From a835c872fcea276c439f23036693a44975ace28c Mon Sep 17 00:00:00 2001
From: Muir Manders <muir@mnd.rs>
Date: Sat, 5 Dec 2020 12:43:06 -0800
Subject: [PATCH] internal/lsp/source: omit assign stmt LHS in RHS completion

In the below example:

    fooBar := fooB<>

We will no longer suggest "fooBar" at <>.

Fixes golang/go#39203.

Change-Id: Ie1450397ce3de4f21fb0862c1a4f0fe2812325fd
Reviewed-on: https://go-review.googlesource.com/c/tools/+/275693
Run-TryBot: Muir Manders <muir@mnd.rs>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>
Trust: Rebecca Stambler <rstambler@golang.org>
Trust: Robert Findley <rfindley@google.com>
---
 internal/lsp/source/completion/completion.go | 10 ++++------
 internal/lsp/source/completion/util.go       | 17 ++++++++++++++---
 internal/lsp/testdata/assign/assign.go.in    |  8 ++++++++
 internal/lsp/testdata/summary.txt.golden     |  2 +-
 4 files changed, 27 insertions(+), 10 deletions(-)

diff --git a/internal/lsp/source/completion/completion.go b/internal/lsp/source/completion/completion.go
index e720e78cc0..14afb8f58e 100644
--- a/internal/lsp/source/completion/completion.go
+++ b/internal/lsp/source/completion/completion.go
@@ -1284,12 +1284,10 @@ func (c *completer) lexical(ctx context.Context) error {
 				}
 			}
 
-			// Don't use LHS of value spec in RHS.
-			if vs := enclosingValueSpec(c.path); vs != nil {
-				for _, ident := range vs.Names {
-					if obj.Pos() == ident.Pos() {
-						continue Names
-					}
+			// Don't use LHS of decl in RHS.
+			for _, ident := range enclosingDeclLHS(c.path) {
+				if obj.Pos() == ident.Pos() {
+					continue Names
 				}
 			}
 
diff --git a/internal/lsp/source/completion/util.go b/internal/lsp/source/completion/util.go
index 6d0883e0ff..673390625d 100644
--- a/internal/lsp/source/completion/util.go
+++ b/internal/lsp/source/completion/util.go
@@ -195,10 +195,21 @@ func enclosingSelector(path []ast.Node, pos token.Pos) *ast.SelectorExpr {
 	return nil
 }
 
-func enclosingValueSpec(path []ast.Node) *ast.ValueSpec {
+// enclosingDeclLHS returns LHS idents from containing value spec or
+// assign statement.
+func enclosingDeclLHS(path []ast.Node) []*ast.Ident {
 	for _, n := range path {
-		if vs, ok := n.(*ast.ValueSpec); ok {
-			return vs
+		switch n := n.(type) {
+		case *ast.ValueSpec:
+			return n.Names
+		case *ast.AssignStmt:
+			ids := make([]*ast.Ident, 0, len(n.Lhs))
+			for _, e := range n.Lhs {
+				if id, ok := e.(*ast.Ident); ok {
+					ids = append(ids, id)
+				}
+			}
+			return ids
 		}
 	}
 
diff --git a/internal/lsp/testdata/assign/assign.go.in b/internal/lsp/testdata/assign/assign.go.in
index 3fe256e66b..8c00ae9e0e 100644
--- a/internal/lsp/testdata/assign/assign.go.in
+++ b/internal/lsp/testdata/assign/assign.go.in
@@ -16,3 +16,11 @@ func _() {
 func _() {
 	var a string = a //@complete(" //")
 }
+
+func _() {
+	fooBar := fooBa //@complete(" //"),item(assignFooBar, "fooBar", "", "var")
+	abc, fooBar := 123, fooBa //@complete(" //", assignFooBar)
+	{
+		fooBar := fooBa //@complete(" //", assignFooBar)
+	}
+}
diff --git a/internal/lsp/testdata/summary.txt.golden b/internal/lsp/testdata/summary.txt.golden
index 8d095cbb51..a2bb47340b 100644
--- a/internal/lsp/testdata/summary.txt.golden
+++ b/internal/lsp/testdata/summary.txt.golden
@@ -1,7 +1,7 @@
 -- summary --
 CallHierarchyCount = 1
 CodeLensCount = 5
-CompletionsCount = 255
+CompletionsCount = 258
 CompletionSnippetCount = 88
 UnimportedCompletionsCount = 5
 DeepCompletionsCount = 5