Move start_index out of TranslationResult and into the WasmRuntime.

This makes it more consistent with how all the rest of the content of
a wasm module is handled. And, now TranslationResult just has a Vec
of translated functions, which will make it easier to refactor further.

lib/wasm/src/module_translator.rs

@@ -2,9 +2,9 @@
 //! to deal with each part of it.
 use wasmparser::{ParserState, SectionCode, ParserInput, Parser, WasmDecoder, BinaryReaderError};
 use sections_translator::{SectionParsingError, parse_function_signatures, parse_import_section,
-                          parse_function_section, parse_export_section, parse_memory_section,
-                          parse_global_section, parse_table_section, parse_elements_section,
-                          parse_data_section};
+                          parse_function_section, parse_export_section, parse_start_section,
+                          parse_memory_section, parse_global_section, parse_table_section,
+                          parse_elements_section, parse_data_section};
 use translation_utils::FunctionIndex;
 use cretonne::ir::{Function, FunctionName};
 use func_translator::FuncTranslator;
@@ -16,11 +16,6 @@ use runtime::WasmRuntime;
 pub struct TranslationResult {
     /// The translated functions.
     pub functions: Vec<Function>,
-    /// When present, the index of the function defined as `start` of the module.
-    ///
-    /// Note that this is a WebAssembly function index and not an index into the `functions` vector
-    /// above. The imported functions are numbered before the local functions.
-    pub start_index: Option<FunctionIndex>,
 }
 
 /// Translate a sequence of bytes forming a valid Wasm binary into a list of valid Cretonne IL
@@ -42,7 +37,6 @@ pub fn translate_module(
     let mut exports: HashMap<FunctionIndex, String> = HashMap::new();
     let mut next_input = ParserInput::Default;
     let mut function_index: FunctionIndex = 0;
-    let mut start_index: Option<FunctionIndex> = None;
     loop {
         match *parser.read_with_input(next_input) {
             ParserState::BeginSection { code: SectionCode::Type, .. } => {
@@ -108,15 +102,11 @@ pub fn translate_module(
                 next_input = ParserInput::Default;
             }
             ParserState::BeginSection { code: SectionCode::Start, .. } => {
-                match *parser.read() {
-                    ParserState::StartSectionEntry(index) => {
-                        start_index = Some(index as FunctionIndex)
+                match parse_start_section(&mut parser, runtime) {
+                    Ok(()) => (),
+                    Err(SectionParsingError::WrongSectionContent(s)) => {
+                        return Err(format!("wrong content in the start section: {}", s))
                     }
-                    _ => return Err(String::from("wrong content in the start section")),
-                }
-                match *parser.read() {
-                    ParserState::EndSection => {}
-                    _ => return Err(String::from("wrong content in the start section")),
                 }
                 next_input = ParserInput::Default;
             }
@@ -136,12 +126,7 @@ pub fn translate_module(
             ParserState::EndSection => {
                 next_input = ParserInput::Default;
             }
-            ParserState::EndWasm => {
-                return Ok(TranslationResult {
-                    functions: Vec::new(),
-                    start_index: None,
-                })
-            }
+            ParserState::EndWasm => return Ok(TranslationResult { functions: Vec::new() }),
             ParserState::BeginSection { code: SectionCode::Data, .. } => {
                 match parse_data_section(&mut parser, runtime) {
                     Ok(()) => (),
@@ -188,12 +173,7 @@ pub fn translate_module(
                     }
                 }
             }
-            ParserState::EndWasm => {
-                return Ok(TranslationResult {
-                    functions: il_functions,
-                    start_index,
-                })
-            }
+            ParserState::EndWasm => return Ok(TranslationResult { functions: il_functions }),
             _ => (),
         }
     }

lib/wasm/src/runtime/dummy.rs

@@ -22,6 +22,9 @@ pub struct DummyRuntime {
 
     // Compilation setting flags.
     flags: settings::Flags,
+
+    // The start function.
+    start_func: Option<FunctionIndex>,
 }
 
 impl DummyRuntime {
@@ -38,6 +41,7 @@ impl DummyRuntime {
             func_types: Vec::new(),
             imported_funcs: Vec::new(),
             flags,
+            start_func: None,
         }
     }
 }
@@ -177,6 +181,11 @@ impl WasmRuntime for DummyRuntime {
         Ok(())
     }
 
+    fn declare_start_func(&mut self, func_index: FunctionIndex) {
+        debug_assert!(self.start_func.is_none());
+        self.start_func = Some(func_index);
+    }
+
     fn begin_translation(&mut self) {
         // We do nothing
     }

lib/wasm/src/runtime/spec.rs

@@ -189,6 +189,10 @@ pub trait WasmRuntime: FuncEnvironment {
         offset: usize,
         data: &[u8],
     ) -> Result<(), String>;
+
+    /// Declares a start function.
+    fn declare_start_func(&mut self, index: FunctionIndex);
+
     /// Call this function after having declared all the runtime elements but prior to the
     /// function body translation.
     fn begin_translation(&mut self);

lib/wasm/src/sections_translator.rs

@@ -154,6 +154,23 @@ pub fn parse_export_section(
     Ok(exports)
 }
 
+/// Retrieves the start function index from the start section
+pub fn parse_start_section(
+    parser: &mut Parser,
+    runtime: &mut WasmRuntime,
+) -> Result<(), SectionParsingError> {
+    loop {
+        match *parser.read() {
+            ParserState::StartSectionEntry(index) => {
+                runtime.declare_start_func(index as FunctionIndex);
+            }
+            ParserState::EndSection => break,
+            ref s => return Err(SectionParsingError::WrongSectionContent(format!("{:?}", s))),
+        };
+    }
+    Ok(())
+}
+
 /// Retrieves the size and maximum fields of memories from the memory section
 pub fn parse_memory_section(
     parser: &mut Parser,