1)...).first { area <= proposedHeight * CGFloat($0) }!
+            return CGSize(width: CGFloat(width), height: proposedHeight)
+        }
+        return super.sizeThatFits(proposal)
+    }
+}
+
+extension [TestSubview]: Flow.Subviews {}
 
 typealias LayoutDescription = (subviews: [TestSubview], reportedSize: CGSize)
 
@@ -92,6 +107,8 @@ func render(_ layout: LayoutDescription, border: Bool = true) -> String {
     struct Point: Hashable {
         let x, y: Int
     }
+    let width = Int(layout.reportedSize.width)
+    let height = Int(layout.reportedSize.height)
 
     var positions: Set<Point> = []
     for view in layout.subviews {
@@ -101,14 +118,13 @@ func render(_ layout: LayoutDescription, border: Bool = true) -> String {
                 for x in Int(point.x) ..< Int(point.x + placement.size.width) {
                     let result = positions.insert(Point(x: x, y: y))
                     precondition(result.inserted, "Boxes should not overlap")
+                    precondition(x >= 0 && x < width && y >= 0 && y < height, "Out of bounds")
                 }
             }
         } else {
             fatalError("Should be placed")
         }
     }
-    let width = Int(layout.reportedSize.width)
-    let height = Int(layout.reportedSize.height)
     var result = ""
     if border {
         result += "+" + String(repeating: "-", count: width) + "+\n"