feat: warn when it looks like you're using ignore instead of exclude …

…directive (#1955)

**What type of PR is this?**

Feature

**What package or component does this PR mostly affect?**

all

**What does this PR do? Why is it needed?**

`ignore` and `exclude` are somewhat confusing directive names, and are
easily mixed up. Show a warning when using the `gazelle:ignore`
directive with an argument.

I've seen many places where people do something like `# gazelle:ignore
testdata` and accidentally disable gazelle for the entire directory and
subdirectories. This can be seen in [many public github
repos](https://github.com/search?q=%2F%23+gazelle%3Aignore+.%2F+language%3AStarlark&type=code&l=Starlark).

**Other notes for review**

Add a new generated test directory to assert that the warning is shown
correctly.

tests/warns_on_invalid_directive_use/README.md

@@ -0,0 +1 @@
+# Gazelle warns on invalid directive use

tests/warns_on_invalid_directive_use/arguments.txt

@@ -0,0 +1,2 @@
+-lang
+nolang

tests/warns_on_invalid_directive_use/expectedExitCode.txt

@@ -0,0 +1 @@
+0

tests/warns_on_invalid_directive_use/expectedStderr.txt

@@ -0,0 +1 @@
+gazelle: the ignore directive does not take any arguments. Did you mean to use gazelle:exclude instead? in //ignore_directive '# gazelle:ignore *.go'

tests/warns_on_invalid_directive_use/ignore_directive/BUILD.in

@@ -0,0 +1,4 @@
+# gazelle:ignore *.go
+
+# valid use, but trailing whitespace should not warn
+# gazelle:ignore    

tests/warns_on_invalid_directive_use/ignore_directive/BUILD.out

@@ -0,0 +1,4 @@
+# gazelle:ignore *.go
+
+# valid use, but trailing whitespace should not warn
+# gazelle:ignore    

walk/config.go

@@ -95,6 +95,9 @@ func (cr *Configurer) Configure(c *config.Config, rel string, f *rule.File) {
 				}
 				wcCopy.follow = append(wcCopy.follow, path.Join(rel, d.Value))
 			case "ignore":
+				if d.Value != "" {
+					log.Printf("the ignore directive does not take any arguments. Did you mean to use gazelle:exclude instead? in //%s '# gazelle:ignore %s'", f.Pkg, d.Value)
+				}
 				wcCopy.ignore = true
 			}
 		}