5 files changed, 36 insertions, 7 deletions

diff --git a/src/cli.c b/src/cli.c
index 7388370..9b62614 100644
--- a/src/cli.c
+++ b/src/cli.c
@@ -14,6 +14,8 @@ CliArgs* parse_cli_args(int argc, char** argv) {
     bool opt_c = false;
     bool opt_E = false;
     bool opt_MMD = false;
+    StrArray include_dirs;
+    strings_init(&include_dirs);
 
     for (int i = 1; i < argc; ++i) {
         if (argv[i][0] != '-') {
@@ -29,6 +31,19 @@ CliArgs* parse_cli_args(int argc, char** argv) {
             // ignore
         } else if (c == 'M' && argv[i][2] == '\0') {
             // ignore -M
+        } else if (c == 'I') {
+            const char* dir = NULL;
+            if (argv[i][2] != '\0') {
+                // -Ipath format
+                dir = argv[i] + 2;
+            } else if (argc > i + 1) {
+                // -I path format
+                dir = argv[i + 1];
+                ++i;
+            } else {
+                fatal_error("-I requires directory");
+            }
+            strings_push(&include_dirs, dir);
         } else if (c == 'o') {
             if (argc <= i + 1) {
                 fatal_error("-o requires filename");
@@ -63,6 +78,7 @@ CliArgs* parse_cli_args(int argc, char** argv) {
     a->totally_deligate_to_gcc = false;
     a->gcc_command = NULL;
     a->generate_deps = opt_MMD;
+    a->include_dirs = include_dirs;
 
     if (!a->only_compile && str_ends_with(a->input_filename, ".o")) {
         a->totally_deligate_to_gcc = true;
diff --git a/src/cli.h b/src/cli.h
index 3b1e7f5..51263e2 100644
--- a/src/cli.h
+++ b/src/cli.h
@@ -1,6 +1,7 @@
 #ifndef DUCC_CLI_H
 #define DUCC_CLI_H
 
+#include "common.h"
 #include "std.h"
 
 typedef struct {
@@ -12,6 +13,7 @@ typedef struct {
     bool generate_deps;
     bool totally_deligate_to_gcc;
     const char* gcc_command;
+    StrArray include_dirs;
 } CliArgs;
 
 CliArgs* parse_cli_args(int argc, char** argv);
diff --git a/src/main.c b/src/main.c
index 469e5db..bd1391c 100644
--- a/src/main.c
+++ b/src/main.c
@@ -22,7 +22,7 @@ int main(int argc, char** argv) {
     StrArray included_files;
     strings_init(&included_files);
 
-    TokenArray* pp_tokens = preprocess(source, &included_files);
+    TokenArray* pp_tokens = preprocess(source, &included_files, &cli_args->include_dirs);
 
     if (cli_args->preprocess_only) {
         FILE* output_file = cli_args->output_filename ? fopen(cli_args->output_filename, "w") : stdout;
diff --git a/src/preprocess.c b/src/preprocess.c
index 5e029f2..00b01dd 100644
--- a/src/preprocess.c
+++ b/src/preprocess.c
@@ -562,7 +562,8 @@ typedef struct {
     StrArray* included_files;
 } Preprocessor;
 
-static TokenArray* do_preprocess(InFile* src, int depth, MacroArray* macros, StrArray* included_files);
+static TokenArray* do_preprocess(InFile* src, int depth, MacroArray* macros, StrArray* included_files,
+                                 StrArray* user_include_dirs);
 
 static Preprocessor* preprocessor_new(TokenArray* pp_tokens, int include_depth, MacroArray* macros,
                                       StrArray* included_files) {
@@ -744,7 +745,7 @@ static void expand_include_directive(Preprocessor* pp, const char* include_name,
     }
 
     TokenArray* include_pp_tokens =
-        do_preprocess(include_source, pp->include_depth + 1, pp->macros, pp->included_files);
+        do_preprocess(include_source, pp->include_depth + 1, pp->macros, pp->included_files, NULL);
     tokens_pop(include_pp_tokens); // pop EOF token
     pp->pos = insert_pp_tokens(pp, pp->pos, include_pp_tokens);
 }
@@ -1541,23 +1542,33 @@ static char* get_ducc_include_path() {
     return buf;
 }
 
-static TokenArray* do_preprocess(InFile* src, int depth, MacroArray* macros, StrArray* included_files) {
+static TokenArray* do_preprocess(InFile* src, int depth, MacroArray* macros, StrArray* included_files,
+                                 StrArray* user_include_dirs) {
     TokenArray* pp_tokens = pp_tokenize(src);
     Preprocessor* pp = preprocessor_new(pp_tokens, depth, macros, included_files);
+
+    // Ducc's built-in headers has highest priority.
     add_include_path(pp, get_ducc_include_path());
+
+    if (user_include_dirs) {
+        for (size_t i = 0; i < user_include_dirs->len; ++i) {
+            add_include_path(pp, user_include_dirs->data[i]);
+        }
+    }
     add_include_path(pp, "/usr/local/include");
     add_include_path(pp, "/usr/include/x86_64-linux-gnu");
     add_include_path(pp, "/usr/include");
+
     preprocess_preprocessing_file(pp);
     remove_pp_directives(pp);
     return pp->pp_tokens;
 }
 
-TokenArray* preprocess(InFile* src, StrArray* included_files) {
+TokenArray* preprocess(InFile* src, StrArray* included_files, StrArray* user_include_dirs) {
     MacroArray* macros = macros_new();
     add_predefined_macros(macros);
     strings_push(included_files, src->loc.filename);
-    return do_preprocess(src, 0, macros, included_files);
+    return do_preprocess(src, 0, macros, included_files, user_include_dirs);
 }
 
 void print_token_to_file(FILE* out, TokenArray* pp_tokens) {
diff --git a/src/preprocess.h b/src/preprocess.h
index 5449857..e78776f 100644
--- a/src/preprocess.h
+++ b/src/preprocess.h
@@ -6,7 +6,7 @@
 #include "io.h"
 #include "token.h"
 
-TokenArray* preprocess(InFile* src, StrArray* included_files);
+TokenArray* preprocess(InFile* src, StrArray* included_files, StrArray* user_include_dirs);
 void print_token_to_file(FILE* output_file, TokenArray* pp_tokens);
 
 #endif