Fix SourceMgrDiagnosticHandler::convertLocToSMLoc for unknown line/column scenerio.

[Jing]

Summary

FileLineColLoc allows the column and line to be zero to represent unknown column and/or unknown line/column information. However, SourceMgr::FindLocForLineAndColumn treats line 0 and col 0 valid and pointing to the first line and col, respectively. To adapt this mismatch in semantics, we explicitly check line/col being zeros in SourceMgrDiagnosticHandler::convertLocToSMLoc

[mehdi_amini]

mlir/lib/IR/Diagnostics.cpp

515

How do we actually identify when the loc is referring really to the beginning of the file? There isn't a way to figure out?

[Jing]

mlir/lib/IR/Diagnostics.cpp

515

SourceMgr::FindLocForLineAndColumn assumes the indices are one-based, but treats line 0 specially that also points the first line.

[mehdi_amini]

Let me know if you need me to land this for you

[Jing]

I found there are some internal tests (on diagnostics) that rely on column zero being the first column.
I am not so sure whether we should adopt that behavior and change API (i.e. treating only row zero being an unknown location) or fix the tests.

[rriddle]

In D80258#2053986, @Jing wrote:

I found there are some internal tests (on diagnostics) that rely on column zero being the first column.
I am not so sure whether we should adopt that behavior and change API (i.e. treating only row zero being an unknown location) or fix the tests.

We should just fix the tests. zero line/zero column seems like a good enough indicator that it is the beginning of the file.

mlir/lib/IR/Diagnostics.cpp

SourceMgrDiagnosticHandler::getBufferForFile(StringRef filename) {
   if (unsigned id = impl->getSourceMgrBufferIDForFile(mgr, filename))
     return mgr.getMemoryBuffer(id);
   return nullptr;
 }
 
 /// Get a memory buffer for the given file, or the main file of the source
 /// manager if one doesn't exist. This always returns non-null.
 llvm::SMLoc SourceMgrDiagnosticHandler::convertLocToSMLoc(FileLineColLoc loc) {
+  // The column and line may be zero to represent unknown column and/or unknown
+  /// line/column information.
+  if (loc.getLine() == 0 || loc.getColumn() == 0)
+    return llvm::SMLoc();
+
   unsigned bufferId = impl->getSourceMgrBufferIDForFile(mgr, loc.getFilename());
   if (!bufferId)
     return llvm::SMLoc();
   return mgr.FindLocForLineAndColumn(bufferId, loc.getLine(), loc.getColumn());
 }
 
 //===----------------------------------------------------------------------===//
 // SourceMgrDiagnosticVerifierHandler