vet: add suggestions for function documentation (#7890)

cmd/tools/vvet/tests/array_init_one_val.out

@@ -1,2 +1,2 @@
-cmd/tools/vvet/tests/array_init_one_val.vv:2: Use `var == value` instead of `var in [value]`
+cmd/tools/vvet/tests/array_init_one_val.vv:2: error: Use `var == value` instead of `var in [value]`
 NB: You can run `v fmt -w file.v` to fix these automatically

cmd/tools/vvet/tests/indent_with_space.out

@@ -1,2 +1,2 @@
-cmd/tools/vvet/tests/indent_with_space.vv:2: Looks like you are using spaces for indentation.
+cmd/tools/vvet/tests/indent_with_space.vv:2: error: Looks like you are using spaces for indentation.
 NB: You can run `v fmt -w file.v` to fix these automatically

cmd/tools/vvet/tests/module_file_test.out

@@ -0,0 +1,4 @@
+cmd/tools/vvet/tests/module_file_test.vv:7: warning: Function documentation seems to be missing for "pub fn foo() string".
+cmd/tools/vvet/tests/module_file_test.vv:13: warning: A function name is missing from the documentation of "pub fn bar() string".
+cmd/tools/vvet/tests/module_file_test.vv:35: warning: Function documentation seems to be missing for "pub fn (f Foo) foo() string".
+cmd/tools/vvet/tests/module_file_test.vv:46: warning: A function name is missing from the documentation of "pub fn (f Foo) fooo() string".

cmd/tools/vvet/tests/module_file_test.vv

@@ -0,0 +1,49 @@
+module foo
+
+struct Foo {
+	foo int
+}
+
+pub fn foo() string {
+	// Missing doc
+	return 'foo'
+}
+
+// foo does bar
+pub fn bar() string {
+	// not using convention style: '// <fn name>'
+	return 'bar'
+}
+
+// fooo does x
+pub fn fooo() string {
+	// Documented
+	return 'fooo'
+}
+
+// booo does x
+fn booo() string {
+	// Documented, but not pub
+	return 'booo'
+}
+
+fn boo() string {
+	// Missing doc
+	return 'boo'
+}
+
+pub fn (f Foo) foo() string {
+	// Missing doc
+	return f.fo()
+}
+
+fn (f Foo) fo() string {
+	// Missing doc, but not pub
+	return 'foo'
+}
+
+// wrong doc
+pub fn (f Foo) fooo() string {
+	// not using convention
+	return f.fo()
+}

cmd/tools/vvet/tests/parens_space_a.out

@@ -1,2 +1,2 @@
-cmd/tools/vvet/tests/parens_space_a.vv:1: Looks like you are adding a space after `(`
+cmd/tools/vvet/tests/parens_space_a.vv:1: error: Looks like you are adding a space after `(`
 NB: You can run `v fmt -w file.v` to fix these automatically

cmd/tools/vvet/tests/parens_space_b.out

@@ -1,2 +1,2 @@
-cmd/tools/vvet/tests/parens_space_b.vv:1: Looks like you are adding a space before `)`
+cmd/tools/vvet/tests/parens_space_b.vv:1: error: Looks like you are adding a space before `)`
 NB: You can run `v fmt -w file.v` to fix these automatically