cmd/doc: stop showing interface methods while matching symbols

Fixes golang#31961

Change-Id: I9db9ecfd2f8ca7cf51df4413a6e0d66de5da7043
Reviewed-on: https://go-review.googlesource.com/c/go/+/178457
Run-TryBot: Agniva De Sarker <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Rob Pike <[email protected]>

src/cmd/doc/doc_test.go

@@ -602,6 +602,19 @@ var tests = []test{
 			`Comment about exported interface`,
 		},
 	},
+	// Interface method at package level.
+	{
+		"interface method at package level",
+		[]string{p, `ExportedMethod`},
+		[]string{
+			`func \(ExportedType\) ExportedMethod\(a int\) bool`,
+			`Comment about exported method`,
+		},
+		[]string{
+			`Comment before exported method.*\n.*ExportedMethod\(\)` +
+				`.*Comment on line with exported method`,
+		},
+	},
 
 	// Method.
 	{

src/cmd/doc/pkg.go

@@ -914,8 +914,8 @@ func trimUnexportedFields(fields *ast.FieldList, isInterface bool) *ast.FieldLis
 }
 
 // printMethodDoc prints the docs for matches of symbol.method.
-// If symbol is empty, it prints all methods that match the name.
-// It reports whether it found any methods.
+// If symbol is empty, it prints all methods for any concrete type
+// that match the name. It reports whether it found any methods.
 func (pkg *Package) printMethodDoc(symbol, method string) bool {
 	defer pkg.flush()
 	types := pkg.findTypes(symbol)
@@ -937,6 +937,9 @@ func (pkg *Package) printMethodDoc(symbol, method string) bool {
 			}
 			continue
 		}
+		if symbol == "" {
+			continue
+		}
 		// Type may be an interface. The go/doc package does not attach
 		// an interface's methods to the doc.Type. We need to dig around.
 		spec := pkg.findTypeSpec(typ.Decl, typ.Name)