go/types: clarify that contexts do not guarantee deduplication

Documentation around the use of types.Context is unclear about whether
contexts guarantee deduplication of identical instances. Add explicit
disclaimers that this is not the case.

Fixes golang/go#51680

Change-Id: I6651587315d3cbf9e8d70a69d3e2ec5cedd00da5
Reviewed-on: https://go-review.googlesource.com/c/go/+/396536
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

diff --git a/src/cmd/compile/internal/types2/context.go b/src/cmd/compile/internal/types2/context.go
index 7abea6b654b34dd738a707c21c3cd11a3ee48669..2d790fe5dddbbf30aa025241daeadfb3a7c2c595 100644 (file)
--- a/src/cmd/compile/internal/types2/context.go
+++ b/src/cmd/compile/internal/types2/context.go
@@ -12,11 +12,12 @@ import (
        "sync"
 )
 
-// An Context is an opaque type checking context. It may be used to share
+// A Context is an opaque type checking context. It may be used to share
 // identical type instances across type-checked packages or calls to
-// Instantiate.
+// Instantiate. Contexts are safe for concurrent use.
 //
-// It is safe for concurrent use.
+// The use of a shared context does not guarantee that identical instances are
+// deduplicated in all cases.
 type Context struct {
        mu        sync.Mutex
        typeMap   map[string][]ctxtEntry // type hash -> instances entries

diff --git a/src/cmd/compile/internal/types2/instantiate.go b/src/cmd/compile/internal/types2/instantiate.go
index a511538ccc6b3387c06b46b988912e517561266c..a69a26ba648bd83ccfd03bc77a02cdb05201bb3a 100644 (file)
--- a/src/cmd/compile/internal/types2/instantiate.go
+++ b/src/cmd/compile/internal/types2/instantiate.go
@@ -24,7 +24,8 @@ import (
 // previous instances with the same identity. As a special case, generic
 // *Signature origin types are only considered identical if they are pointer
 // equivalent, so that instantiating distinct (but possibly identical)
-// signatures will yield different instances.
+// signatures will yield different instances. The use of a shared context does
+// not guarantee that identical instances are deduplicated in all cases.
 //
 // If validate is set, Instantiate verifies that the number of type arguments
 // and parameters match, and that the type arguments satisfy their

diff --git a/src/go/types/context.go b/src/go/types/context.go
index ff4bf89f3cb0076abca2a199c2288bee980276a9..692b3a66828a9c593432c1a8a4ad92fc9be0f626 100644 (file)
--- a/src/go/types/context.go
+++ b/src/go/types/context.go
@@ -12,11 +12,12 @@ import (
        "sync"
 )
 
-// An Context is an opaque type checking context. It may be used to share
+// A Context is an opaque type checking context. It may be used to share
 // identical type instances across type-checked packages or calls to
-// Instantiate.
+// Instantiate. Contexts are safe for concurrent use.
 //
-// It is safe for concurrent use.
+// The use of a shared context does not guarantee that identical instances are
+// deduplicated in all cases.
 type Context struct {
        mu        sync.Mutex
        typeMap   map[string][]ctxtEntry // type hash -> instances entries

diff --git a/src/go/types/instantiate.go b/src/go/types/instantiate.go
index d7045ff23c0fef11decc8aca46034f1ec52726e6..4450847dfdaff12f94e73962e18b405c70250ce3 100644 (file)
--- a/src/go/types/instantiate.go
+++ b/src/go/types/instantiate.go
@@ -24,7 +24,8 @@ import (
 // previous instances with the same identity. As a special case, generic
 // *Signature origin types are only considered identical if they are pointer
 // equivalent, so that instantiating distinct (but possibly identical)
-// signatures will yield different instances.
+// signatures will yield different instances. The use of a shared context does
+// not guarantee that identical instances are deduplicated in all cases.
 //
 // If validate is set, Instantiate verifies that the number of type arguments
 // and parameters match, and that the type arguments satisfy their