checker,cgen: support -d trace_check and -d trace_cgen to help diagnose checker and cgen ordering issues

Author: spytheman

CONTRIBUTING.md

@@ -325,12 +325,14 @@ a copy of the compiler rather than replacing it with `v self`.
 | `trace_scanner`                   | Prints details about the recognized tokens. *Very* verbose. Use with `./vnew -no-builtin -check-syntax file.v` .    |
 | `trace_parse`                     | Prints details about the parsed files (number of tokens, lines, bytes). Use it for parsing order issues.            |
 | `trace_parser`                    | Prints details about parsed statements and expressions. Very verbose. Use it for panics in the parser.              |
+| `trace_check`                     | Prints the .v file which is checked. Use it to diagnose checker order issues.                                       |
 | `trace_checker`                   | Prints details about the statements being checked. Very verbose. Use it for panics in the checker.                  |
 | `trace_transformer`               | Prints details about the statements being transformed. Very verbose. Use it for panics in the transformer stage.    |
 |                                   |                                                                                                                     |
 | `trace_gen`                       | Prints all the strings written to the generated C file. Very verbose.                                               |
 | `trace_gen_wanted_value`          | Prints a backtrace, when a specific *wanted* value, is part of what is printed in the generated C file.             |
 |                                   |        Use: `v -g -o vgen -d trace_gen_wanted -d trace_gen_wanted_value="message = _SLIT0" cmd/v && ./vgen bug.v`   |
+| `trace_cgen`                      | Prints the .v file for which C code generation runs. Use it to diagnose cgen order issues.                          |
 | `trace_cgen_stmt`                 | Prints details about the statements that are being processed by cgen.                                               |
 |                                   |        Use it for panics in cgen, to see the closest input V source line, that caused the panic.                    |
 |                                   |        Note: you need `v -no-parallel -d trace_cgen_stmt -o w cmd/v` to make sense of the output of that,           |

vlib/v/checker/checker.v

@@ -218,6 +218,9 @@ fn (mut c Checker) reset_checker_state_at_start_of_new_file() {
 }
 
 pub fn (mut c Checker) check(mut ast_file ast.File) {
+	$if trace_check ? {
+		eprintln('> ${@FILE}:${@LINE} | ast_file.path: ${ast_file.path}')
+	}
 	$if trace_checker ? {
 		eprintln('start checking file: ${ast_file.path}')
 	}

vlib/v/gen/c/cgen.v

@@ -924,6 +924,9 @@ pub fn (mut g Gen) free_builders() {
 }
 
 pub fn (mut g Gen) gen_file() {
+	$if trace_cgen ? {
+		eprintln('> ${@FILE}:${@LINE} | g.file.path: ${g.file.path}')
+	}
 	g.timers.start('cgen_file ${g.file.path}')
 	g.unique_file_path_hash = fnv1a.sum64_string(g.file.path)
 	if g.pref.is_vlines {