SourceLocation.init should enforce valid arguments (#817)

This modifies `SourceLocation.init()` to add `precondition`s which
enforce that its arguments are valid, matching preconditions in the
corresponding properties.

### Modifications:

- Add `precondition`s to the initializer which match those in `didSet`
of the corresponding properties.
- Add precondition DocC symbol documentation where relevant.
- Adjusted existing tests which were previously invalid (although not
particularly problematic) but were not failing.

### Result:

Newly-added exit tests now pass.

### Checklist:

- [x] Code and documentation should follow the style of the [Style
Guide](https://github.com/apple/swift-testing/blob/main/Documentation/StyleGuide.md).
- [x] If public symbols are renamed or modified, DocC references should
be updated.

Author: stmontgomery

Sources/Testing/Running/Configuration.swift

@@ -75,11 +75,10 @@ public struct Configuration: Sendable {
 
     /// The maximum number of times the test run should iterate.
     ///
-    /// - Precondition: The value of this property must be greater than or equal
-    ///   to `1`.
+    /// - Precondition: The value of this property must be greater than `0`.
     public var maximumIterationCount: Int {
       willSet {
-        precondition(newValue >= 1, "Test runs must iterate at least once.")
+        precondition(newValue > 0, "Test runs must iterate at least once (maximumIterationCount was \(newValue)).")
       }
     }
 

Sources/Testing/SourceAttribution/SourceLocation.swift

@@ -12,14 +12,19 @@
 public struct SourceLocation: Sendable {
   /// The file ID of the source file.
   ///
+  /// - Precondition: The value of this property must not be empty and must be
+  ///   formatted as described in the documentation for the
+  ///   [`#fileID`](https://developer.apple.com/documentation/swift/fileID()).
+  ///   macro in the Swift standard library.
+  ///
   /// ## See Also
   ///
   /// - ``moduleName``
   /// - ``fileName``
   public var fileID: String {
-    didSet {
-      precondition(!fileID.isEmpty)
-      precondition(fileID.contains("/"))
+    willSet {
+      precondition(!newValue.isEmpty, "SourceLocation.fileID must not be empty (was \(newValue))")
+      precondition(newValue.contains("/"), "SourceLocation.fileID must be a well-formed file ID (was \(newValue))")
     }
   }
 
@@ -74,20 +79,45 @@ public struct SourceLocation: Sendable {
   public var _filePath: String
 
   /// The line in the source file.
+  ///
+  /// - Precondition: The value of this property must be greater than `0`.
   public var line: Int {
-    didSet {
-      precondition(line > 0)
+    willSet {
+      precondition(newValue > 0, "SourceLocation.line must be greater than 0 (was \(newValue))")
     }
   }
 
   /// The column in the source file.
+  ///
+  /// - Precondition: The value of this property must be greater than `0`.
   public var column: Int {
-    didSet {
-      precondition(column > 0)
+    willSet {
+      precondition(newValue > 0, "SourceLocation.column must be greater than 0 (was \(newValue))")
     }
   }
 
+  /// Initialize an instance of this type with the specified location details.
+  ///
+  /// - Parameters:
+  ///   - fileID: The file ID of the source file, using the format described in
+  ///     the documentation for the
+  ///     [`#fileID`](https://developer.apple.com/documentation/swift/fileID())
+  ///     macro in the Swift standard library.
+  ///   - filePath: The path to the source file.
+  ///   - line: The line in the source file. Must be greater than `0`.
+  ///   - column: The column in the source file. Must be greater than `0`.
+  ///
+  /// - Precondition: `fileID` must not be empty and must be formatted as
+  ///   described in the documentation for
+  ///   [`#fileID`](https://developer.apple.com/documentation/swift/fileID()).
+  /// - Precondition: `line` must be greater than `0`.
+  /// - Precondition: `column` must be greater than `0`.
   public init(fileID: String, filePath: String, line: Int, column: Int) {
+    precondition(!fileID.isEmpty, "SourceLocation.fileID must not be empty (was \(fileID))")
+    precondition(fileID.contains("/"), "SourceLocation.fileID must be a well-formed file ID (was \(fileID))")
+    precondition(line > 0, "SourceLocation.line must be greater than 0 (was \(line))")
+    precondition(column > 0, "SourceLocation.column must be greater than 0 (was \(column))")
+
     self.fileID = fileID
     self._filePath = filePath
     self.line = line

Tests/TestingTests/IssueTests.swift

@@ -1489,8 +1489,8 @@ struct IssueCodingTests {
 
   @Test func sourceLocationPropertyGetter() throws {
     let sourceLocation = SourceLocation(
-      fileID: "fileID",
-      filePath: "filePath",
+      fileID: "M/file.swift",
+      filePath: "M/file.swift",
       line: 13,
       column: 42
     )
@@ -1509,8 +1509,8 @@ struct IssueCodingTests {
 
   @Test func sourceLocationPropertySetter() throws {
     let initialSourceLocation = SourceLocation(
-      fileID: "fileID",
-      filePath: "filePath",
+      fileID: "M/file.swift",
+      filePath: "file.swift",
       line: 13,
       column: 42
     )
@@ -1523,8 +1523,8 @@ struct IssueCodingTests {
     let issue = Issue(kind: .apiMisused, sourceContext: sourceContext)
 
     let updatedSourceLocation = SourceLocation(
-      fileID: "fileID2",
-      filePath: "filePath2",
+      fileID: "M/file2.swift",
+      filePath: "file2.swift",
       line: 14,
       column: 43
     )

Tests/TestingTests/SourceLocationTests.swift

@@ -51,21 +51,6 @@ struct SourceLocationTests {
     #expect(sourceLocation.fileName == "D.swift")
   }
 
-
-#if !SWT_NO_EXIT_TESTS
-  @Test("SourceLocation.fileID property must be well-formed")
-  func sourceLocationFileIDWellFormed() async {
-    await #expect(exitsWith: .failure) {
-      var sourceLocation = #_sourceLocation
-      sourceLocation.fileID = ""
-    }
-    await #expect(exitsWith: .failure) {
-      var sourceLocation = #_sourceLocation
-      sourceLocation.fileID = "ABC"
-    }
-  }
-#endif
-
   @Test("SourceLocation.line and .column properties")
   func sourceLocationLineAndColumn() {
     var sourceLocation = #_sourceLocation
@@ -81,6 +66,34 @@ struct SourceLocationTests {
   }
 
 #if !SWT_NO_EXIT_TESTS
+  @Test("SourceLocation.init requires well-formed arguments")
+  func sourceLocationInitPreconditions() async {
+    await #expect(exitsWith: .failure, "Empty fileID") {
+      _ = SourceLocation(fileID: "", filePath: "", line: 1, column: 1)
+    }
+    await #expect(exitsWith: .failure, "Invalid fileID") {
+      _ = SourceLocation(fileID: "B.swift", filePath: "", line: 1, column: 1)
+    }
+    await #expect(exitsWith: .failure, "Zero line") {
+      _ = SourceLocation(fileID: "A/B.swift", filePath: "", line: 0, column: 1)
+    }
+    await #expect(exitsWith: .failure, "Zero column") {
+      _ = SourceLocation(fileID: "A/B.swift", filePath: "", line: 1, column: 0)
+    }
+  }
+
+  @Test("SourceLocation.fileID property must be well-formed")
+  func sourceLocationFileIDWellFormed() async {
+    await #expect(exitsWith: .failure) {
+      var sourceLocation = #_sourceLocation
+      sourceLocation.fileID = ""
+    }
+    await #expect(exitsWith: .failure) {
+      var sourceLocation = #_sourceLocation
+      sourceLocation.fileID = "ABC"
+    }
+  }
+
   @Test("SourceLocation.line and column properties must be positive")
   func sourceLocationLineAndColumnPositive() async {
     await #expect(exitsWith: .failure) {