Simplify __ExpressionID a bit

Author: grynspan

Sources/Testing/ExitTests/ExitTest.swift

@@ -294,8 +294,8 @@ func callExitTest(
 
   // Plumb the exit test's result through the general expectation machinery.
   var expectationContext = __ExpectationContext()
-  expectationContext.sourceCode[""] = sourceCode
-  expectationContext.runtimeValues[""] = { Expression.Value(reflecting: actualExitCondition) }
+  expectationContext.sourceCode[.root] = sourceCode
+  expectationContext.runtimeValues[.root] = { Expression.Value(reflecting: actualExitCondition) }
   return check(
     expectedExitCondition == actualExitCondition,
     expectationContext: expectationContext,

Sources/Testing/Expectations/ExpectationChecking+Macro.swift

@@ -237,7 +237,7 @@ public func __checkEscapedCondition(
   sourceLocation: SourceLocation
 ) -> Result<Void, any Error> {
   var expectationContext = __ExpectationContext()
-  expectationContext.sourceCode[""] = sourceCode
+  expectationContext.sourceCode[.root] = sourceCode
 
   return check(
     condition,
@@ -266,7 +266,7 @@ public func __checkEscapedCondition<T>(
   sourceLocation: SourceLocation
 ) -> Result<T, any Error> where T: ~Copyable {
   var expectationContext = __ExpectationContext()
-  expectationContext.sourceCode[""] = sourceCode
+  expectationContext.sourceCode[.root] = sourceCode
 
   let result = check(
     optionalValue != nil,
@@ -393,7 +393,7 @@ public func __checkClosureCall(
   }
 
   var expectationContext = __ExpectationContext()
-  expectationContext.sourceCode[""] = sourceCode
+  expectationContext.sourceCode[.root] = sourceCode
   return check(
     success,
     expectationContext: expectationContext,
@@ -433,7 +433,7 @@ public func __checkClosureCall(
   }
 
   var expectationContext = __ExpectationContext()
-  expectationContext.sourceCode[""] = sourceCode
+  expectationContext.sourceCode[.root] = sourceCode
   return check(
     success,
     expectationContext: expectationContext,
@@ -519,7 +519,7 @@ public func __checkClosureCall<R>(
   sourceLocation: SourceLocation
 ) -> Result<Void, any Error> {
   var expectationContext = __ExpectationContext()
-  expectationContext.sourceCode[""] = sourceCode
+  expectationContext.sourceCode[.root] = sourceCode
 
   var errorMatches = false
   var mismatchExplanationValue: String? = nil
@@ -532,7 +532,7 @@ public func __checkClosureCall<R>(
     }
     mismatchExplanationValue = explanation
   } catch {
-    expectationContext.runtimeValues[""] = { Expression.Value(reflecting: error) }
+    expectationContext.runtimeValues[.root] = { Expression.Value(reflecting: error) }
     let secondError = Issue.withErrorRecording(at: sourceLocation) {
       errorMatches = try errorMatcher(error)
     }
@@ -571,7 +571,7 @@ public func __checkClosureCall<R>(
   sourceLocation: SourceLocation
 ) async -> Result<Void, any Error> {
   var expectationContext = __ExpectationContext()
-  expectationContext.sourceCode[""] = sourceCode
+  expectationContext.sourceCode[.root] = sourceCode
 
   var errorMatches = false
   var mismatchExplanationValue: String? = nil
@@ -584,7 +584,7 @@ public func __checkClosureCall<R>(
     }
     mismatchExplanationValue = explanation
   } catch {
-    expectationContext.runtimeValues[""] = { Expression.Value(reflecting: error) }
+    expectationContext.runtimeValues[.root] = { Expression.Value(reflecting: error) }
     let secondError = await Issue.withErrorRecording(at: sourceLocation) {
       errorMatches = try await errorMatcher(error)
     }

Sources/Testing/SourceAttribution/ExpressionID.swift

@@ -17,30 +17,18 @@
 /// - Warning: This type is used to implement the `#expect()` and `#require()`
 ///   macros. Do not use it directly.
 public struct __ExpressionID: Sendable {
+  /// The ID of the root node in an expression graph.
+  static var root: Self {
+    ""
+  }
+
   /// The string produced at compile time that encodes the unique identifier of
   /// the represented expression.
   var stringValue: String
 
   /// The number of bits in a nybble.
   private static var _bitsPerNybble: Int { 4 }
 
-  /// The ID of the syntax node represented by this instance.
-  var nodeID: UInt32 {
-    // The ID is encoded as the highest non-zero bit in the string, so that's
-    // nybbles.first.highestBit + ((nybbles.count - 1) * bitsPerNybble)
-    if stringValue.isEmpty {
-      return 0
-    }
-
-    let stringNybble = stringValue[stringValue.startIndex ... stringValue.startIndex]
-    guard let nybble = UInt8(stringNybble, radix: 16) else {
-      return 0
-    }
-
-    let highestBit = UInt8.bitWidth - nybble.leadingZeroBitCount
-    return UInt32(highestBit) + UInt32((stringValue.count - 1) * Self._bitsPerNybble)
-  }
-
   /// A representation of this instance suitable for use as a key path in an
   /// instance of `Graph` where the key type is `UInt32`.
   ///