gopls/internal/golang/hover: show alias real type decl for types only

The existing hover tries to get the real type decl for all kinds of
objects, which makes the returned hoverResult contains a non-empty
typeDecl for a var.

As a result, hovering over 'alias' gets wrong output 'type Named int'
rather than expected 'var alias Alias'.

	type Named int
	type Alias = Named
	var alias Alias

This CL has fixed this wrong behavior by getting typeDecl only if the
object is a type, including type parameter. So hovering over a variable
will behave correctly.

Fixes golang/go#74361

Change-Id: I64cac07bc92ebfbd113fd2dac78eecb2ef8426cc
Reviewed-on: https://go-review.googlesource.com/c/tools/+/685775
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Robert Findley <[email protected]>
Reviewed-by: Mark Freeman <[email protected]>

Author: xieyuschen

gopls/internal/golang/hover.go

@@ -556,10 +556,15 @@ func hover(ctx context.Context, snapshot *cache.Snapshot, fh file.Handle, pp pro
 		}
 	}
 
-	// realTypeDecl is defined to store the underlying definition of an alias.
-	realTypeDecl, _ := findRhsTypeDecl(ctx, snapshot, pkg, obj) // tolerate the error
-	if realTypeDecl != "" {
-		typeDecl += fmt.Sprintf("\n\n%s", realTypeDecl)
+	if isTypeName {
+		// get the real type decl only if current object is a type,
+		// for non-types, we'd better hide the real type decl to avoid possible confusion.
+		//
+		// realTypeDecl is defined to store the underlying definition of an alias.
+		realTypeDecl, _ := findRhsTypeDecl(ctx, snapshot, pkg, obj) // tolerate the error
+		if realTypeDecl != "" {
+			typeDecl += fmt.Sprintf("\n\n%s", realTypeDecl)
+		}
 	}
 
 	// Compute link data (on pkg.go.dev or other documentation host).

gopls/internal/test/marker/testdata/hover/hover_alias.txt

@@ -6,6 +6,8 @@ This test checks gopls behavior when hovering over alias type.
 -- go.mod --
 module mod.com
 
+go 1.18
+
 -- main.go --
 package main
 
@@ -35,6 +37,17 @@ type RealType struct {
 	Age int
 }
 
+-- generic/a.go --
+package generic
+func generic[T any]() {}
+
+type Named string
+type Alias = Named
+
+func _(){
+	generic[Alias]() //@hover("Alias", "Alias", Alias)
+}
+
 -- @ToTypeDecl --
 ```go
 type ToTypeDecl = b.RealType // size=24 (0x18)
@@ -79,3 +92,13 @@ type ToAliasWithComment = a.AliasWithComment // size=24 (0x18)
 ---
 
 [`main.ToAliasWithComment` on pkg.go.dev](https://pkg.go.dev/mod.com#ToAliasWithComment)
+-- @Alias --
+```go
+type Alias = Named
+
+type Named string
+```
+
+---
+
+[`generic.Alias` on pkg.go.dev](https://pkg.go.dev/mod.com/generic#Alias)

gopls/internal/test/marker/testdata/hover/issue74361.txt

@@ -0,0 +1,40 @@
+-- flags --
+-skip_goarch=386,arm
+
+-- settings.json --
+{"analyses": {"unusedfunc": false}}
+
+-- go.mod --
+module mod.com
+
+-- a/a.go --
+package a
+
+type (
+	Named  int
+	Alias  = Named
+	Alias2 = Alias
+)
+
+var (
+	named  Named
+	alias  Alias //@hover("alias", "alias", alias)
+	alias2 Alias2 //@hover("alias2", "alias2", alias2)
+)
+
+-- @alias --
+```go
+var alias Alias
+```
+
+---
+
+@hover("alias", "alias", alias)
+-- @alias2 --
+```go
+var alias2 Alias2
+```
+
+---
+
+@hover("alias2", "alias2", alias2)