Add syntax error for signed line numbers

Author: glankk

simplecpp.cpp

@@ -737,6 +737,19 @@ void simplecpp::TokenList::readfile(Stream &stream, const std::string &filename,
                 if (ppTok->str() == "line")
                     ppTok = advanceAndSkipComments(ppTok);
 
+                if (ppTok && (ppTok->str()[0] == '-' || ppTok->str()[0] == '+')) {
+                    if (outputList) {
+                        simplecpp::Output err{
+                            simplecpp::Output::SYNTAX_ERROR,
+                            location,
+                            "Invalid character in line directive: '" + ppTok->str() + "'."
+                        };
+                        outputList->emplace_back(std::move(err));
+                    }
+                    clear();
+                    return;
+                }
+
                 if (!ppTok || !ppTok->number)
                     continue;
 

test.cpp

@@ -2869,6 +2869,16 @@ static void lineDirective()
         simplecpp::DUI dui;
         dui.std = std;
 
+        {
+            const char code[] =
+                "#line -1\n"
+                ";\n";
+            simplecpp::OutputList outputList;
+            makeTokenList(code, dui, &outputList);
+            ASSERT_EQUALS("file0,2,syntax_error,Invalid character in line directive: '-'.\n",
+                          toString(outputList));
+        }
+
         {
             const char code[] =
                 "#line 0\n"
@@ -2919,6 +2929,16 @@ static void lineDirective()
         simplecpp::DUI dui;
         dui.std = std;
 
+        {
+            const char code[] =
+                "#line -1\n"
+                ";\n";
+            simplecpp::OutputList outputList;
+            makeTokenList(code, dui, &outputList);
+            ASSERT_EQUALS("file0,2,syntax_error,Invalid character in line directive: '-'.\n",
+                          toString(outputList));
+        }
+
         {
             const char code[] =
                 "#line 0\n"
@@ -2983,6 +3003,16 @@ static void lineDirective()
         simplecpp::DUI dui;
         dui.std = "c++26";
 
+        {
+            const char code[] =
+                "#line -1\n"
+                ";\n";
+            simplecpp::OutputList outputList;
+            makeTokenList(code, dui, &outputList);
+            ASSERT_EQUALS("file0,2,syntax_error,Invalid character in line directive: '-'.\n",
+                          toString(outputList));
+        }
+
         {
             const char code[] =
                 "#line 0\n"