strparse implementation

Author: quasilyte

strparse.go

@@ -0,0 +1,55 @@
+// Package strparse provides convenience wrappers around `go/parser` for simple
+// expression, statement and declaretion parsing from string.
+//
+// Can be used to construct AST nodes using source syntax.
+package strparse
+
+import (
+	"go/ast"
+	"go/parser"
+	"go/token"
+)
+
+var (
+	// BadExpr is returned as a parse result for malformed expressions.
+	// Should be treated as constant or readonly variable.
+	BadExpr = &ast.BadExpr{}
+
+	// BadStmt is returned as a parse result for malformed statmenents.
+	// Should be treated as constant or readonly variable.
+	BadStmt = &ast.BadStmt{}
+
+	// BadDecl is returned as a parse result for malformed declarations.
+	// Should be treated as constant or readonly variable.
+	BadDecl = &ast.BadDecl{}
+)
+
+// Expr parses single expression node from s.
+// In case of parse error, BadExpr is returned.
+func Expr(s string) ast.Expr {
+	node, err := parser.ParseExpr(s)
+	if err != nil {
+		return BadExpr
+	}
+	return node
+}
+
+// Stmt parses single statement node from s.
+// In case of parse error, BadStmt is returned.
+func Stmt(s string) ast.Stmt {
+	node, err := parser.ParseFile(token.NewFileSet(), "", "package main;func main() {"+s+"}", 0)
+	if err != nil {
+		return BadStmt
+	}
+	return node.Decls[0].(*ast.FuncDecl).Body.List[0]
+}
+
+// Decl parses single declaration node from s.
+// In case of parse error, BadDecl is returned.
+func Decl(s string) ast.Decl {
+	node, err := parser.ParseFile(token.NewFileSet(), "", "package main;"+s, 0)
+	if err != nil {
+		return BadDecl
+	}
+	return node.Decls[0]
+}

strparse_test.go

@@ -0,0 +1,48 @@
+package strparse
+
+import (
+	"bytes"
+	"fmt"
+	"go/ast"
+	"go/format"
+	"go/token"
+	"testing"
+)
+
+func equalPrintedForm(x ast.Node, y string) bool {
+	var buf bytes.Buffer
+	if err := format.Node(&buf, token.NewFileSet(), x); err != nil {
+		panic(fmt.Sprintf("format error: %v", err))
+	}
+	b, err := format.Source([]byte(y))
+	if err != nil {
+		panic(fmt.Sprintf("format error: %v", err))
+	}
+	xString := buf.String()
+	yString := string(b)
+	return xString == yString
+}
+
+func TestParseExpr(t *testing.T) {
+	const input = `1 * (2 << x)/s[1].f()(^y)`
+	expr := Expr(input)
+	if !equalPrintedForm(expr, input) {
+		t.Error("expr printed form not match")
+	}
+}
+
+func TestParseStmt(t *testing.T) {
+	const input = `for i := 0; i < len(xs); i++ { fmt.Println(i) }`
+	expr := Stmt(input)
+	if !equalPrintedForm(expr, input) {
+		t.Error("stmt printed form not match")
+	}
+}
+
+func TestParseDecl(t *testing.T) {
+	const input = `var (x int = 19; a, b = f(); c, d = "1", "2"+"3")`
+	expr := Decl(input)
+	if !equalPrintedForm(expr, input) {
+		t.Error("decl printed form not match")
+	}
+}