Added DSLSymbols

These are new APIs to manage symbols and symbol tables from DSL code,
needed for the upcoming DSLParser.

Change-Id: Ic8d86aebfbcdeb84bd872d8727cdfafbb8db2fd6
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/414907
Reviewed-by: John Stiles <johnstiles@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>

gn/sksl.gni

@@ -29,6 +29,7 @@ skia_sksl_sources = [
   "$_include/sksl/DSLModifiers.h",
   "$_include/sksl/DSLRuntimeEffects.h",
   "$_include/sksl/DSLStatement.h",
+  "$_include/sksl/DSLSymbols.h",
   "$_include/sksl/DSLType.h",
   "$_include/sksl/DSLVar.h",
   "$_src/sksl/SkSLASTFile.h",
@@ -86,6 +87,7 @@ skia_sksl_sources = [
   "$_src/sksl/dsl/DSLLayout.cpp",
   "$_src/sksl/dsl/DSLRuntimeEffects.cpp",
   "$_src/sksl/dsl/DSLStatement.cpp",
+  "$_src/sksl/dsl/DSLSymbols.cpp",
   "$_src/sksl/dsl/DSLType.cpp",
   "$_src/sksl/dsl/DSLVar.cpp",
   "$_src/sksl/dsl/priv/DSLFPs.cpp",

include/sksl/DSLSymbols.h

@@ -0,0 +1,72 @@
+/*
+ * Copyright 2021 Google LLC
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SKSL_DSL_SYMBOLS
+#define SKSL_DSL_SYMBOLS
+
+#include "include/core/SkStringView.h"
+#include "include/private/SkSLString.h"
+#include "include/sksl/DSLExpression.h"
+
+#include <memory>
+
+namespace SkSL {
+
+class SymbolTable;
+
+namespace dsl {
+
+class DSLVar;
+
+// This header provides methods for manually managing symbol tables in DSL code. They should not be
+// used by normal hand-written DSL code, where we rely on C++ to manage symbols, but are instead
+// needed when DSL objects are being constructed programmatically (as in DSLParser).
+
+/**
+ * Pushes a new symbol table onto the symbol table stack.
+ */
+void PushSymbolTable();
+
+/**
+ * Pops the top symbol table from the stack. As symbol tables are shared pointers, this will only
+ * destroy the symbol table if it was never attached to anything (e.g. passed into a Block
+ * constructor).
+ */
+void PopSymbolTable();
+
+/**
+ * Returns the current symbol table. Outside of SkSL itself, this is an opaque pointer, used only
+ * for passing it to DSL methods that require it.
+ */
+std::shared_ptr<SymbolTable> CurrentSymbolTable();
+
+/**
+ * Returns an expression referring to the named symbol.
+ */
+DSLExpression Symbol(skstd::string_view name);
+
+/**
+ * Returns true if the name refers to a type.
+ */
+bool IsType(skstd::string_view name);
+
+/**
+ * Adds a variable to the current symbol table.
+ */
+void AddToSymbolTable(DSLVar& var);
+
+/**
+ * Attaches a String to the current symbol table. The String will persist as long as the symbol
+ * table remains in memory.
+ */
+const String* Retain(String s);
+
+} // namespace dsl
+
+} // namespace SkSL
+
+#endif

src/sksl/dsl/DSLSymbols.cpp

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2021 Google LLC.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "include/sksl/DSLSymbols.h"
+
+#include "src/sksl/SkSLIRGenerator.h"
+#include "src/sksl/dsl/priv/DSLWriter.h"
+
+namespace SkSL {
+
+namespace dsl {
+
+void PushSymbolTable() {
+    DSLWriter::IRGenerator().pushSymbolTable();
+}
+
+void PopSymbolTable() {
+    DSLWriter::IRGenerator().popSymbolTable();
+}
+
+std::shared_ptr<SymbolTable> CurrentSymbolTable() {
+    return DSLWriter::IRGenerator().symbolTable();
+}
+
+DSLExpression Symbol(skstd::string_view name) {
+    return DSLWriter::IRGenerator().convertIdentifier(/*offset=*/-1, name);
+}
+
+bool IsType(skstd::string_view name) {
+    const SkSL::Symbol* s = (*CurrentSymbolTable())[name];
+    return s && s->is<Type>();
+}
+
+void AddToSymbolTable(DSLVar& var) {
+    CurrentSymbolTable()->addWithoutOwnership(&DSLWriter::Var(var));
+}
+
+const String* Retain(String string) {
+    return CurrentSymbolTable()->takeOwnershipOfString(std::move(string));
+}
+
+} // namespace dsl
+
+} // namespace SkSL