[lldb] Fix offset calculation when printing diagnostics in multiple ranges

lldb/source/Utility/DiagnosticsRendering.cpp

@@ -112,17 +112,21 @@ void RenderDiagnosticDetails(Stream &stream,
   // Print a line with caret indicator(s) below the lldb prompt + command.
   const size_t padding = *offset_in_command;
   stream << std::string(padding, ' ');
-  size_t offset = 1;
-  for (const DiagnosticDetail &detail : remaining_details) {
-    auto &loc = *detail.source_location;
-
-    if (offset > loc.column)
-      continue;
-
-    stream << std::string(loc.column - offset, ' ') << cursor;
-    for (unsigned i = 0; i + 1 < loc.length; ++i)
-      stream << underline;
-    offset = loc.column + 1;
+  {
+    size_t x_pos = 1;
+    for (const DiagnosticDetail &detail : remaining_details) {
+      auto &loc = *detail.source_location;
+
+      if (x_pos > loc.column)
+        continue;
+
+      stream << std::string(loc.column - x_pos, ' ') << cursor;
+      ++x_pos;
+      for (unsigned i = 0; i + 1 < loc.length; ++i) {
+        stream << underline;
+        ++x_pos;
+      }
+    }
   }
   stream << '\n';
 
@@ -134,19 +138,19 @@ void RenderDiagnosticDetails(Stream &stream,
     // Get the information to print this detail and remove it from the stack.
     // Print all the lines for all the other messages first.
     stream << std::string(padding, ' ');
-    size_t offset = 1;
+    size_t x_pos = 1;
     for (auto &remaining_detail :
          llvm::ArrayRef(remaining_details).drop_back(1)) {
       uint16_t column = remaining_detail.source_location->column;
-      if (offset <= column)
-        stream << std::string(column - offset, ' ') << vbar;
-      offset = column + 1;
+      if (x_pos <= column)
+        stream << std::string(column - x_pos, ' ') << vbar;
+      x_pos = column + 1;
     }
 
     // Print the line connecting the ^ with the error message.
     uint16_t column = detail->source_location->column;
-    if (offset <= column)
-      stream << std::string(column - offset, ' ') << joint << hbar << spacer;
+    if (x_pos <= column)
+      stream << std::string(column - x_pos, ' ') << joint << hbar << spacer;
 
     // Print a colorized string based on the message's severity type.
     PrintSeverity(stream, detail->severity);

lldb/unittests/Utility/DiagnosticsRenderingTest.cpp

@@ -57,4 +57,22 @@ TEST_F(ErrorDisplayTest, RenderStatus) {
                 DiagnosticDetail{loc1, eSeverityError, "Y", "Y"}});
     ASSERT_LT(StringRef(result).find("Y"), StringRef(result).find("X"));
   }
+  {
+    // Test that range diagnostics are emitted correctly.
+    SourceLocation loc1 = {FileSpec{"a.c"}, 1, 1, 3, false, true};
+    SourceLocation loc2 = {FileSpec{"a.c"}, 1, 5, 3, false, true};
+    std::string result =
+        Render({DiagnosticDetail{loc1, eSeverityError, "X", "X"},
+                DiagnosticDetail{loc2, eSeverityError, "Y", "Y"}});
+    auto lines = StringRef(result).split('\n');
+    auto line1 = lines.first;
+    lines = lines.second.split('\n');
+    auto line2 = lines.first;
+    lines = lines.second.split('\n');
+    auto line3 = lines.first;
+    //               1234567
+    ASSERT_EQ(line1, "^~~ ^~~");
+    ASSERT_EQ(line2, "|   error: Y");
+    ASSERT_EQ(line3, "error: X");
+  }
 }