Tiny patch for Go 1.0.3 to turn "is declared and not used" and "imported and not used" errors into warnings. See comment below.

annoying.patch

diff -r 2d8bc3c94ecb src/cmd/gc/lex.c
--- a/src/cmd/gc/lex.c        Fri Sep 21 17:10:44 2012 -0500
+++ b/src/cmd/gc/lex.c	Sat Jan 19 18:25:39 2013 +0400
@@ -2200,7 +2200,7 @@
 					// errors if a conflicting top-level name is
 					// introduced by a different file.
 					if(!s->def->used && !nsyntaxerrors)
-						yyerrorl(s->def->lineno, "imported and not used: \"%Z\"", s->def->pkg->path);
+						warnl(s->def->lineno, "imported and not used: \"%Z\"", s->def->pkg->path);
 					s->def = N;
 					continue;
 				}
@@ -2208,7 +2208,7 @@
 					// throw away top-level name left over
 					// from previous import . "x"
 					if(s->def->pack != N && !s->def->pack->used && !nsyntaxerrors) {
-						yyerrorl(s->def->pack->lineno, "imported and not used: \"%Z\"", s->def->pack->pkg->path);
+						warnl(s->def->pack->lineno, "imported and not used: \"%Z\"", s->def->pack->pkg->path);
 						s->def->pack->used = 1;
 					}
 					s->def = N;
diff -r 2d8bc3c94ecb src/cmd/gc/subr.c
--- a/src/cmd/gc/subr.c	Fri Sep 21 17:10:44 2012 -0500
+++ b/src/cmd/gc/subr.c	Sat Jan 19 18:25:39 2013 +0400
@@ -400,7 +400,7 @@
 	}
 	if(n == 0) {
 		// can't possibly be used - there were no symbols
-		yyerrorl(pack->lineno, "imported and not used: \"%Z\"", opkg->path);
+		warnl(pack->lineno, "imported and not used: \"%Z\"", opkg->path);
 	}
 }
 
diff -r 2d8bc3c94ecb src/cmd/gc/walk.c
--- a/src/cmd/gc/walk.c	Fri Sep 21 17:10:44 2012 -0500
+++ b/src/cmd/gc/walk.c	Sat Jan 19 18:25:39 2013 +0400
@@ -94,11 +94,11 @@
 			if(l->n->defn->left->used)
 				continue;
 			lineno = l->n->defn->left->lineno;
-			yyerror("%S declared and not used", l->n->sym);
+			warn("%S declared and not used", l->n->sym);
 			l->n->defn->left->used = 1; // suppress repeats
 		} else {
 			lineno = l->n->lineno;
-			yyerror("%S declared and not used", l->n->sym);
+			warn("%S declared and not used", l->n->sym);
 		}
 	}	
 

This tiny patch for Go 1.0.3 turns "is declared and not used" and "imported and not used" errors into warnings. Inspired by http://corte.si/posts/code/go/go-rant.html

How to apply it:

curl -O http://go.googlecode.com/files/go1.0.3.src.tar.gz
tar -xf go1.0.3.src.tar.gz
cd go
curl https://gist.github.com/raw/4572944/2ea58f2faeccdb77924904a0ffbed58655ff134f/annoying.patch | patch -p1
cd src
./all.bash

Looks like a good patch. If you're new to Go, however, I'd like to point out the effect of the following changes to the code in cortesi's blog post:

import (
    "io/ioutil"
    "fmt"
)

// BUG: remove this after debugging
// no need to fuss with imports when debugging with fmt
// just put this here:
var _ = fmt.Print

...
...
    m, err := ioutil.ReadFile(path)
    if err != nil {
        return nil, err
    }
...
...
    // no need to hunt for the declaration of m, just put this by the comment:
    _ = m
    //DoSomething(m)

@sethwklein I'm not new to Go, I write Go code for 💰 every day now, and I also created gonuts.io for community. I know how blank identifier works. Generally, I like how Go threats those errors as fatal. But for local hacking it sometimes throws me out of my "zone". I made this patch to actually experience the other side, not just read/write about it.

@AlekSi Of course you're not new to go; most people patching the Go compiler aren't, I think :) Many people reading this may be, though, and might not have read http://golang.org/doc/faq#unused_variables_and_imports. Peace.