cmd/compile: check labels and branches during parse time

Instead of a separate check control flow pass (checkcfg.go)
operating on nodes, perform this check at parse time on the
new syntax tree. Permits this check to be done concurrently,
and doesn't depend on the specifics of the symbol's dclstack
implementation anymore. The remaining dclstack uses will be
removed in a follow-up change.

- added CheckBranches Mode flag (so we can turn off the check
  if we only care about syntactic correctness, e.g. for tests)

- adjusted test/goto.go error messages: the new branches
  checker only reports if a goto jumps into a block, but not
  which block (we may want to improve this again, eventually)

- also, the new branches checker reports one variable that
  is being jumped over by a goto, but it may not be the first
  one declared (this is fine either way)

- the new branches checker reports additional errors for
  fixedbugs/issue14006.go (not crucial to avoid those errors)

- the new branches checker now correctly reports only
  variable declarations being jumped over, rather than
  all declarations (issue 8042). Added respective tests.

Fixes #8042.

Change-Id: I53b6e1bda189748e1e1fb5b765a8a64337c27d40
Reviewed-on: https://go-review.googlesource.com/39998
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

1 files changed, 32 insertions, 32 deletions

diff --git a/test/goto.go b/test/goto.go
index f456901a90..6630fb7e34 100644
--- a/test/goto.go
+++ b/test/goto.go
@@ -77,7 +77,7 @@ L:
 
 // error shows first offending variable
 func _() {
-	goto L // ERROR "goto L jumps over declaration of x at LINE+1|goto jumps over declaration"
+	goto L // ERROR "goto L jumps over declaration of x at LINE+1|goto L jumps over declaration of y at LINE+3|goto jumps over declaration"
 	x := 1 // GCCGO_ERROR "defined here"
 	_ = x
 	y := 1
@@ -87,7 +87,7 @@ L:
 
 // goto not okay even if code path is dead
 func _() {
-	goto L // ERROR "goto L jumps over declaration of x at LINE+1|goto jumps over declaration"
+	goto L // ERROR "goto L jumps over declaration of x at LINE+1|goto L jumps over declaration of y at LINE+3|goto jumps over declaration"
 	x := 1 // GCCGO_ERROR "defined here"
 	_ = x
 	y := 1
@@ -114,7 +114,7 @@ L:
 
 // goto into inner block not okay
 func _() {
-	goto L // ERROR "goto L jumps into block starting at LINE+1|goto jumps into block"
+	goto L // ERROR "goto L jumps into block starting at LINE+1|goto L jumps into block|goto jumps into block"
 	{      // GCCGO_ERROR "block starts here"
 	L:
 	}
@@ -125,12 +125,12 @@ func _() {
 	{ // GCCGO_ERROR "block starts here"
 	L:
 	}
-	goto L // ERROR "goto L jumps into block starting at LINE-3|goto jumps into block"
+	goto L // ERROR "goto L jumps into block starting at LINE-3|goto L jumps into block|goto jumps into block"
 }
 
 // error shows first (outermost) offending block
 func _() {
-	goto L // ERROR "goto L jumps into block starting at LINE+1|goto jumps into block"
+	goto L // ERROR "goto L jumps into block starting at LINE+1|goto L jumps into block|goto jumps into block"
 	{
 		{
 			{ // GCCGO_ERROR "block starts here"
@@ -142,7 +142,7 @@ func _() {
 
 // error prefers block diagnostic over declaration diagnostic
 func _() {
-	goto L // ERROR "goto L jumps into block starting at LINE+3|goto jumps into block"
+	goto L // ERROR "goto L jumps into block starting at LINE+3|goto L jumps into block|goto jumps into block"
 	x := 1
 	_ = x
 	{ // GCCGO_ERROR "block starts here"
@@ -179,14 +179,14 @@ L:
 }
 
 func _() {
-	goto L    // ERROR "goto L jumps into block starting at LINE+1|goto jumps into block"
+	goto L    // ERROR "goto L jumps into block starting at LINE+1|goto L jumps into block|goto jumps into block"
 	if true { // GCCGO_ERROR "block starts here"
 	L:
 	}
 }
 
 func _() {
-	goto L    // ERROR "goto L jumps into block starting at LINE+1|goto jumps into block"
+	goto L    // ERROR "goto L jumps into block starting at LINE+1|goto L jumps into block|goto jumps into block"
 	if true { // GCCGO_ERROR "block starts here"
 	L:
 	} else {
@@ -194,7 +194,7 @@ func _() {
 }
 
 func _() {
-	goto L // ERROR "goto L jumps into block starting at LINE+1|goto jumps into block"
+	goto L // ERROR "goto L jumps into block starting at LINE+1|goto L jumps into block|goto jumps into block"
 	if true {
 	} else { // GCCGO_ERROR "block starts here"
 	L:
@@ -205,13 +205,13 @@ func _() {
 	if false { // GCCGO_ERROR "block starts here"
 	L:
 	} else {
-		goto L // ERROR "goto L jumps into block starting at LINE-3|goto jumps into block"
+		goto L // ERROR "goto L jumps into block starting at LINE-3|goto L jumps into block|goto jumps into block"
 	}
 }
 
 func _() {
 	if true {
-		goto L // ERROR "goto L jumps into block starting at LINE+1|goto jumps into block"
+		goto L // ERROR "goto L jumps into block starting at LINE+1|goto L jumps into block|goto jumps into block"
 	} else { // GCCGO_ERROR "block starts here"
 	L:
 	}
@@ -219,7 +219,7 @@ func _() {
 
 func _() {
 	if true {
-		goto L // ERROR "goto L jumps into block starting at LINE+1|goto jumps into block"
+		goto L // ERROR "goto L jumps into block starting at LINE+1|goto L jumps into block|goto jumps into block"
 	} else if false { // GCCGO_ERROR "block starts here"
 	L:
 	}
@@ -227,7 +227,7 @@ func _() {
 
 func _() {
 	if true {
-		goto L // ERROR "goto L jumps into block starting at LINE+1|goto jumps into block"
+		goto L // ERROR "goto L jumps into block starting at LINE+1|goto L jumps into block|goto jumps into block"
 	} else if false { // GCCGO_ERROR "block starts here"
 	L:
 	} else {
@@ -241,7 +241,7 @@ func _() {
 	// really is LINE+1 (like in the previous test),
 	// even though it looks like it might be LINE+3 instead.
 	if true {
-		goto L // ERROR "goto L jumps into block starting at LINE+1|goto jumps into block"
+		goto L // ERROR "goto L jumps into block starting at LINE+1|goto L jumps into block|goto jumps into block"
 	} else if false {
 	} else { // GCCGO_ERROR "block starts here"
 	L:
@@ -290,7 +290,7 @@ func _() {
 	for { // GCCGO_ERROR "block starts here"
 	L:
 	}
-	goto L // ERROR "goto L jumps into block starting at LINE-3|goto jumps into block"
+	goto L // ERROR "goto L jumps into block starting at LINE-3|goto L jumps into block|goto jumps into block"
 }
 
 func _() {
@@ -299,49 +299,49 @@ func _() {
 	L1:
 	}
 L:
-	goto L1 // ERROR "goto L1 jumps into block starting at LINE-5|goto jumps into block"
+	goto L1 // ERROR "goto L1 jumps into block starting at LINE-5|goto L1 jumps into block|goto jumps into block"
 }
 
 func _() {
 	for i < n { // GCCGO_ERROR "block starts here"
 	L:
 	}
-	goto L // ERROR "goto L jumps into block starting at LINE-3|goto jumps into block"
+	goto L // ERROR "goto L jumps into block starting at LINE-3|goto L jumps into block|goto jumps into block"
 }
 
 func _() {
 	for i = 0; i < n; i++ { // GCCGO_ERROR "block starts here"
 	L:
 	}
-	goto L // ERROR "goto L jumps into block starting at LINE-3|goto jumps into block"
+	goto L // ERROR "goto L jumps into block starting at LINE-3|goto L jumps into block|goto jumps into block"
 }
 
 func _() {
 	for i = range x { // GCCGO_ERROR "block starts here"
 	L:
 	}
-	goto L // ERROR "goto L jumps into block starting at LINE-3|goto jumps into block"
+	goto L // ERROR "goto L jumps into block starting at LINE-3|goto L jumps into block|goto jumps into block"
 }
 
 func _() {
 	for i = range c { // GCCGO_ERROR "block starts here"
 	L:
 	}
-	goto L // ERROR "goto L jumps into block starting at LINE-3|goto jumps into block"
+	goto L // ERROR "goto L jumps into block starting at LINE-3|goto L jumps into block|goto jumps into block"
 }
 
 func _() {
 	for i = range m { // GCCGO_ERROR "block starts here"
 	L:
 	}
-	goto L // ERROR "goto L jumps into block starting at LINE-3|goto jumps into block"
+	goto L // ERROR "goto L jumps into block starting at LINE-3|goto L jumps into block|goto jumps into block"
 }
 
 func _() {
 	for i = range s { // GCCGO_ERROR "block starts here"
 	L:
 	}
-	goto L // ERROR "goto L jumps into block starting at LINE-3|goto jumps into block"
+	goto L // ERROR "goto L jumps into block starting at LINE-3|goto L jumps into block|goto jumps into block"
 }
 
 // switch
@@ -395,7 +395,7 @@ func _() {
 }
 
 func _() {
-	goto L // ERROR "goto L jumps into block starting at LINE+1|goto jumps into block"
+	goto L // ERROR "goto L jumps into block starting at LINE+1|goto L jumps into block|goto jumps into block"
 	switch i {
 	case 0:
 	L: // GCCGO_ERROR "block starts here"
@@ -403,7 +403,7 @@ func _() {
 }
 
 func _() {
-	goto L // ERROR "goto L jumps into block starting at LINE+1|goto jumps into block"
+	goto L // ERROR "goto L jumps into block starting at LINE+1|goto L jumps into block|goto jumps into block"
 	switch i {
 	case 0:
 	L: // GCCGO_ERROR "block starts here"
@@ -413,7 +413,7 @@ func _() {
 }
 
 func _() {
-	goto L // ERROR "goto L jumps into block starting at LINE+1|goto jumps into block"
+	goto L // ERROR "goto L jumps into block starting at LINE+1|goto L jumps into block|goto jumps into block"
 	switch i {
 	case 0:
 	default:
@@ -424,7 +424,7 @@ func _() {
 func _() {
 	switch i {
 	default:
-		goto L // ERROR "goto L jumps into block starting at LINE+1|goto jumps into block"
+		goto L // ERROR "goto L jumps into block starting at LINE+1|goto L jumps into block|goto jumps into block"
 	case 0:
 	L: // GCCGO_ERROR "block starts here"
 	}
@@ -436,7 +436,7 @@ func _() {
 	L: // GCCGO_ERROR "block starts here"
 		;
 	default:
-		goto L // ERROR "goto L jumps into block starting at LINE-4|goto jumps into block"
+		goto L // ERROR "goto L jumps into block starting at LINE-4|goto L jumps into block|goto jumps into block"
 	}
 }
 
@@ -492,7 +492,7 @@ func _() {
 }
 
 func _() {
-	goto L // ERROR "goto L jumps into block starting at LINE+2|goto jumps into block"
+	goto L // ERROR "goto L jumps into block starting at LINE+2|goto L jumps into block|goto jumps into block"
 	select {
 	case c <- 1:
 	L: // GCCGO_ERROR "block starts here"
@@ -500,7 +500,7 @@ func _() {
 }
 
 func _() {
-	goto L // ERROR "goto L jumps into block starting at LINE+2|goto jumps into block"
+	goto L // ERROR "goto L jumps into block starting at LINE+2|goto L jumps into block|goto jumps into block"
 	select {
 	case c <- 1:
 	L: // GCCGO_ERROR "block starts here"
@@ -510,7 +510,7 @@ func _() {
 }
 
 func _() {
-	goto L // ERROR "goto L jumps into block starting at LINE+3|goto jumps into block"
+	goto L // ERROR "goto L jumps into block starting at LINE+3|goto L jumps into block|goto jumps into block"
 	select {
 	case <-c:
 	default:
@@ -521,7 +521,7 @@ func _() {
 func _() {
 	select {
 	default:
-		goto L // ERROR "goto L jumps into block starting at LINE+1|goto jumps into block"
+		goto L // ERROR "goto L jumps into block starting at LINE+1|goto L jumps into block|goto jumps into block"
 	case <-c:
 	L: // GCCGO_ERROR "block starts here"
 	}
@@ -533,6 +533,6 @@ func _() {
 	L: // GCCGO_ERROR "block starts here"
 		;
 	default:
-		goto L // ERROR "goto L jumps into block starting at LINE-4|goto jumps into block"
+		goto L // ERROR "goto L jumps into block starting at LINE-4|goto L jumps into block|goto jumps into block"
 	}
 }