Show file and line number of call during errors

This commit makes erroneous calls show their origin. Unexpected calls
show where they happened. Missing calls and improper expectations show
where they were set up in the tests. This information is printed after
each error message in square brackets.

This commit was originally:
ooesili@76f75d8
and a PR for it: golang#25. But there were
minor conflicts with master from 2 aug 2017:
golang@13f3609,
which I fixed.

Author: xmik

gomock/call.go

@@ -29,6 +29,7 @@ type Call struct {
 	methodType reflect.Type  // the type of the method
 	args       []Matcher     // the args
 	rets       []interface{} // the return values (if any)
+	origin     string        // file and line number of call setup
 
 	preReqs []*Call // prerequisite calls
 
@@ -79,8 +80,8 @@ func (c *Call) Do(f interface{}) *Call {
 func (c *Call) Return(rets ...interface{}) *Call {
 	mt := c.methodType
 	if len(rets) != mt.NumOut() {
-		c.t.Fatalf("wrong number of arguments to Return for %T.%v: got %d, want %d",
-			c.receiver, c.method, len(rets), mt.NumOut())
+		c.t.Fatalf("wrong number of arguments to Return for %T.%v: got %d, want %d [%s]",
+			c.receiver, c.method, len(rets), mt.NumOut(), c.origin)
 	}
 	for i, ret := range rets {
 		if got, want := reflect.TypeOf(ret), mt.Out(i); got == want {
@@ -91,8 +92,8 @@ func (c *Call) Return(rets ...interface{}) *Call {
 			case reflect.Chan, reflect.Func, reflect.Interface, reflect.Map, reflect.Ptr, reflect.Slice:
 				// ok
 			default:
-				c.t.Fatalf("argument %d to Return for %T.%v is nil, but %v is not nillable",
-					i, c.receiver, c.method, want)
+				c.t.Fatalf("argument %d to Return for %T.%v is nil, but %v is not nillable [%s]",
+					i, c.receiver, c.method, want, c.origin)
 			}
 		} else if got.AssignableTo(want) {
 			// Assignable type relation. Make the assignment now so that the generated code
@@ -101,8 +102,8 @@ func (c *Call) Return(rets ...interface{}) *Call {
 			v.Set(reflect.ValueOf(ret))
 			rets[i] = v.Interface()
 		} else {
-			c.t.Fatalf("wrong type of argument %d to Return for %T.%v: %v is not assignable to %v",
-				i, c.receiver, c.method, got, want)
+			c.t.Fatalf("wrong type of argument %d to Return for %T.%v: %v is not assignable to %v [%s]",
+				i, c.receiver, c.method, got, want, c.origin)
 		}
 	}
 
@@ -125,7 +126,8 @@ func (c *Call) SetArg(n int, value interface{}) *Call {
 	// TODO: This will break on variadic methods.
 	// We will need to check those at invocation time.
 	if n < 0 || n >= mt.NumIn() {
-		c.t.Fatalf("SetArg(%d, ...) called for a method with %d args", n, mt.NumIn())
+		c.t.Fatalf("SetArg(%d, ...) called for a method with %d args [%s]",
+			n, mt.NumIn(), c.origin)
 	}
 	// Permit setting argument through an interface.
 	// In the interface case, we don't (nay, can't) check the type here.
@@ -134,12 +136,14 @@ func (c *Call) SetArg(n int, value interface{}) *Call {
 	case reflect.Ptr:
 		dt := at.Elem()
 		if vt := reflect.TypeOf(value); !vt.AssignableTo(dt) {
-			c.t.Fatalf("SetArg(%d, ...) argument is a %v, not assignable to %v", n, vt, dt)
+			c.t.Fatalf("SetArg(%d, ...) argument is a %v, not assignable to %v [%s]",
+				n, vt, dt, c.origin)
 		}
 	case reflect.Interface:
 		// nothing to do
 	default:
-		c.t.Fatalf("SetArg(%d, ...) referring to argument of non-pointer non-interface type %v", n, at)
+		c.t.Fatalf("SetArg(%d, ...) referring to argument of non-pointer non-interface type %v [%s]",
+			n, at, c.origin)
 	}
 	c.setArgs[n] = reflect.ValueOf(value)
 	return c
@@ -184,7 +188,7 @@ func (c *Call) String() string {
 		args[i] = arg.String()
 	}
 	arguments := strings.Join(args, ", ")
-	return fmt.Sprintf("%T.%v(%s)", c.receiver, c.method, arguments)
+	return fmt.Sprintf("%T.%v(%s) [%s]", c.receiver, c.method, arguments, c.origin)
 }
 
 // Tests if the given call matches the expected call.

gomock/controller.go

@@ -58,6 +58,7 @@ package gomock
 import (
 	"fmt"
 	"reflect"
+	"runtime"
 	"sync"
 )
 
@@ -114,7 +115,8 @@ func (ctrl *Controller) RecordCallWithMethodType(receiver interface{}, method st
 	ctrl.mu.Lock()
 	defer ctrl.mu.Unlock()
 
-	call := &Call{t: ctrl.t, receiver: receiver, method: method, methodType: methodType, args: margs, minCalls: 1, maxCalls: 1}
+	origin := callerInfo(2)
+	call := &Call{t: ctrl.t, receiver: receiver, method: method, methodType: methodType, args: margs, origin: origin, minCalls: 1, maxCalls: 1}
 
 	ctrl.expectedCalls.Add(call)
 	return call
@@ -126,7 +128,8 @@ func (ctrl *Controller) Call(receiver interface{}, method string, args ...interf
 
 	expected := ctrl.expectedCalls.FindMatch(receiver, method, args)
 	if expected == nil {
-		ctrl.t.Fatalf("no matching expected call: %T.%v(%v)", receiver, method, args)
+		origin := callerInfo(2)
+		ctrl.t.Fatalf("no matching expected call: %T.%v(%v) [%s]", receiver, method, args, origin)
 	}
 
 	// Two things happen here:
@@ -181,3 +184,10 @@ func (ctrl *Controller) Finish() {
 		ctrl.t.Fatalf("aborting test due to missing call(s)")
 	}
 }
+
+func callerInfo(skip int) string {
+	if _, file, line, ok := runtime.Caller(skip + 1); ok {
+		return fmt.Sprintf("%s:%d", file, line)
+	}
+	return "unknown file"
+}