go/analysis/passes/shadow: separate package-level variables logic

Author: bkreitch

go/analysis/passes/shadow/shadow.go

@@ -42,6 +42,8 @@ func run(pass *analysis.Pass) (any, error) {
 	inspect := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)
 
 	spans := make(map[types.Object]span)
+	usedPkgVars := make(map[types.Object]struct{})
+
 	for id, obj := range pass.TypesInfo.Defs {
 		// Ignore identifiers that don't denote objects
 		// (package names, symbolic variables such as t
@@ -52,6 +54,10 @@ func run(pass *analysis.Pass) (any, error) {
 	}
 	for id, obj := range pass.TypesInfo.Uses {
 		growSpan(spans, obj, id.Pos(), id.End())
+		// Track usage for package-level variables.
+		if obj.Parent() == obj.Pkg().Scope() {
+			usedPkgVars[obj] = struct{}{}
+		}
 	}
 	for node, obj := range pass.TypesInfo.Implicits {
 		// A type switch with a short variable declaration
@@ -74,9 +80,9 @@ func run(pass *analysis.Pass) (any, error) {
 	inspect.Preorder(nodeFilter, func(n ast.Node) {
 		switch n := n.(type) {
 		case *ast.AssignStmt:
-			checkShadowAssignment(pass, spans, n)
+			checkShadowAssignment(pass, spans, usedPkgVars, n)
 		case *ast.GenDecl:
-			checkShadowDecl(pass, spans, n)
+			checkShadowDecl(pass, spans, usedPkgVars, n)
 		}
 	})
 	return nil, nil
@@ -131,7 +137,7 @@ func growSpan(spans map[types.Object]span, obj types.Object, pos, end token.Pos)
 }
 
 // checkShadowAssignment checks for shadowing in a short variable declaration.
-func checkShadowAssignment(pass *analysis.Pass, spans map[types.Object]span, a *ast.AssignStmt) {
+func checkShadowAssignment(pass *analysis.Pass, spans map[types.Object]span, usedPkgVars map[types.Object]struct{}, a *ast.AssignStmt) {
 	if a.Tok != token.DEFINE {
 		return
 	}
@@ -144,7 +150,7 @@ func checkShadowAssignment(pass *analysis.Pass, spans map[types.Object]span, a *
 			pass.ReportRangef(expr, "invalid AST: short variable declaration of non-identifier")
 			return
 		}
-		checkShadowing(pass, spans, ident)
+		checkShadowing(pass, spans, usedPkgVars, ident)
 	}
 }
 
@@ -204,7 +210,7 @@ func idiomaticRedecl(d *ast.ValueSpec) bool {
 }
 
 // checkShadowDecl checks for shadowing in a general variable declaration.
-func checkShadowDecl(pass *analysis.Pass, spans map[types.Object]span, d *ast.GenDecl) {
+func checkShadowDecl(pass *analysis.Pass, spans map[types.Object]span, usedPkgVars map[types.Object]struct{}, d *ast.GenDecl) {
 	if d.Tok != token.VAR {
 		return
 	}
@@ -220,13 +226,13 @@ func checkShadowDecl(pass *analysis.Pass, spans map[types.Object]span, d *ast.Ge
 			return
 		}
 		for _, ident := range valueSpec.Names {
-			checkShadowing(pass, spans, ident)
+			checkShadowing(pass, spans, usedPkgVars, ident)
 		}
 	}
 }
 
 // checkShadowing checks whether the identifier shadows an identifier in an outer scope.
-func checkShadowing(pass *analysis.Pass, spans map[types.Object]span, ident *ast.Ident) {
+func checkShadowing(pass *analysis.Pass, spans map[types.Object]span, usedPkgVars map[types.Object]struct{}, ident *ast.Ident) {
 	if ident.Name == "_" {
 		// Can't shadow the blank identifier.
 		return
@@ -249,23 +255,31 @@ func checkShadowing(pass *analysis.Pass, spans map[types.Object]span, ident *ast
 	shadowedPos := pass.Fset.Position(shadowed.Pos())
 	identPos := pass.Fset.Position(ident.Pos())
 
-	if strict {
-		// The shadowed identifier must appear before this one to be an instance of shadowing.
-		if shadowed.Pos() > ident.Pos() {
-			return
+	// Check if the shadowed variable is at package level.
+	if shadowed.Parent() == shadowed.Pkg().Scope() {
+		if !strict {
+			// Don't complain if the package variable is unused.
+			if _, ok := usedPkgVars[shadowed]; !ok {
+				return
+			}
 		}
 	} else {
-		// Don't complain if the span of validity of the shadowed identifier doesn't include
-		// the shadowing identifier, except for cross-file shadowing where file processing
-		// order affects span checks.
-		span, ok := spans[shadowed]
-		if !ok {
-			pass.ReportRangef(ident, "internal error: no range for %q", ident.Name)
-			return
-		}
-
-		if shadowedPos.Filename == identPos.Filename && !span.contains(ident.Pos()) {
-			return
+		if strict {
+			// The shadowed identifier must appear before this one to be an instance of shadowing.
+			if shadowed.Pos() > ident.Pos() {
+				return
+			}
+		} else {
+			// Don't complain if the span of validity of the shadowed identifier doesn't include
+			// the shadowing identifier.
+			span, ok := spans[shadowed]
+			if !ok {
+				pass.ReportRangef(ident, "internal error: no range for %q", ident.Name)
+				return
+			}
+			if !span.contains(ident.Pos()) {
+				return
+			}
 		}
 	}
 	// Don't complain if the types differ: that implies the programmer really wants two different things.

go/analysis/passes/shadow/testdata/src/crossfile/crossfile.go

@@ -8,8 +8,10 @@ package crossfile
 
 func ShadowGlobal() {
 	{
-		global := 1 // want "declaration of .global. shadows declaration at line 7 in other.go"
+		global := 1 // want "declaration of .global. shadows declaration at line 8 in other.go"
 		_ = global
+		unusedGlobal := 2 // OK - shadowed package variable is never used
+		_ = unusedGlobal
 	}
 	_ = global
 }

go/analysis/passes/shadow/testdata/src/crossfile/other.go

@@ -4,4 +4,7 @@
 
 package crossfile
 
-var global int
+var (
+	global       int
+	unusedGlobal int
+)