From 89925d5a5697fa80aaf2c7eb2ac78833a61b7436 Mon Sep 17 00:00:00 2001
From: Martin Angers <martin.n.angers@gmail.com>
Date: Sat, 1 Feb 2020 18:11:08 -0500
Subject: [PATCH] pkg/codegen: start building the Go AST

---
 pkg/codegen/codegen.go   |  9 +++---
 pkg/codegen/treebuild.go | 64 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 69 insertions(+), 4 deletions(-)
 create mode 100644 pkg/codegen/treebuild.go

diff --git a/pkg/codegen/codegen.go b/pkg/codegen/codegen.go
index 3ae24a1..3dc7085 100644
--- a/pkg/codegen/codegen.go
+++ b/pkg/codegen/codegen.go
@@ -81,12 +81,13 @@ func ExecUnit(outDir string, unit *semantic.Unit) ([]string, error) {
 	}
 	semantic.Walk(t, unit)
 
-	// TODO: temp, just to avoid errors, will require 4.
-	gofiles := make([]*goast.File, len(unit.Files))
-
-	// TODO: 4
 	// 4. build the Go AST tree from the Snow-associated nodes so that relative
 	//    position of nodes respects the snow source
+	tb := &treebuilder{
+		nodeToGoAST: t.nodeToGoAST,
+	}
+	semantic.Walk(tb, unit)
+	gofiles := tb.gofiles
 
 	// 5. walk the Go AST and assign valid positions to nodes
 	fset := token.NewFileSet()
diff --git a/pkg/codegen/treebuild.go b/pkg/codegen/treebuild.go
new file mode 100644
index 0000000..7b33e69
--- /dev/null
+++ b/pkg/codegen/treebuild.go
@@ -0,0 +1,64 @@
+package codegen
+
+import (
+	goast "go/ast"
+
+	"git.sr.ht/~mna/snow/pkg/semantic"
+)
+
+// The treebuilder builds the Go AST from the nodes associated with the
+// abstract semantic graph in the translator phase.
+type treebuilder struct {
+	curGoFile   *goast.File
+	gofiles     []*goast.File
+	nodeToGoAST map[semantic.Node][]goast.Node
+}
+
+func (tb *treebuilder) Visit(n semantic.Node) semantic.Visitor {
+	switch n := n.(type) {
+	case *semantic.Unit:
+		for _, f := range n.Files {
+			semantic.Walk(tb, f)
+			tb.gofiles = append(tb.gofiles, tb.curGoFile)
+		}
+
+	case *semantic.File:
+		// file node should have its goast.File as first node, rest should be added
+		// to the file's declarations.
+		ns := tb.nodeToGoAST[n]
+		tb.curGoFile = ns[0].(*goast.File)
+		for i := 1; i < len(ns); i++ {
+			tb.curGoFile.Decls = append(tb.curGoFile.Decls, ns[i].(goast.Decl))
+		}
+
+		decls := make([]semantic.Decl, 0, len(n.Vars)+len(n.Structs)+len(n.Fns))
+		for _, v := range n.Vars {
+			semantic.Walk(tb, v)
+			decls = append(decls, v)
+		}
+		for _, str := range n.Structs {
+			semantic.Walk(tb, str)
+			decls = append(decls, str)
+		}
+		for _, fn := range n.Fns {
+			semantic.Walk(tb, fn)
+			decls = append(decls, fn)
+		}
+		for _, decl := range decls {
+			for _, gons := range tb.nodeToGoAST[decl] {
+				tb.curGoFile.Decls = append(tb.curGoFile.Decls, gons.(goast.Decl))
+			}
+		}
+
+	case *semantic.Fn:
+	case *semantic.Struct:
+	case *semantic.Var:
+	case *semantic.Block:
+	case *semantic.Return:
+	case *semantic.Assign:
+	case *semantic.ExprStmt:
+	case *semantic.If:
+	case *semantic.Guard:
+	}
+	return nil
+}
-- 
2.45.2