[wasm] Implement AST printing into an ostream

src/wasm/ast-decoder.h

Index: src/wasm/ast-decoder.h
diff --git a/src/wasm/ast-decoder.h b/src/wasm/ast-decoder.h
index 9e96053a6ce035773fbe9f992e24d2f0e8430c35..1b322fd05bccd87a21fde4ed0ab14549b0f4b65c 100644
--- a/src/wasm/ast-decoder.h
+++ b/src/wasm/ast-decoder.h
@@ -5,6 +5,8 @@
 #ifndef V8_WASM_AST_DECODER_H_
 #define V8_WASM_AST_DECODER_H_
 
+#include <functional>
+
 #include "src/signature.h"
 #include "src/wasm/decoder.h"
 #include "src/wasm/wasm-opcodes.h"
@@ -211,6 +213,9 @@ struct FunctionBody {
   const byte* base;   // base of the module bytes, for error reporting
   const byte* start;  // start of the function body
   const byte* end;    // end of the function body
+  static FunctionBody ForTesting(const byte* start, const byte* end) {

[titzer, 2016/06/10 10:57:40]

Can you please move this out to the top level? (style guide recommends no
functions within structs).

[Clemens Hammacher, 2016/06/13 09:45:17]

Done.
Not sure though if style guide really advises against this. It sais for structs:
Methods should not provide behavior but should only be used to set up the data
members, e.g., constructor, destructor, Initialize(), Reset(), Validate().

+    return {nullptr, nullptr, start, start, end};
+  }
 };
 
 struct Tree;
@@ -222,7 +227,9 @@ TreeResult VerifyWasmCode(base::AccountingAllocator* allocator,
                           FunctionBody& body);
 TreeResult BuildTFGraph(base::AccountingAllocator* allocator,
                         TFBuilder* builder, FunctionBody& body);
-void PrintAst(base::AccountingAllocator* allocator, FunctionBody& body);
+bool PrintAst(base::AccountingAllocator* allocator, const FunctionBody& body,
+              std::ostream& os,
+              std::function<void(uint32_t)> instruction_callback = {});

[titzer, 2016/06/10 10:57:40]

There isn't a usecase for the instruction_callback function yet. (I assume there
is one in a CL based on this one).

Can we avoid a callback and instead return a map from byte index to line (since
that is what I assume this is being used for)?

[Clemens Hammacher, 2016/06/13 09:45:17]

Done.

 
 // A simplified form of AST printing, e.g. from a debugger.
 void PrintAstForDebugging(const byte* start, const byte* end);