fix and test cases

testdata/src/go.uber.org/errormessage/errormessage.go

@@ -48,7 +48,8 @@ func test3(x *int) {
 
 // nilable(f)
 type S struct {
-	f *int
+	f    *int
+	sPtr *S
 }
 
 func test4(x *int) {
@@ -147,3 +148,56 @@ func test13() *int {
 	}
 	return new(int)
 }
+
+// below tests check shortening of expressions
+
+// nilable(s, result 0)
+func (s *S) bar(i int) *int {
+	return nil
+}
+
+// nilable(result 0)
+func (s *S) retNil(a int, b *int, c string, d bool) *S {
+	return nil
+}
+
+func test14(x *int, i int) {
+	s := &S{}
+	x = s.retNil(1,
+		new(int),
+		"abc",
+		true).bar(i)
+	y := x
+	print(*y) //want "`s.retNil\\(...\\).bar\\(i\\)` to `x`"
+}
+
+func test15(x *int) {
+	var longVarName, anotherLongVarName, yetAnotherLongName int
+	s := &S{}
+	x = s.retNil(longVarName, &anotherLongVarName, "abc", true).bar(yetAnotherLongName)
+	y := x
+	print(*y) //want "`s.retNil\\(...\\).bar\\(...\\)` to `x`"
+}
+
+func test16(mp map[int]*int) {
+	var aVeryVeryVeryLongIndexVar int
+	x := mp[aVeryVeryVeryLongIndexVar]
+	y := x
+	print(*y) //want "`mp\\[...\\]` to `x`"
+}
+
+func test17(x *int, mp map[int]*int) {
+	var aVeryVeryVeryLongIndexVar int
+	s := &S{}
+
+	x = s.retNil(1, mp[aVeryVeryVeryLongIndexVar], "abc", true).bar(2) //want "deep read"
+	y := x
+	print(*y) //want "`s.retNil\\(...\\).bar\\(2\\)` to `x`"
+}
+
+func test18(x *int, mp map[int]*int) {
+	s := &S{}
+	x = mp[*(s.retNil(1, new(int), "abc", true).bar(2))] //want "dereferenced"
+	y := x
+	print(*y) //want "`mp\\[...\\]` to `x`"
+}

util/util.go

@@ -516,30 +516,31 @@ func ExprToString(e ast.Expr, pass *analysis.Pass, isShortenExpr bool) string {
 // exprOnLine3)" becomes "foo(...)"
 func shortenExpr(expr string) string {
 	var result strings.Builder
-	var depth int
-	var inBrackets bool
-	var innerExpr strings.Builder
+	var depth int                 // helps to keep track of nested brackets
+	var inBrackets bool           // indicates if we are currently inside brackets
+	var innerExpr strings.Builder // stores the content inside brackets
 
 	for _, char := range expr {
 		switch char {
 		case '(', '{', '[':
 			if depth == 0 {
-				depth++
 				inBrackets = true
-				result.WriteRune(char)
+				result.WriteRune(char) // append the opening bracket
 			}
+			depth++
 			continue
 
 		case ')', '}', ']':
 			depth--
 			if depth == 0 {
-				// Replace the content inside brackets with "..." if it is long (more than 3 characters)
+				// Replace the content inside brackets with "..." if it is long (more than 3 characters), else
+				// retain the original content as is.
 				if innerExpr.Len() > 3 {
 					result.WriteString("...")
 				} else {
 					result.WriteString(innerExpr.String())
 				}
-				result.WriteRune(char)
+				result.WriteRune(char) // append the closing bracket
 
 				inBrackets = false
 				innerExpr.Reset()
@@ -548,10 +549,10 @@ func shortenExpr(expr string) string {
 		}
 
 		if inBrackets {
-			innerExpr.WriteRune(char)
+			innerExpr.WriteRune(char) // append the character to the inner expression
 			continue
 		}
-		result.WriteRune(char)
+		result.WriteRune(char) // append the character to the result if not in brackets, and not a bracket itself
 	}
 
 	return result.String()