Merge pull request stretchr#1615 from DevotedHealth/mauclair-mock-match-sprintf

Lazily render mock diff output on successful match

Author: brackendawson

mock/mock.go

@@ -948,56 +948,75 @@ func (args Arguments) Is(objects ...interface{}) bool {
 	return true
 }
 
+type outputRenderer func() string
+
 // Diff gets a string describing the differences between the arguments
 // and the specified objects.
 //
 // Returns the diff string and number of differences found.
 func (args Arguments) Diff(objects []interface{}) (string, int) {
 	// TODO: could return string as error and nil for No difference
 
-	output := "\n"
+	var outputBuilder strings.Builder
 	var differences int
 
 	maxArgCount := len(args)
 	if len(objects) > maxArgCount {
 		maxArgCount = len(objects)
 	}
 
+	outputRenderers := []outputRenderer{}
+
 	for i := 0; i < maxArgCount; i++ {
+		i := i
 		var actual, expected interface{}
-		var actualFmt, expectedFmt string
+		var actualFmt, expectedFmt func() string
 
 		if len(objects) <= i {
 			actual = "(Missing)"
-			actualFmt = "(Missing)"
+			actualFmt = func() string {
+				return "(Missing)"
+			}
 		} else {
 			actual = objects[i]
-			actualFmt = fmt.Sprintf("(%[1]T=%[1]v)", actual)
+			actualFmt = func() string {
+				return fmt.Sprintf("(%[1]T=%[1]v)", actual)
+			}
 		}
 
 		if len(args) <= i {
 			expected = "(Missing)"
-			expectedFmt = "(Missing)"
+			expectedFmt = func() string {
+				return "(Missing)"
+			}
 		} else {
 			expected = args[i]
-			expectedFmt = fmt.Sprintf("(%[1]T=%[1]v)", expected)
+			expectedFmt = func() string {
+				return fmt.Sprintf("(%[1]T=%[1]v)", expected)
+			}
 		}
 
 		if matcher, ok := expected.(argumentMatcher); ok {
 			var matches bool
 			func() {
 				defer func() {
 					if r := recover(); r != nil {
-						actualFmt = fmt.Sprintf("panic in argument matcher: %v", r)
+						actualFmt = func() string {
+							return fmt.Sprintf("panic in argument matcher: %v", r)
+						}
 					}
 				}()
 				matches = matcher.Matches(actual)
 			}()
 			if matches {
-				output = fmt.Sprintf("%s\t%d: PASS:  %s matched by %s\n", output, i, actualFmt, matcher)
+				outputRenderers = append(outputRenderers, func() string {
+					return fmt.Sprintf("\t%d: PASS:  %s matched by %s\n", i, actualFmt(), matcher)
+				})
 			} else {
 				differences++
-				output = fmt.Sprintf("%s\t%d: FAIL:  %s not matched by %s\n", output, i, actualFmt, matcher)
+				outputRenderers = append(outputRenderers, func() string {
+					return fmt.Sprintf("\t%d: FAIL:  %s not matched by %s\n", i, actualFmt(), matcher)
+				})
 			}
 		} else {
 			switch expected := expected.(type) {
@@ -1006,13 +1025,17 @@ func (args Arguments) Diff(objects []interface{}) (string, int) {
 				if reflect.TypeOf(actual).Name() != string(expected) && reflect.TypeOf(actual).String() != string(expected) {
 					// not match
 					differences++
-					output = fmt.Sprintf("%s\t%d: FAIL:  type %s != type %s - %s\n", output, i, expected, reflect.TypeOf(actual).Name(), actualFmt)
+					outputRenderers = append(outputRenderers, func() string {
+						return fmt.Sprintf("\t%d: FAIL:  type %s != type %s - %s\n", i, expected, reflect.TypeOf(actual).Name(), actualFmt())
+					})
 				}
 			case *IsTypeArgument:
 				actualT := reflect.TypeOf(actual)
 				if actualT != expected.t {
 					differences++
-					output = fmt.Sprintf("%s\t%d: FAIL:  type %s != type %s - %s\n", output, i, expected.t.Name(), actualT.Name(), actualFmt)
+					outputRenderers = append(outputRenderers, func() string {
+						return fmt.Sprintf("\t%d: FAIL:  type %s != type %s - %s\n", i, expected.t.Name(), actualT.Name(), actualFmt())
+					})
 				}
 			case *FunctionalOptionsArgument:
 				var name string
@@ -1023,26 +1046,36 @@ func (args Arguments) Diff(objects []interface{}) (string, int) {
 				const tName = "[]interface{}"
 				if name != reflect.TypeOf(actual).String() && len(expected.values) != 0 {
 					differences++
-					output = fmt.Sprintf("%s\t%d: FAIL:  type %s != type %s - %s\n", output, i, tName, reflect.TypeOf(actual).Name(), actualFmt)
+					outputRenderers = append(outputRenderers, func() string {
+						return fmt.Sprintf("\t%d: FAIL:  type %s != type %s - %s\n", i, tName, reflect.TypeOf(actual).Name(), actualFmt())
+					})
 				} else {
 					if ef, af := assertOpts(expected.values, actual); ef == "" && af == "" {
 						// match
-						output = fmt.Sprintf("%s\t%d: PASS:  %s == %s\n", output, i, tName, tName)
+						outputRenderers = append(outputRenderers, func() string {
+							return fmt.Sprintf("\t%d: PASS:  %s == %s\n", i, tName, tName)
+						})
 					} else {
 						// not match
 						differences++
-						output = fmt.Sprintf("%s\t%d: FAIL:  %s != %s\n", output, i, af, ef)
+						outputRenderers = append(outputRenderers, func() string {
+							return fmt.Sprintf("\t%d: FAIL:  %s != %s\n", i, af, ef)
+						})
 					}
 				}
 
 			default:
 				if assert.ObjectsAreEqual(expected, Anything) || assert.ObjectsAreEqual(actual, Anything) || assert.ObjectsAreEqual(actual, expected) {
 					// match
-					output = fmt.Sprintf("%s\t%d: PASS:  %s == %s\n", output, i, actualFmt, expectedFmt)
+					outputRenderers = append(outputRenderers, func() string {
+						return fmt.Sprintf("\t%d: PASS:  %s == %s\n", i, actualFmt(), expectedFmt())
+					})
 				} else {
 					// not match
 					differences++
-					output = fmt.Sprintf("%s\t%d: FAIL:  %s != %s\n", output, i, actualFmt, expectedFmt)
+					outputRenderers = append(outputRenderers, func() string {
+						return fmt.Sprintf("\t%d: FAIL:  %s != %s\n", i, actualFmt(), expectedFmt())
+					})
 				}
 			}
 		}
@@ -1053,7 +1086,12 @@ func (args Arguments) Diff(objects []interface{}) (string, int) {
 		return "No differences.", differences
 	}
 
-	return output, differences
+	outputBuilder.WriteString("\n")
+	for _, r := range outputRenderers {
+		outputBuilder.WriteString(r())
+	}
+
+	return outputBuilder.String(), differences
 }
 
 // Assert compares the arguments with the specified objects and fails if