x/tools: be defensive after types.Info.Types[expr] lookups

This CL is the result of a quick audit
of x/tools for places that look in the Types map and do
not handle missing entries gracefully (unless dominated
by a check for welltypedness, such as RunDespiteErrors:false
in the analysis framework). In each case it either adds
a defensive check or documents the assumption.

See golang/go#69092 (comment)

Updates golang/go#69092

Change-Id: I3573512fd47ee4dca2e0b4bce2803b92424d7037
Reviewed-on: https://go-review.googlesource.com/c/tools/+/617416
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Robert Findley <[email protected]>
Auto-Submit: Alan Donovan <[email protected]>

go/types/internal/play/play.go

@@ -194,8 +194,10 @@ func handleSelectJSON(w http.ResponseWriter, req *http.Request) {
 			if tv.Value != nil {
 				fmt.Fprintf(out, ", and constant value %v", tv.Value)
 			}
-			fmt.Fprintf(out, "\n\n")
+		} else {
+			fmt.Fprintf(out, "%T has no type", innermostExpr)
 		}
+		fmt.Fprintf(out, "\n\n")
 	}
 
 	// selection x.f information (if cursor is over .f)

gopls/internal/cache/testfuncs/tests.go

@@ -156,7 +156,7 @@ func (b *indexBuilder) findSubtests(parent gobTest, typ *ast.FuncType, body *ast
 			continue // subtest has wrong signature
 		}
 
-		val := info.Types[call.Args[0]].Value
+		val := info.Types[call.Args[0]].Value // may be zero
 		if val == nil || val.Kind() != constant.String {
 			continue
 		}

gopls/internal/golang/completion/printf.go

@@ -40,7 +40,7 @@ func printfArgKind(info *types.Info, call *ast.CallExpr, argIdx int) objKind {
 	}
 
 	// Format string must be a constant.
-	strArg := info.Types[call.Args[numParams-2]].Value
+	strArg := info.Types[call.Args[numParams-2]].Value // may be zero
 	if strArg == nil || strArg.Kind() != constant.String {
 		return kindAny
 	}

gopls/internal/golang/freesymbols.go

@@ -372,7 +372,11 @@ func freeRefs(pkg *types.Package, info *types.Info, file *ast.File, start, end t
 
 			if ref != nil {
 				ref.expr = n.(ast.Expr)
-				ref.typ = info.Types[n.(ast.Expr)].Type
+				if tv, ok := info.Types[ref.expr]; ok {
+					ref.typ = tv.Type
+				} else {
+					ref.typ = types.Typ[types.Invalid]
+				}
 				free = append(free, ref)
 			}
 

gopls/internal/golang/highlight.go

@@ -558,8 +558,6 @@ func highlightIdentifier(id *ast.Ident, file *ast.File, info *types.Info, result
 			highlightWriteInExpr(n.Chan)
 		case *ast.CompositeLit:
 			t := info.TypeOf(n)
-			// Every expression should have a type;
-			// work around https://github.com/golang/go/issues/69092.
 			if t == nil {
 				t = types.Typ[types.Invalid]
 			}

gopls/internal/golang/identifier.go

@@ -175,7 +175,7 @@ Outer:
 	var typ types.Type
 	if assign, ok := ts.Assign.(*ast.AssignStmt); ok && len(assign.Rhs) == 1 {
 		if rhs := assign.Rhs[0].(*ast.TypeAssertExpr); ok {
-			typ = info.TypeOf(rhs.X)
+			typ = info.TypeOf(rhs.X) // may be nil
 		}
 	}
 	return objs, typ

internal/refactor/inline/escape.go

@@ -41,10 +41,13 @@ func escape(info *types.Info, root ast.Node, f func(v *types.Var, escapes bool))
 			//
 			// We must traverse the normal terms and check
 			// whether any of them is an array.
+			//
+			// We assume TypeOf returns non-nil.
 			if _, ok := info.TypeOf(e.X).Underlying().(*types.Array); ok {
 				lvalue(e.X, escapes) // &a[i] on array
 			}
 		case *ast.SelectorExpr:
+			// We assume TypeOf returns non-nil.
 			if _, ok := info.TypeOf(e.X).Underlying().(*types.Struct); ok {
 				lvalue(e.X, escapes) // &s.f on struct
 			}

internal/typeparams/genericfeatures/features.go

@@ -80,7 +80,7 @@ func ForPackage(inspect *inspector.Inspector, info *types.Info) Features {
 				direct |= GenericFuncDecls
 			}
 		case *ast.InterfaceType:
-			tv := info.Types[n]
+			tv := info.Types[n] // may be zero
 			if iface, _ := tv.Type.(*types.Interface); iface != nil && !iface.IsMethodSet() {
 				direct |= EmbeddedTypeSets
 			}