dsl: add experimental Do() action

Unlike `Report()` and `Suggest()`, new `Do()` method allows
a more granular match action handling.

Now it's possible to emit a conditional report/suggest message
based on the matching context.

The API is experimental and is likely to change.

Author: quasilyte

dsl/do.go

@@ -0,0 +1,19 @@
+package dsl
+
+import (
+	"github.com/quasilyte/go-ruleguard/dsl/types"
+)
+
+type DoContext struct{}
+
+func (*DoContext) Var(varname string) *DoVar { return nil }
+
+func (*DoContext) SetReport(report string) {}
+
+func (*DoContext) SetSuggest(suggest string) {}
+
+type DoVar struct{}
+
+func (*DoVar) Text() string { return "" }
+
+func (*DoVar) Type() types.Type { return nil }

dsl/dsl.go

@@ -78,6 +78,10 @@ func (m Matcher) Suggest(suggestion string) Matcher {
 	return m
 }
 
+func (m Matcher) Do(fn func(*DoContext)) Matcher {
+	return m
+}
+
 // At binds the reported node to a named submatch.
 // If no explicit location is given, the outermost node ($$) is used.
 func (m Matcher) At(v Var) Matcher {