Use SourceLocationConverter for whitespace linter diagnostics.

Previously, we were scanning the input string to compute the line
and column number for diagnostics emitted by the whitespace linter
(and doing this scan for _every_ diagnostic). Since we already
have a `SourceLocationConverter` from the parsed source tree, we
can just use it instead—it's already cached a mapping from UTF-8
offsets to line/column numbers.

Author: allevato

Sources/SwiftFormatWhitespaceLinter/WhitespaceLinter.swift

@@ -201,10 +201,8 @@ public class WhitespaceLinter {
       return
     }
 
-    let pos = calculatePosition(offset: adjustedUserOffset, data: self.userText)
-
     isLineTooLong = true
-    diagnose(.lineLengthError, line: pos.line, column: pos.column, utf8Offset: 0)
+    diagnose(.lineLengthError, utf8Offset: adjustedUserOffset)
   }
 
   /// Compare user and formatted whitespace buffers, and check for indentation errors.
@@ -231,11 +229,7 @@ public class WhitespaceLinter {
         if form[0] != user[0] {
           let actual = indentation(of: user[0])
           let expected = indentation(of: form[0])
-          diagnose(
-            .indentationError(expected: expected, actual: actual),
-            line: 1,
-            column: 1,
-            utf8Offset: 0)
+          diagnose(.indentationError(expected: expected, actual: actual), utf8Offset: 0)
         }
       }
       return
@@ -245,14 +239,10 @@ public class WhitespaceLinter {
       offset += user[i].count + 1
     }
     if form.last != user.last {
-      let pos = calculatePosition(offset: userOffset + offset, data: self.userText)
       let actual = indentation(of: user.last ?? [])
       let expected = indentation(of: form.last ?? [])
       diagnose(
-        .indentationError(expected: expected, actual: actual),
-        line: pos.line,
-        column: pos.column,
-        utf8Offset: 0)
+        .indentationError(expected: expected, actual: actual), utf8Offset: userOffset + offset)
     }
   }
 
@@ -269,8 +259,7 @@ public class WhitespaceLinter {
     var offset = 0
     for i in 0..<(user.count - 1) {
       if user[i].count > 0 {
-        let pos = calculatePosition(offset: userOffset + offset, data: self.userText)
-        diagnose(.trailingWhitespaceError, line: pos.line, column: pos.column, utf8Offset: 0)
+        diagnose(.trailingWhitespaceError, utf8Offset: userOffset + offset)
       }
       offset += user[i].count + 1
     }
@@ -295,13 +284,12 @@ public class WhitespaceLinter {
     guard form.count == 1 && user.count == 1 && !isFirstCharacter else { return }
     guard form[0] != user[0] else { return }
 
-    let pos = calculatePosition(offset: userOffset, data: self.userText)
     let illegalSpacingCharacters: [UTF8.CodeUnit] = [utf8Tab]
     if illegalSpacingCharacters.contains(where: { user[0].contains($0) }) {
-      diagnose(.spacingCharError, line: pos.line, column: pos.column, utf8Offset: 0)
+      diagnose(.spacingCharError, utf8Offset: userOffset)
     } else if form[0].count != user[0].count {
       let delta = form[0].count - user[0].count
-      diagnose(.spacingError(delta), line: pos.line, column: pos.column, utf8Offset: 0)
+      diagnose(.spacingError(delta), utf8Offset: userOffset)
     }
   }
 
@@ -328,8 +316,7 @@ public class WhitespaceLinter {
     guard form.count < user.count else { return }
     var offset = 0
     for i in 0..<(user.count - form.count) {
-      let pos = calculatePosition(offset: userOffset + offset, data: self.userText)
-      diagnose(.removeLineError, line: pos.line, column: pos.column, utf8Offset: 0)
+      diagnose(.removeLineError, utf8Offset: userOffset + offset)
       offset += user[i].count + 1
     }
   }
@@ -356,10 +343,7 @@ public class WhitespaceLinter {
     userOffset: Int, user: [ArraySlice<UTF8.CodeUnit>], form: [ArraySlice<UTF8.CodeUnit>]
   ) {
     guard form.count > user.count && !isLineTooLong else { return }
-    let pos = calculatePosition(offset: userOffset, data: self.userText)
-    diagnose(
-      .addLinesError(form.count - user.count), line: pos.line, column: pos.column, utf8Offset: 0
-    )
+    diagnose(.addLinesError(form.count - user.count), utf8Offset: userOffset)
   }
 
   /// Find the next non-whitespace character in a given string, and any leading whitespace before
@@ -392,28 +376,6 @@ public class WhitespaceLinter {
     return (offset: data.count - 1, char: nil, whitespace: whitespaceBuffer)
   }
 
-  /// Given a string and a printable charater offset, calculate the line and column number.
-  ///
-  /// - Parameters:
-  ///   - offset: The printable character offset.
-  ///   - data: The input string for which we want the line and column numbers.
-  /// - Returns a tuple with the line and column numbers within `data`.
-  private func calculatePosition(offset: Int, data: [UTF8.CodeUnit]) -> (line: Int, column: Int) {
-    var line = 1
-    var column = 0
-
-    for (index, char) in data.enumerated() {
-      if char == utf8Newline {
-        line += 1
-        column = 0
-      } else {
-        column += 1
-      }
-      if index == offset { break }
-    }
-    return (line: line, column: column)
-  }
-
   /// Emits the provided diagnostic message to the DiagnosticEngine. The message will correspond to
   /// a specific location (line and column number) in the input Swift source file (`userText`).
   ///
@@ -425,18 +387,14 @@ public class WhitespaceLinter {
   ///   - actions: Used for attaching notes, highlights, etc.
   private func diagnose(
     _ message: Diagnostic.Message,
-    line: Int,
-    column: Int,
     utf8Offset: Int,
     actions: ((inout Diagnostic.Builder) -> Void)? = nil
   ) {
-    let loc = SourceLocation(
-      line: line, column: column, offset: utf8Offset, file: context.fileURL.path)
-    context.diagnosticEngine?.diagnose(
-      message,
-      location: loc,
-      actions: actions
-    )
+    guard let diagnosticEngine = context.diagnosticEngine else { return }
+
+    let absolutePosition = AbsolutePosition(utf8Offset: utf8Offset)
+    let sourceLocation = context.sourceLocationConverter.location(for: absolutePosition)
+    diagnosticEngine.diagnose(message, location: sourceLocation, actions: actions)
   }
 
   /// Returns the indentation that represents the indentation of the given whitespace, which is the

Tests/SwiftFormatWhitespaceLinterTests/WhitespaceLintTests.swift

@@ -206,7 +206,7 @@ final class WhitespaceLintTests: WhitespaceTestCase {
       """
 
     performWhitespaceLint(input: input, expected: expected)
-    XCTAssertDiagnosed(.addLinesError(1), line: 2, column: 0)
+    XCTAssertDiagnosed(.addLinesError(1), line: 1, column: 12)
     XCTAssertDiagnosed(.addLinesError(1), line: 3, column: 15)
     XCTAssertDiagnosed(.addLinesError(1), line: 3, column: 22)
   }
@@ -236,11 +236,11 @@ final class WhitespaceLintTests: WhitespaceTestCase {
       """
 
     performWhitespaceLint(input: input, expected: expected)
-    XCTAssertDiagnosed(.removeLineError, line: 2, column: 0)
-    XCTAssertDiagnosed(.removeLineError, line: 4, column: 0)
-    XCTAssertDiagnosed(.removeLineError, line: 5, column: 0)
-    XCTAssertDiagnosed(.removeLineError, line: 8, column: 0)
-    XCTAssertDiagnosed(.removeLineError, line: 9, column: 0)
+    XCTAssertDiagnosed(.removeLineError, line: 1, column: 12)
+    XCTAssertDiagnosed(.removeLineError, line: 3, column: 14)
+    XCTAssertDiagnosed(.removeLineError, line: 4, column: 1)
+    XCTAssertDiagnosed(.removeLineError, line: 7, column: 15)
+    XCTAssertDiagnosed(.removeLineError, line: 8, column: 19)
   }
 
   func testLineLength() {