compiler: Reworked Preprocessor To Support Better Error Messages

Can now support showing the trail of includes in an error
message.

Signed-off-by: Will Hawkins <hawkinsw@obs.cr>

Sources/Common/SourceCode.swift

@@ -101,14 +101,21 @@ public struct SourceManager {
 public struct FileSourceLocation: Equatable, CustomStringConvertible {
   let location: SourceLocation
   let path: FilePath
+  let whence: Int?
   let nested: [FileSourceLocation]
 
   public init(
-    _ location: SourceLocation, _ path: FilePath, _ nested: [FileSourceLocation] = Array()
+    _ location: SourceLocation, _ path: FilePath, _ whence: Int? = .none,
+    _ nested: [FileSourceLocation] = Array()
   ) {
     self.location = location
     self.path = path
     self.nested = nested
+    self.whence = whence
+  }
+
+  public func update(whence: Int) -> FileSourceLocation {
+    return FileSourceLocation(self.location, self.path, whence, self.nested)
   }
 
   public func getLocation() -> SourceLocation {
@@ -130,7 +137,7 @@ public struct FileSourceLocation: Equatable, CustomStringConvertible {
       }).joined(separator: ",") + ")"
   }
 
-  public func pathForLocation(_ location: Int) -> FilePath? {
+  public func pathForLocation(_ location: Int) -> [FileSourceLocation]? {
 
     let queried_location = SourceLocation(location, 1)
     if !self.location.contains(queried_location) {
@@ -139,11 +146,11 @@ public struct FileSourceLocation: Equatable, CustomStringConvertible {
 
     for nested in self.nested {
       if nested.location.contains(queried_location) {
-        return nested.pathForLocation(location)
+        return [self] + nested.pathForLocation(location)!
       }
     }
 
-    return self.getPath()
+    return [self]
   }
 }
 
@@ -212,8 +219,8 @@ public struct SourceCode {
 
   public func getSourceSnippet(
     location: SourceLocation, context: Int = 0
-  ) -> (FilePath, String, String, String)? {
-    guard let path = self.pathForLocation(location.range.lowerBound) else {
+  ) -> ([FileSourceLocation], String, String, String)? {
+    guard let paths = self.pathForLocation(location.range.lowerBound) else {
       return .none
     }
     let lower = String.UTF8View.Index(utf16Offset: location.range.lowerBound, in: self.code)
@@ -234,14 +241,14 @@ public struct SourceCode {
     let result = String(self.code.utf16[lower..<upper])!
     let prior = String(self.code.utf16[prior_start..<lower])!
     let after = String(self.code.utf16[upper...after_end])!
-    return (path, result, prior, after)
+    return (paths, result, prior, after)
   }
 
   public func getLocations() -> FileSourceLocation {
     return self.locations
   }
 
-  public func pathForLocation(_ location: Int) -> FilePath? {
+  public func pathForLocation(_ location: Int) -> [FileSourceLocation]? {
     return self.locations.pathForLocation(location)
   }
 }
@@ -263,42 +270,40 @@ func do_preprocess(
             "Could not open \(file) for preprocessing"))
     }
 
-    var contents = try String.init(
+    let orig = try String.init(
       contentsOf: URL(filePath: included_path.string), encoding: String.defaultCStringEncoding)
-    var changed = true
+    var expanded = ""
+    var oloc = orig.startIndex
 
-    while changed {
-      changed = false
-      for match in contents.matches(of: re) {
+    for match in orig.matches(of: re) {
 
-        let before = contents[..<match.range.lowerBound]
-        let after = contents[match.range.upperBound...]
+      if oloc != match.range.lowerBound {
+        expanded += String(orig[oloc..<match.range.lowerBound])
+      }
+      oloc = match.range.upperBound
 
-        // By calling ourselves recursively, the include being processed will
-        // be _completely_ expanded (including any nested includes).
-        switch do_preprocess(FilePath("\(match.1)"), manager, starting + before.count) {
-        case .Ok((let location, let expanded)):
-          // Recombine what was before and after the include being processed
-          // with the expanded text.
-          contents = before + expanded + after
-          // Remember the location (and those it has nested) that were found in
-          // the expanded text.
-          locations.append(location)
-        case .Error(let e):
-          return .Error(e)
-        }
-
-        // Only process one at a time.
-        changed = true
-        break
+      // By calling ourselves recursively, the include being processed will
+      // be _completely_ expanded (including any nested includes).
+      switch do_preprocess(FilePath("\(match.1)"), manager, starting + expanded.count) {
+      case .Ok((let location, let recursively_expanded)):
+        // Recombine what was before and after the include being processed
+        // with the expanded text.
+        expanded += recursively_expanded
+        // Remember the location (and those it has nested) that were found in
+        // the expanded text.
+        locations.append(location.update(whence: match.range.lowerBound.utf16Offset(in: orig)))
+      case .Error(let e):
+        return .Error(e)
       }
     }
 
+    // Make sure that we got it all!
+    expanded += orig[oloc...]
+
     return .Ok(
       (
         FileSourceLocation(
-          SourceLocation(starting..<(starting + contents.count)), file, locations),
-        contents
+          SourceLocation(starting..<(starting + expanded.count)), file, .none, locations), expanded
       ))
 
   } catch (let e) {