From 8b991b158417aa21f0b0d8fa87af53df90272744 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@vlang.io>
Date: Fri, 8 Nov 2024 11:59:31 +0300
Subject: [PATCH] checker: auto generate missing C function definitions

---
 vlib/v/checker/fn.v                           | 30 +++++++++++++++++++
 .../tests/include_c_gen_fn_headers/cheader.h  |  9 ++++++
 .../include_c_gen_fn_headers/include_c.v      | 16 ++++++++++
 3 files changed, 55 insertions(+)
 create mode 100644 vlib/v/tests/include_c_gen_fn_headers/cheader.h
 create mode 100644 vlib/v/tests/include_c_gen_fn_headers/include_c.v

diff --git a/vlib/v/checker/fn.v b/vlib/v/checker/fn.v
index 1095acb02..184ae85f6 100644
--- a/vlib/v/checker/fn.v
+++ b/vlib/v/checker/fn.v
@@ -4,6 +4,7 @@ import strings
 import v.ast
 import v.util
 import v.token
+import os
 
 const print_everything_fns = ['println', 'print', 'eprintln', 'eprint', 'panic']
 
@@ -1265,6 +1266,35 @@ fn (mut c Checker) fn_call(mut node ast.CallExpr, mut continue_check &bool) ast.
 				return ast.void_type
 			}
 		}
+		name := node.get_name()
+		if name.starts_with('C.') {
+			println('unknown function ${name}, ' +
+				'searching for the C definition in one of the #includes')
+			mut includes := []string{cap: 5}
+			for stmt in c.file.stmts {
+				if stmt is ast.HashStmt {
+					if stmt.kind == 'include' {
+						includes << '#include ${stmt.main}'
+					}
+				}
+			}
+			mut tmp_c_file_with_includes := os.create('tmp.c') or { panic(err) }
+			tmp_c_file_with_includes.write_string(includes.join('\n')) or { panic(err) }
+			tmp_c_file_with_includes.close()
+
+			os.execute('v translate fndef ${name[2..]} tmp.c')
+			x := os.read_file('__cdefs_autogen.v') or { return ast.void_type }
+			if x.contains('fn ${name}') {
+				println(
+					'function definition for ${name} has been generated in __cdefs_autogen.v. ' +
+					'Please re-run the compilation with `v .` or `v run .`')
+				os.rm('tmp.c') or {}
+				exit(0)
+			} else {
+				println('Failed to generate function definition. Please report it via github.com/vlang/v/issues')
+			}
+			os.rm('tmp.c') or {}
+		}
 		c.error('unknown function: ${node.get_name()}', node.pos)
 		return ast.void_type
 	}
diff --git a/vlib/v/tests/include_c_gen_fn_headers/cheader.h b/vlib/v/tests/include_c_gen_fn_headers/cheader.h
new file mode 100644
index 000000000..e89cc5a21
--- /dev/null
+++ b/vlib/v/tests/include_c_gen_fn_headers/cheader.h
@@ -0,0 +1,9 @@
+#include <stdio.h>
+
+void hello_from_c() {
+	puts("Hello from C!");
+}
+
+int add_two_numbers(int a, int b) {
+	return a + b;
+}
diff --git a/vlib/v/tests/include_c_gen_fn_headers/include_c.v b/vlib/v/tests/include_c_gen_fn_headers/include_c.v
new file mode 100644
index 000000000..ae0eac14f
--- /dev/null
+++ b/vlib/v/tests/include_c_gen_fn_headers/include_c.v
@@ -0,0 +1,16 @@
+#flag -I.
+#include "cheader.h"
+
+// fn C.hello_from_c()
+
+// fn C.add_two_numbers(a int, b int) int
+
+fn test_include_c_autogen_of_fn_definitions() {
+	C.hello_from_c()
+	x := C.add_two_numbers(2, 3)
+	assert x == 5
+}
+
+fn main() {
+	test_include_c_autogen_of_fn_definitions()
+}
-- 
2.39.5