From 3cd2d96611dca718ae7fd24ea227059fdd12e2cd Mon Sep 17 00:00:00 2001
From: Josh Holtrop <jholtrop@gmail.com>
Date: Mon, 23 Apr 2018 23:51:35 -0400
Subject: [PATCH] Display original source file location for errors

---
 src/parser/parser.c | 87 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 87 insertions(+)

diff --git a/src/parser/parser.c b/src/parser/parser.c
index 5eb6213..b38fb0c 100644
--- a/src/parser/parser.c
+++ b/src/parser/parser.c
@@ -4,6 +4,7 @@
 #include <sys/stat.h>
 #include <fcntl.h>
 #include <unistd.h>
+#include <stdbool.h>
 
 extern FILE * yyin;
 
@@ -59,6 +60,80 @@ static char * read_file(const char * filename, size_t * length)
     return buf;
 }
 
+int orig_line = -1;
+const char * orig_file = NULL;
+
+static void scan_source_line_for_orig_location(char * source_line, int max_length)
+{
+    int state = 0;
+    char * orig_file_build = NULL;
+    for (int i = 0;
+         (i < max_length) && (source_line[i] != '\n');
+         i++)
+    {
+        char c = source_line[i];
+        switch (state)
+        {
+        case 0:
+            if (c == '#')
+            {
+                state++;
+            }
+            else if (c != ' ')
+            {
+                return;
+            }
+            break;
+        case 1:
+            if (('0' <= c) && (c <= '9'))
+            {
+                orig_line = c - '0';
+                state++;
+            }
+            else if (c != ' ')
+            {
+                return;
+            }
+            break;
+        case 2:
+            if (('0' <= c) && (c <= '9'))
+            {
+                orig_line *= 10;
+                orig_line += c - '0';
+            }
+            else if (c == ' ')
+            {
+                state++;
+            }
+            else
+            {
+                return;
+            }
+            break;
+        case 3:
+            if (c == '"')
+            {
+                orig_line--;
+                orig_file_build = &source_line[i + 1];
+                state++;
+            }
+            else if (c != ' ')
+            {
+                return;
+            }
+            break;
+        case 4:
+            if (c == '"')
+            {
+                source_line[i] = '\0';
+                orig_file = orig_file_build;
+                return;
+            }
+            break;
+        }
+    }
+}
+
 static void display_error_source(int line, int column)
 {
     if (line < 0)
@@ -72,6 +147,7 @@ static void display_error_source(int line, int column)
 
     int search_line = 1;
     const char * line_begin = NULL;
+    bool scan_for_location = true;
     for (size_t i = 0u; i < length; i++)
     {
         if (search_line == line)
@@ -79,6 +155,11 @@ static void display_error_source(int line, int column)
             line_begin = &file[i];
             search_line++;
         }
+        if (scan_for_location)
+        {
+            scan_source_line_for_orig_location(&file[i], length - i);
+            scan_for_location = false;
+        }
         if (file[i] == '\n')
         {
             if (line_begin != NULL)
@@ -90,9 +171,15 @@ static void display_error_source(int line, int column)
                     fprintf(stderr, " ");
                 }
                 fprintf(stderr, "^\n");
+                if (orig_file != NULL)
+                {
+                    fprintf(stderr, "Originally from %s:%d\n", orig_file, orig_line);
+                }
                 break;
             }
             search_line++;
+            orig_line++;
+            scan_for_location = true;
         }
     }
 }