Print file path in detailed errors when jumping files (chapel-lang#23520

)

This aims to resolve chapel-lang#21656.

Though I've read Brad's opinion on the various sketches, I am not
inclined to put the filename on the same line as the previous error
message. The reason for this is that it doesn't mesh well with the
current approach we take (each piece of the error message is a distinct
call that writes text to a stream). To be able to splice the file from
code output back into the line before it, we'd need the code that prints
the error message to be coupled with the code that prints the lines of
Chapel. Furthermore, the approach is not resilient to non-standard
phrasing of the message above (it modifies them grammatically!).

Thus, I've taken the approach of Rust error messages, and print the
filename with an `-->` character. I think using delimiters makes the
filename less likely to blend in with the sentence above (and, like I
described above, actually making it blend in properly is hard).

The error message from the issue now looks as follows:

<img width="368" alt="Screen Shot 2023-09-21 at 5 08 18 PM"
src="https://github.com/chapel-lang/chapel/assets/4361282/4ba23642-0453-4807-b928-43916ca4c569">

Reviewed by @mppf -- thanks!

## Testing
- [x] paratest

frontend/include/chpl/framework/ErrorWriter.h

@@ -393,6 +393,15 @@ class ErrorWriter : public ErrorWriterBase {
   std::ostream& oss_;
   ErrorWriterBase::OutputFormat outputFormat_;
   bool useColor_;
+  std::string lastFilePath_;
+
+  /* Called when the error tries to print a particular file path to indicate
+     the location of an error. Returns true if this is needed, which happens
+     when the previously-printed file path was different. Otherwise,
+     the error message can skip printing file path information, since
+     it has not changed.
+   */
+  bool noteFilePath(std::string newPath);
 
   void setColor(TermColorName color);
 

frontend/lib/framework/ErrorWriter.cpp

@@ -78,6 +78,12 @@ static std::string fileText(Context* context, const Location& loc) {
   return fileText.text();
 }
 
+bool ErrorWriter::noteFilePath(std::string newPath) {
+  bool toReturn = lastFilePath_ != newPath;
+  lastFilePath_ = std::move(newPath);
+  return toReturn;
+}
+
 void ErrorWriter::setColor(TermColorName color) {
   if (useColor_) {
     oss_ << getColorFormat(color);
@@ -104,18 +110,29 @@ static TermColorName kindColor(ErrorBase::Kind kind) {
   return CLEAR;
 }
 
-static void writeFile(Context* context,
-                      std::ostream& oss,
-                      const Location& loc) {
+static std::string locToPath(Context* context, const Location& loc) {
   UniqueString pathUstr = loc.path();
   if (context) pathUstr = context->adjustPathForErrorMsg(pathUstr);
   auto path = pathUstr.c_str();
-  int lineno = loc.line();
   bool validPath = (path != nullptr && path[0] != '\0');
+  if (validPath) return path;
+  return "";
+}
+
+static void writeFile(Context* context,
+                      std::ostream& oss,
+                      const Location& loc,
+                      std::string* outFilePath = nullptr) {
+  int lineno = loc.line();
+  auto path = locToPath(context, loc);
+  if (outFilePath) *outFilePath = path;
 
-  if (validPath && lineno > 0) oss << path << ":" << lineno;
-  else if (validPath) oss << path;
-  else oss << "(unknown location)";
+  if (!path.empty()) {
+    if (lineno > 0) oss << path << ":" << lineno;
+    else oss << path;
+  } else {
+    oss << "(unknown location)";
+  }
 }
 
 void ErrorWriter::writeHeading(ErrorBase::Kind kind, ErrorType type,
@@ -129,7 +146,13 @@ void ErrorWriter::writeHeading(ErrorBase::Kind kind, ErrorType type,
   oss_ << kindText(kind);
   setColor(CLEAR);
   oss_ << " in ";
-  writeFile(context, oss_, errordetail::locate(context, loc));
+
+  // Printing the header prints the file path, so we need to update the
+  // 'lastFilePath_' field.
+  std::string printedPath;
+  writeFile(context, oss_, errordetail::locate(context, loc), &printedPath);
+  noteFilePath(std::move(printedPath));
+
   if (outputFormat_ == DETAILED) {
     // Second part of the error decoration
     const char* name = ErrorBase::getTypeName(type);
@@ -207,6 +230,14 @@ void ErrorWriter::writeCode(const Location& location,
   size_t codeIndent = gutterSize+3;
   int lineNumber = location.firstLine();
 
+  // Print the file path if it's changed since the last code block. Printing
+  // a code block will display the file path if needed, so lastFilePath_ needs
+  // to be updated.
+  if (noteFilePath(locToPath(context, location))) {
+    printBlank(oss_, codeIndent - 1);
+    oss_ << "--> " << lastFilePath_ << std::endl;
+  }
+
   printBlank(oss_, codeIndent);
   oss_ << "|";
   oss_ << std::endl;