go/types: improve recursive type error message

This change improves error message for recursive types.
Currently, compilation of the [following program](https://go.dev/play/p/3ef84ObpzfG):

package main

type T1[T T2] struct{}
type T2[T T1] struct{}

returns an error:

./prog.go:3:6: invalid recursive type T1
	./prog.go:3:6: T1 refers to
	./prog.go:4:6: T2 refers to
	./prog.go:3:6: T1

With the patch applied the error message looks like:

./prog.go:3:6: invalid recursive type T1
	./prog.go:3:6: T1 refers to T2
	./prog.go:4:6: T2 refers to T1

Change-Id: Ic07cdffcffb1483c672b241fede4e694269b5b79
GitHub-Last-Rev: cd042fdc384cf5591b3258ca80fdc002bb8c5e0d
GitHub-Pull-Request: golang/go#69574
Reviewed-on: https://go-review.googlesource.com/c/go/+/614084
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Tim King <taking@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>

diff --git a/src/cmd/compile/internal/types2/decl.go b/src/cmd/compile/internal/types2/decl.go
index 037155a6ca994ccec8d096ff486aabf4fcb0e783..b8e43231a15d31f48e6d60e7e13581fff3fe58e4 100644 (file)
--- a/src/cmd/compile/internal/types2/decl.go
+++ b/src/cmd/compile/internal/types2/decl.go
@@ -334,17 +334,14 @@ func (check *Checker) cycleError(cycle []Object, start int) {
        } else {
                err.addf(obj, "invalid cycle in declaration of %s", objName)
        }
-       i := start
-       for range cycle {
-               err.addf(obj, "%s refers to", objName)
-               i++
-               if i >= len(cycle) {
-                       i = 0
-               }
-               obj = cycle[i]
-               objName = name(obj)
+       // "cycle[i] refers to cycle[j]" for (i,j) = (s, s+1), (s+1, s+2), ..., (n, 0), (0,1), ..., (s-1,s) for len(cycle) = n, s = start.
+       n := len(cycle)
+       rotate := func(i int) int { return (i + start) % n }
+       for i := range n {
+               obj := cycle[rotate(i)]
+               next := cycle[rotate(i+1)]
+               err.addf(obj, "%s refers to %s", name(obj), name(next))
        }
-       err.addf(obj, "%s", objName)
        err.report()
 }
 

diff --git a/src/cmd/compile/internal/types2/initorder.go b/src/cmd/compile/internal/types2/initorder.go
index 09a53c98efe14ce92e41e5981790563552107584..9efbf7f69f8581bc34f2587d27ef43c76b7eafed 100644 (file)
--- a/src/cmd/compile/internal/types2/initorder.go
+++ b/src/cmd/compile/internal/types2/initorder.go
@@ -163,13 +163,11 @@ func (check *Checker) reportCycle(cycle []Object) {
 
        err := check.newError(InvalidInitCycle)
        err.addf(obj, "initialization cycle for %s", obj.Name())
-       // subtle loop: print cycle[i] for i = 0, n-1, n-2, ... 1 for len(cycle) = n
-       for i := len(cycle) - 1; i >= 0; i-- {
-               err.addf(obj, "%s refers to", obj.Name())
-               obj = cycle[i]
+       // "cycle[i] refers to cycle[j]" for (i,j) = (0, n-1), (n-1, n-2), ..., (1,0) for len(cycle) = n.
+       for j := len(cycle) - 1; j >= 0; j-- {
+               err.addf(obj, "%s refers to %s", obj.Name(), cycle[j].Name())
+               obj = cycle[j]
        }
-       // print cycle[0] again to close the cycle
-       err.addf(obj, "%s", obj.Name())
        err.report()
 }
 

diff --git a/src/go/types/decl.go b/src/go/types/decl.go
index 4fd37df786de292c31a73a5d8e1735e078adf218..498eb16f8488291a8c27576a1e15700d4849dcd1 100644 (file)
--- a/src/go/types/decl.go
+++ b/src/go/types/decl.go
@@ -335,17 +335,15 @@ func (check *Checker) cycleError(cycle []Object, start int) {
        } else {
                err.addf(obj, "invalid cycle in declaration of %s", objName)
        }
-       i := start
-       for range cycle {
-               err.addf(obj, "%s refers to", objName)
-               i++
-               if i >= len(cycle) {
-                       i = 0
-               }
-               obj = cycle[i]
-               objName = name(obj)
+
+       // "cycle[i] refers to cycle[j]" for (i,j) = (s, s+1), (s+1, s+2), ..., (n, 0), (0,1), ..., (s-1,s) for len(cycle) = n, s = start.
+       n := len(cycle)
+       rotate := func(i int) int { return (i + start) % n }
+       for i := range n {
+               obj := cycle[rotate(i)]
+               next := cycle[rotate(i+1)]
+               err.addf(obj, "%s refers to %s", name(obj), name(next))
        }
-       err.addf(obj, "%s", objName)
        err.report()
 }
 

diff --git a/src/go/types/initorder.go b/src/go/types/initorder.go
index 077f2eccfe086db6ee459d7d8ccdbc0812b44c8e..682a63e2d738c55ac0f9be67266efeda8670f235 100644 (file)
--- a/src/go/types/initorder.go
+++ b/src/go/types/initorder.go
@@ -166,13 +166,11 @@ func (check *Checker) reportCycle(cycle []Object) {
 
        err := check.newError(InvalidInitCycle)
        err.addf(obj, "initialization cycle for %s", obj.Name())
-       // subtle loop: print cycle[i] for i = 0, n-1, n-2, ... 1 for len(cycle) = n
-       for i := len(cycle) - 1; i >= 0; i-- {
-               err.addf(obj, "%s refers to", obj.Name())
-               obj = cycle[i]
+       // "cycle[i] refers to cycle[j]" for (i,j) = (0, n-1), (n-1, n-2), ..., (1,0) for len(cycle) = n.
+       for j := len(cycle) - 1; j >= 0; j-- {
+               err.addf(obj, "%s refers to %s", obj.Name(), cycle[j].Name())
+               obj = cycle[j]
        }
-       // print cycle[0] again to close the cycle
-       err.addf(obj, "%s", obj.Name())
        err.report()
 }
 

diff --git a/test/fixedbugs/bug195.go b/test/fixedbugs/bug195.go
index 769ed050b3704cf4b1af54bc77512fac4dd7478c..fa9cec75aae876cf6e03142398eb0382b578fdcb 100644 (file)
--- a/test/fixedbugs/bug195.go
+++ b/test/fixedbugs/bug195.go
@@ -18,7 +18,7 @@ type I4 interface { // GC_ERROR "invalid recursive type: I4 refers to itself"
        I4 // GCCGO_ERROR "interface"
 }
 
-type I5 interface { // GC_ERROR "invalid recursive type I5\n\tLINE:.* I5 refers to\n\tLINE+4:.* I6 refers to\n\tLINE:.* I5$"
+type I5 interface { // GC_ERROR "invalid recursive type I5\n\tLINE:.* I5 refers to I6\n\tLINE+4:.* I6 refers to I5$"
        I6
 }
 

diff --git a/test/fixedbugs/issue41575.go b/test/fixedbugs/issue41575.go
index 456873038fc891c8e2d60deebe5cbc368f96aa51..2eed37a94970473a31f36a68634ce8012e24c8bb 100644 (file)
--- a/test/fixedbugs/issue41575.go
+++ b/test/fixedbugs/issue41575.go
@@ -6,7 +6,7 @@
 
 package p
 
-type T1 struct { // ERROR "invalid recursive type T1\n\tLINE: T1 refers to\n\tLINE+4: T2 refers to\n\tLINE: T1$|invalid recursive type"
+type T1 struct { // ERROR "invalid recursive type T1\n.*T1 refers to T2\n.*T2 refers to T1|invalid recursive type"
        f2 T2
 }
 
@@ -15,21 +15,21 @@ type T2 struct { // GCCGO_ERROR "invalid recursive type"
 }
 
 type a b // GCCGO_ERROR "invalid recursive type"
-type b c // ERROR "invalid recursive type b\n\tLINE: b refers to\n\tLINE+1: c refers to\n\tLINE: b$|invalid recursive type"
+type b c // ERROR "invalid recursive type b\n.*b refers to c\n.*c refers to b|invalid recursive type|invalid recursive type"
 type c b // GCCGO_ERROR "invalid recursive type"
 
 type d e
 type e f
-type f f // ERROR "invalid recursive type f\n\tLINE: f refers to\n\tLINE: f$|invalid recursive type"
+type f f // ERROR "invalid recursive type: f refers to itself|invalid recursive type|invalid recursive type"
 
-type g struct { // ERROR "invalid recursive type g\n\tLINE: g refers to\n\tLINE: g$|invalid recursive type"
+type g struct { // ERROR "invalid recursive type: g refers to itself|invalid recursive type"
        h struct {
                g
        }
 }
 
 type w x
-type x y           // ERROR "invalid recursive type x\n\tLINE: x refers to\n\tLINE+1: y refers to\n\tLINE+2: z refers to\n\tLINE: x$|invalid recursive type"
+type x y           // ERROR "invalid recursive type x\n.*x refers to y\n.*y refers to z\n.*z refers to x|invalid recursive type"
 type y struct{ z } // GCCGO_ERROR "invalid recursive type"
 type z [10]x
 

diff --git a/test/fixedbugs/issue50788.dir/b.go b/test/fixedbugs/issue50788.dir/b.go
index e17afc7b4330992df3392f29869642a5fb9e7cff..97ae20801985abdbb3bfc3dd07f2902b6c93771e 100644 (file)
--- a/test/fixedbugs/issue50788.dir/b.go
+++ b/test/fixedbugs/issue50788.dir/b.go
@@ -6,4 +6,4 @@ package b
 
 import "./a"
 
-type T a.T[T] // ERROR "invalid recursive type T\n.*T refers to\n.*a\.T refers to\n.*T"
+type T a.T[T] // ERROR "invalid recursive type T\n.*T refers to a\.T\n.*a\.T refers to T"

diff --git a/test/initloop.go b/test/initloop.go
index b1a8470b3a0b15b3824375f24b34509def075fbe..c4530f36d6c24d3d27f5fbf5c7f46db2dcdf2297 100644 (file)
--- a/test/initloop.go
+++ b/test/initloop.go
@@ -11,7 +11,7 @@ package main
 
 var (
        x int = a
-       a int = b // ERROR "a refers to\n.*b refers to\n.*c refers to\n.*a|initialization loop"
+       a int = b // ERROR "a refers to b\n.*b refers to c\n.*c refers to a|initialization loop"
        b int = c
        c int = a
 )