first commit for dfa messagestyle

Author: Iskaban10

compiler/src/dmd/cli.d

@@ -901,14 +901,15 @@ dmd -cov -unittest myprog.d
         Option("vcolumns",
             "print character (column) numbers in diagnostics"
         ),
-        Option("verror-style=[digitalmars|gnu|sarif]",
+        Option("verror-style=[digitalmars|gnu|sarif|dfa]",
             "set the style for file/line number annotations on compiler messages",
             `Set the style for file/line number annotations on compiler messages,
             where:
             $(DL
             $(DT digitalmars)$(DD 'file(line[,column]): message'. This is the default.)
             $(DT gnu)$(DD 'file:line[:column]: message', conforming to the GNU standard used by gcc and clang.)
             $(DT sarif)$(DD 'Generates JSON output conforming to the SARIF (Static Analysis Results Interchange Format) standard, useful for integration with tools like GitHub and other SARIF readers.')
+            $(DT dfa)$(DD 'DFA messagestyle under construction.')
             )`,
         ),
         Option("verror-supplements=<num>",

compiler/src/dmd/diagreport/defs.d

@@ -0,0 +1,59 @@
+module dmd.diagreport.defs;
+
+/**
+    Defines the vertical state of a diagnostic on a given line for drawing purposes.
+    This enumeration captures the vertical state machine logic for a single diagnostic span.
+*/
+enum LineClassification
+{
+    /// The line is not part of the diagnostic span.
+    Inactive,
+    /// The line is the start of the span and continues below. Implies the previous line was Inactive.
+    SpanStart,
+    /// The line is between the start and end. Implies the previous line and next line are Active.
+    SpanContinue,
+    /// The line is the end of the span and no other active diagnostics follow it. Implies the next line is Inactive.
+    SpanEnd,
+    /// The span starts and ends on the same line (a one-line diagnostic).
+    SpanStartEnd
+}
+
+struct Diagnostic
+{
+    /// The line number where the diagnostic span begins (inclusive).
+    int start;
+    /// The line number where the diagnostic span ends (inclusive).
+    int end;
+
+    Message startMessage;
+    Message endMessage;
+
+    size_t id;
+
+    size_t offset()
+    {
+        return originalOffset;
+    }
+
+package:
+    size_t originalOffset;
+    int column;
+}
+
+struct Message
+{
+    int startColumn, endColumn;
+    bool isMultiline;
+
+    size_t id;
+}
+
+struct Help
+{
+    Diagnostic[] diagnostics;
+
+    Message startMessage;
+    Message endMessage;
+
+    size_t id;
+}