Use bold without colors for diagnostic text

Match the existing LLVM style used by the Swift compiler, where the
diagnostic severity (warning, note, error) is colorized and bolded,
but the diagnostic text is bolded but in the default color. Visually,
this is less overwhelming, which is presumably why the compiler has
been doing it.

Author: DougGregor

Sources/SwiftDiagnostics/DiagnosticsFormatter.swift

@@ -321,26 +321,31 @@ public struct DiagnosticsFormatter {
   /// Annotates the given ``DiagnosticMessage`` with an appropriate ANSI color code (if the value of the `colorize`
   /// property is `true`) and returns the result as a printable string.
   func colorizeIfRequested(_ message: DiagnosticMessage) -> String {
-    switch message.severity {
+    colorizeIfRequested(severity: message.severity, message: message.message)
+  }
+
+  /// Annotates a diagnostic message with the given severity and text with an appropriate ANSI color code.
+  func colorizeIfRequested(severity: DiagnosticSeverity, message: String) -> String {
+    let severityText: String
+    let severityAnnotation: ANSIAnnotation
+
+    switch severity {
     case .error:
-      let annotation = ANSIAnnotation(color: .red, trait: .bold)
-      return colorizeIfRequested("error: \(message.message)", annotation: annotation)
+      severityText = "error"
+      severityAnnotation = .errorText
 
     case .warning:
-      let color = ANSIAnnotation(color: .yellow)
-      let prefix = colorizeIfRequested("warning: ", annotation: color.withTrait(.bold))
+      severityText = "warning"
+      severityAnnotation = .warningText
 
-      return prefix + colorizeIfRequested(message.message, annotation: color);
     case .note:
-      return colorizeNoteIfRequested(message.message)
+      severityText = "note"
+      severityAnnotation = .noteText
     }
-  }
 
-  /// Annotate a note with an appropriate ANSI color code (if requested).
-  func colorizeNoteIfRequested(_ message: String) -> String {
-    let color = ANSIAnnotation(color: .default, trait: .bold)
-    let prefix = colorizeIfRequested("note: ", annotation: color)
-    return prefix + message
+    let prefix = colorizeIfRequested("\(severityText): ", annotation: severityAnnotation)
+
+    return prefix + colorizeIfRequested(message, annotation: .diagnosticText);
   }
 
   /// Apply the given color and trait to the specified text, when we are
@@ -418,4 +423,20 @@ struct ANSIAnnotation {
   static var sourceHighlight: ANSIAnnotation {
     ANSIAnnotation(color: .default, trait: .underline)
   }
+
+  static var diagnosticText: ANSIAnnotation {
+    ANSIAnnotation(color: .default, trait: .bold)
+  }
+
+  static var errorText: ANSIAnnotation {
+    ANSIAnnotation(color: .red, trait: .bold)
+  }
+
+  static var warningText: ANSIAnnotation {
+    ANSIAnnotation(color: .yellow, trait: .bold)
+  }
+
+  static var noteText: ANSIAnnotation {
+    ANSIAnnotation(color: .default, trait: .bold)
+  }
 }

Sources/SwiftDiagnostics/GroupedDiagnostics.swift

@@ -214,7 +214,8 @@ extension GroupedDiagnostics {
 
           if rootSourceID == sourceFileID {
             let bufferLoc = slc.location(for: rootPosition)
-            prefixString += "╰─ \(bufferLoc.file):\(bufferLoc.line):\(bufferLoc.column): \(formatter.colorizeNoteIfRequested("expanded code originates here"))\n"
+            let coloredMessage = formatter.colorizeIfRequested(severity: .note, message: "expanded code originates here")
+            prefixString += "╰─ \(bufferLoc.file):\(bufferLoc.line):\(bufferLoc.column): \(coloredMessage)\n"
           }
         }
       } else {

Tests/SwiftDiagnosticsTest/DiagnosticsFormatterTests.swift

@@ -101,7 +101,7 @@ final class DiagnosticsFormatterTests: XCTestCase {
 
     let expectedOutput = """
       \u{001B}[0;36m1 │\u{001B}[0;0m var foo = bar +
-        \u{001B}[0;36m│\u{001B}[0;0m                ╰─ \u{001B}[1;31merror: expected expression after operator\u{001B}[0;0m
+        \u{001B}[0;36m│\u{001B}[0;0m                ╰─ \u{001B}[1;31merror: \u{001B}[0;0m\u{001B}[1;39mexpected expression after operator\u{001B}[0;0m
 
       """
     assertStringsEqualWithDiff(annotate(source: source, colorize: true), expectedOutput)
@@ -113,9 +113,9 @@ final class DiagnosticsFormatterTests: XCTestCase {
       """
     let expectedOutput = """
       \u{001B}[0;36m1 │\u{001B}[0;0m foo.[].[].[]
-        \u{001B}[0;36m│\u{001B}[0;0m     │  │  ╰─ \u{001B}[1;31merror: expected name in member access\u{001B}[0;0m
-        \u{001B}[0;36m│\u{001B}[0;0m     │  ╰─ \u{001B}[1;31merror: expected name in member access\u{001B}[0;0m
-        \u{001B}[0;36m│\u{001B}[0;0m     ╰─ \u{001B}[1;31merror: expected name in member access\u{001B}[0;0m
+        \u{001B}[0;36m│\u{001B}[0;0m     │  │  ╰─ \u{001B}[1;31merror: \u{001B}[0;0m\u{001B}[1;39mexpected name in member access\u{001B}[0;0m
+        \u{001B}[0;36m│\u{001B}[0;0m     │  ╰─ \u{001B}[1;31merror: \u{001B}[0;0m\u{001B}[1;39mexpected name in member access\u{001B}[0;0m
+        \u{001B}[0;36m│\u{001B}[0;0m     ╰─ \u{001B}[1;31merror: \u{001B}[0;0m\u{001B}[1;39mexpected name in member access\u{001B}[0;0m
 
       """
     assertStringsEqualWithDiff(annotate(source: source, colorize: true), expectedOutput)
@@ -128,8 +128,8 @@ final class DiagnosticsFormatterTests: XCTestCase {
 
     let expectedOutput = """
       \u{001B}[0;36m1 │\u{001B}[0;0m for \u{001B}[4;39m(i\u{001B}[0;0m \u{001B}[4;39m= 🐮; i != 👩‍👩‍👦‍👦; i += 1)\u{001B}[0;0m { }
-        \u{001B}[0;36m│\u{001B}[0;0m │      ╰─ \u{001B}[1;31merror: expected ')' to end tuple pattern\u{001B}[0;0m
-        \u{001B}[0;36m│\u{001B}[0;0m ╰─ \u{001B}[1;31merror: C-style for statement has been removed in Swift 3\u{001B}[0;0m
+        \u{001B}[0;36m│\u{001B}[0;0m │      ╰─ \u{001B}[1;31merror: \u{001B}[0;0m\u{001B}[1;39mexpected ')' to end tuple pattern\u{001B}[0;0m
+        \u{001B}[0;36m│\u{001B}[0;0m ╰─ \u{001B}[1;31merror: \u{001B}[0;0m\u{001B}[1;39mC-style for statement has been removed in Swift 3\u{001B}[0;0m
 
       """