Read code from a file instead of argv[1]

chibicc.h

@@ -1,8 +1,10 @@
 #include <assert.h>
 #include <ctype.h>
+#include <errno.h>
 #include <stdarg.h>
 #include <stdbool.h>
 #include <stdio.h>
+#include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
@@ -48,6 +50,7 @@ bool at_eof();
 Token *new_token(TokenKind kind, Token *cur, char *str, int len);
 Token *tokenize();
 
+extern char *filename;
 extern char *user_input;
 extern Token *token;
 

main.c

@@ -1,5 +1,25 @@
 #include "chibicc.h"
 
+// Returns the contents of a given file.
+char *read_file(char *path) {
+  // Open and read the file.
+  FILE *fp = fopen(path, "r");
+  if (!fp)
+    error("cannot open %s: %s", path, strerror(errno));
+
+  int filemax = 10 * 1024 * 1024;
+  char *buf = malloc(filemax);
+  int size = fread(buf, 1, filemax - 2, fp);
+  if (!feof(fp))
+    error("%s: file too large");
+
+  // Make sure that the string ends with "\n\0".
+  if (size == 0 || buf[size - 1] != '\n')
+    buf[size++] = '\n';
+  buf[size] = '\0';
+  return buf;
+}
+
 int align_to(int n, int align) {
   return (n + align - 1) & ~(align - 1);
 }
@@ -9,7 +29,8 @@ int main(int argc, char **argv) {
     error("%s: invalid number of arguments", argv[0]);
 
   // Tokenize and parse.
-  user_input = argv[1];
+  filename = argv[1];
+  user_input = read_file(argv[1]);
   token = tokenize();
   Program *prog = program();
   add_type(prog);

test.sh

@@ -14,7 +14,7 @@ assert() {
   expected="$1"
   input="$2"
 
-  ./chibicc "$input" > tmp.s
+  ./chibicc <(echo "$input") > tmp.s
   gcc -static -o tmp tmp.s tmp2.o
   ./tmp
   actual="$?"

tokenize.c

@@ -1,5 +1,6 @@
 #include "chibicc.h"
 
+char *filename;
 char *user_input;
 Token *token;
 
@@ -12,10 +13,32 @@ void error(char *fmt, ...) {
   exit(1);
 }
 
-// Reports an error location and exit.
+// Reports an error message in the following format and exit.
+//
+// foo.c:10: x = y + 1;
+//               ^ <error message here>
 void verror_at(char *loc, char *fmt, va_list ap) {
-  int pos = loc - user_input;
-  fprintf(stderr, "%s\n", user_input);
+  // Find a line containing `loc`.
+  char *line = loc;
+  while (user_input < line && line[-1] != '\n')
+    line--;
+
+  char *end = loc;
+  while (*end != '\n')
+    end++;
+
+  // Get a line number.
+  int line_num = 1;
+  for (char *p = user_input; p < line; p++)
+    if (*p == '\n')
+      line_num++;
+
+  // Print out the line.
+  int indent = fprintf(stderr, "%s:%d: ", filename, line_num);
+  fprintf(stderr, "%.*s\n", (int)(end - line), line);
+
+  // Show the error message.
+  int pos = loc - line + indent;
   fprintf(stderr, "%*s", pos, ""); // print pos spaces.
   fprintf(stderr, "^ ");
   vfprintf(stderr, fmt, ap);