Add ~ space support and complex formula tests

Agent-Logs-Url: https://github.com/wesleyel/swiftui-math/sessions/6740d67f-473b-43b8-87ba-25d9469f5757

Co-authored-by: wesleyel <48174882+wesleyel@users.noreply.github.com>

Sources/SwiftUIMath/Internal/Syntax/AtomFactory.swift

@@ -537,8 +537,10 @@ extension Math {
         return atom(fromAccentedCharacter: ch)
       case _ where ch.utf32 < 0x0021 || ch.utf32 > 0x007E:
         return nil
-      case "$", "%", "#", "&", "~", "\'", "^", "_", "{", "}", "\\":
+      case "$", "%", "#", "&", "\'", "^", "_", "{", "}", "\\":
         return nil
+      case "~":
+        return Space(amount: 3)
       case "(", "[":
         return Atom(type: .open, nucleus: stringValue)
       case ")", "]", "!", "?":

Tests/SwiftUIMathTests/Internal/Syntax/ParserTests.swift

@@ -2568,4 +2568,41 @@ struct ParserTests {
     }
   }
 
+  @Test
+  func complexFormulas() throws {
+    // Formula 1: limit with integral in denominator, using \mathrm{~d} for the differential
+    let formula1 =
+      "\\lim _{x \\rightarrow 0} \\frac{a x-\\sin x}{\\int_{b}^{x} \\frac{\\ln \\left(1+t^{3}\\right)}{t} \\mathrm{~d} t}=c, c \\neq 0"
+    // Formula 2: double sum with nested fractions and grouped terms
+    let formula2 =
+      "\\lim _{n \\rightarrow \\infty} \\sum_{i=1}^{n} \\sum_{j=1}^{n} \\frac{n}{(n+i)\\left(n^{2}+j^{2}\\right)}="
+    // Formula 3: nested integrals with arctan and \mathrm{d} differentials
+    let formula3 =
+      "\\lim _{x \\rightarrow 0} \\frac{\\int_{0}^{x}\\left[\\int_{0}^{u^{2}} \\arctan (1+t) \\mathrm{d} t\\right] \\mathrm{d} u}{x(1-\\cos x)}"
+
+    for formula in [formula1, formula2, formula3] {
+      var error: Math.ParserError? = nil
+      let list = Math.Parser.build(fromString: formula, error: &error)
+      #expect(error == nil, "Unexpected parse error for formula: \(formula)")
+      let unwrappedList = try #require(list)
+      #expect(!unwrappedList.atoms.isEmpty)
+    }
+  }
+
+  @Test
+  func tildeAsSpace() throws {
+    // ~ in math mode should produce a thin space, not an error
+    let testCases: [(String, String)] = [
+      ("a~b", "a\\, b"),
+      ("\\mathrm{~d}", "\\mathrm{\\, d}"),
+    ]
+    for (input, expected) in testCases {
+      var error: Math.ParserError? = nil
+      let list = Math.Parser.build(fromString: input, error: &error)
+      #expect(error == nil)
+      let latex = Math.Parser.atomListToString(list)
+      #expect(latex == expected, "Round-trip mismatch for input '\(input)'")
+    }
+  }
+
 }

Tests/SwiftUIMathTests/MathTests.swift

@@ -74,6 +74,33 @@
       assertSnapshot(of: view, as: .image(layout: layout))
     }
 
+    @Test
+    func complexIntegralFormulas() {
+      let view = VStack(alignment: .leading, spacing: 16) {
+        Math(
+          "\\lim _{x \\rightarrow 0} \\frac{a x-\\sin x}{\\int_{b}^{x} \\frac{\\ln \\left(1+t^{3}\\right)}{t} \\mathrm{~d} t}=c, c \\neq 0"
+        )
+        .mathTypesettingStyle(.display)
+        .mathFont(Math.Font(name: .latinModern, size: 20))
+
+        Math(
+          "\\lim _{n \\rightarrow \\infty} \\sum_{i=1}^{n} \\sum_{j=1}^{n} \\frac{n}{(n+i)\\left(n^{2}+j^{2}\\right)}="
+        )
+        .mathTypesettingStyle(.display)
+        .mathFont(Math.Font(name: .latinModern, size: 20))
+
+        Math(
+          "\\lim _{x \\rightarrow 0} \\frac{\\int_{0}^{x}\\left[\\int_{0}^{u^{2}} \\arctan (1+t) \\mathrm{d} t\\right] \\mathrm{d} u}{x(1-\\cos x)}"
+        )
+        .mathTypesettingStyle(.display)
+        .mathFont(Math.Font(name: .latinModern, size: 20))
+      }
+      .background(Color.guide)
+      .padding(.horizontal)
+
+      assertSnapshot(of: view, as: .image(layout: layout))
+    }
+
     @Test
     func inlineTextWrapping() {
       let view = VStack(alignment: .leading, spacing: 16) {