Merge pull request #10 from llvm-swift/scanl

Improve failure message with location of last scan

Author: CodaFi

Sources/FileCheck/CheckString.swift

@@ -301,6 +301,9 @@ struct CheckString {
   }
 }
 
+private let whitespaceCharacterSet: Set<Character> = [" ", "\t", "\n", "\r"]
+
+
 private func diagnoseFailedCheck(
   _ pattern: Pattern, _ loc: CheckLocation, _ prefix: String,
   _ variableTable: [String : String], _ options: FileCheckOptions,
@@ -334,6 +337,12 @@ private func diagnoseFailedCheck(
     )
   }
 
+  let bufferPrefix = buffer.firstIndex { !whitespaceCharacterSet.contains($0) } ?? buffer.startIndex
+  diagnose(.note,
+           at: .string(String(buffer[bufferPrefix...])),
+           with: "scanning from here",
+           options: options)
+
   // Note any variables used by the pattern
   for (varName, _) in pattern.variableUses {
     if varName.first == "@" {

Tests/FileCheckTests/FileCheckSpec.swift

@@ -151,7 +151,9 @@ class FileCheckSpec : XCTestCase {
     XCTAssert(fileCheckOutput(of: .stdout, withPrefixes: ["CHECK-NEAREST-PATTERN-MSG"]) {
       // CHECK-NEAREST-PATTERN-MSG: error: {{.*}}: could not find 'Once more into the beach' in input
       // CHECK-NEAREST-PATTERN-MSG-NEXT: // {{.*}}: Once more into the beach
-      // CHECK-NEAREST-PATTERN-MSG-NEXT: note: possible intended match here
+      // CHECK-NEAREST-PATTERN-MSG-NEXT: note: scanning from here
+      // CHECK-NEAREST-PATTERN-MSG-NEXT: Once more into the breach
+      // CHECK-NEAREST-PATTERN-MSG: note: possible intended match here
       // CHECK-NEAREST-PATTERN-MSG-NEXT: Once more into the breach
       XCTAssertFalse(fileCheckOutput(of: .stdout, withPrefixes: ["CHECK-NEAREST-PATTERN"], options: [.disableColors]) {
         // CHECK-NEAREST-PATTERN: Once more into the beach