syntax::ext: replace span_fatal with span_err in many places.

This means that compilation continues for longer, and so we can see more
errors per compile. This is mildly more user-friendly because it stops
users having to run rustc n times to see n macro errors: just run it
once to see all of them.

Author: huonw

src/libsyntax/ext/asm.rs

@@ -59,9 +59,12 @@ pub fn expand_asm(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
     while continue_ {
         match state {
             Asm => {
-                let (s, style) =
-                    expr_to_str(cx, p.parse_expr(),
-                                "inline assembly must be a string literal.");
+                let (s, style) = match expr_to_str(cx, p.parse_expr(),
+                                                   "inline assembly must be a string literal.") {
+                    Some((s, st)) => (s, st),
+                    // let compilation continue
+                    None => return MacResult::dummy_expr(),
+                };
                 asm = s;
                 asm_str_style = Some(style);
             }

src/libsyntax/ext/base.rs

@@ -136,6 +136,17 @@ pub enum MacResult {
     MRAny(@AnyMacro),
     MRDef(MacroDef),
 }
+impl MacResult {
+    /// Create an empty expression MacResult; useful for satisfying
+    /// type signatures after emitting a non-fatal error (which stop
+    /// compilation well before the validity (or otherwise)) of the
+    /// expression are checked.
+    pub fn dummy_expr() -> MacResult {
+        MRExpr(@ast::Expr {
+                id: ast::DUMMY_NODE_ID, node: ast::ExprLogLevel, span: codemap::DUMMY_SP
+            })
+    }
+}
 
 pub enum SyntaxExtension {
     // #[deriving] and such
@@ -364,10 +375,27 @@ impl<'a> ExtCtxt<'a> {
             _ => self.bug("tried to pop without a push")
         }
     }
+    /// Emit `msg` attached to `sp`, and stop compilation immediately.
+    ///
+    /// `span_err` should be strongly prefered where-ever possible:
+    /// this should *only* be used when
+    /// - continuing has a high risk of flow-on errors (e.g. errors in
+    ///   declaring a macro would cause all uses of that macro to
+    ///   complain about "undefined macro"), or
+    /// - there is literally nothing else that can be done (however,
+    ///   in most cases one can construct a dummy expression/item to
+    ///   substitute; we never hit resolve/type-checking so the dummy
+    ///   value doesn't have to match anything)
     pub fn span_fatal(&self, sp: Span, msg: &str) -> ! {
         self.print_backtrace();
         self.parse_sess.span_diagnostic.span_fatal(sp, msg);
     }
+
+    /// Emit `msg` attached to `sp`, without immediately stopping
+    /// compilation.
+    ///
+    /// Compilation will be stopped in the near future (at the end of
+    /// the macro expansion phase).
     pub fn span_err(&self, sp: Span, msg: &str) {
         self.print_backtrace();
         self.parse_sess.span_diagnostic.span_err(sp, msg);
@@ -402,53 +430,69 @@ impl<'a> ExtCtxt<'a> {
     }
 }
 
-pub fn expr_to_str(cx: &ExtCtxt, expr: @ast::Expr, err_msg: &str) -> (@str, ast::StrStyle) {
+/// Extract a string literal from `expr`, emitting `err_msg` if `expr`
+/// is not a string literal. This does not stop compilation on error,
+/// merely emits a non-fatal error and returns None.
+pub fn expr_to_str(cx: &ExtCtxt, expr: @ast::Expr,
+                   err_msg: &str) -> Option<(@str, ast::StrStyle)> {
     match expr.node {
         ast::ExprLit(l) => match l.node {
-            ast::LitStr(s, style) => (s, style),
-            _ => cx.span_fatal(l.span, err_msg)
+            ast::LitStr(s, style) => return Some((s, style)),
+            _ => cx.span_err(l.span, err_msg)
         },
-        _ => cx.span_fatal(expr.span, err_msg)
+        _ => cx.span_err(expr.span, err_msg)
     }
+    None
 }
 
+/// Non-fatally assert that `tts` is empty. Note that this function
+/// returns even when `tts` is non-empty, macros that *need* to stop
+/// compilation should call
+/// `cx.parse_sess.span_diagnostic.abort_if_errors()` (this should be
+/// done as rarely as possible).
 pub fn check_zero_tts(cx: &ExtCtxt, sp: Span, tts: &[ast::TokenTree],
                       name: &str) {
     if tts.len() != 0 {
-        cx.span_fatal(sp, format!("{} takes no arguments", name));
+        cx.span_err(sp, format!("{} takes no arguments", name));
     }
 }
 
+/// Extract the string literal from the first token of `tts`. If this
+/// is not a string literal, emit an error and return None.
 pub fn get_single_str_from_tts(cx: &ExtCtxt,
                                sp: Span,
                                tts: &[ast::TokenTree],
                                name: &str)
-                               -> @str {
+                               -> Option<@str> {
     if tts.len() != 1 {
-        cx.span_fatal(sp, format!("{} takes 1 argument.", name));
-    }
-
-    match tts[0] {
-        ast::TTTok(_, token::LIT_STR(ident))
-        | ast::TTTok(_, token::LIT_STR_RAW(ident, _)) => cx.str_of(ident),
-        _ => cx.span_fatal(sp, format!("{} requires a string.", name)),
+        cx.span_err(sp, format!("{} takes 1 argument.", name));
+    } else {
+        match tts[0] {
+            ast::TTTok(_, token::LIT_STR(ident))
+                | ast::TTTok(_, token::LIT_STR_RAW(ident, _)) => return Some(cx.str_of(ident)),
+            _ => cx.span_err(sp, format!("{} requires a string.", name)),
+        }
     }
+    None
 }
 
+/// Extract comma-separated expressions from `tts`. If there is a
+/// parsing error, emit a non-fatal error and return None.
 pub fn get_exprs_from_tts(cx: &ExtCtxt,
                           sp: Span,
-                          tts: &[ast::TokenTree]) -> ~[@ast::Expr] {
+                          tts: &[ast::TokenTree]) -> Option<~[@ast::Expr]> {
     let mut p = parse::new_parser_from_tts(cx.parse_sess(),
                                            cx.cfg(),
                                            tts.to_owned());
     let mut es = ~[];
     while p.token != token::EOF {
         if es.len() != 0 && !p.eat(&token::COMMA) {
-            cx.span_fatal(sp, "expected token: `,`");
+            cx.span_err(sp, "expected token: `,`");
+            return None;
         }
         es.push(p.parse_expr());
     }
-    es
+    Some(es)
 }
 
 // in order to have some notion of scoping for macros,

src/libsyntax/ext/bytes.rs

@@ -20,7 +20,10 @@ use std::char;
 
 pub fn expand_syntax_ext(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree]) -> base::MacResult {
     // Gather all argument expressions
-    let exprs = get_exprs_from_tts(cx, sp, tts);
+    let exprs = match get_exprs_from_tts(cx, sp, tts) {
+        None => return MacResult::dummy_expr(),
+        Some(e) => e,
+    };
     let mut bytes = ~[];
 
     for expr in exprs.iter() {

src/libsyntax/ext/concat.rs

@@ -18,7 +18,10 @@ use ext::build::AstBuilder;
 pub fn expand_syntax_ext(cx: &mut base::ExtCtxt,
                          sp: codemap::Span,
                          tts: &[ast::TokenTree]) -> base::MacResult {
-    let es = base::get_exprs_from_tts(cx, sp, tts);
+    let es = match base::get_exprs_from_tts(cx, sp, tts) {
+        Some(e) => e,
+        None => return base::MacResult::dummy_expr()
+    };
     let mut accumulator = ~"";
     for e in es.move_iter() {
         let e = cx.expand_expr(e);

src/libsyntax/ext/concat_idents.rs

@@ -23,12 +23,18 @@ pub fn expand_syntax_ext(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
         if i & 1 == 1 {
             match *e {
                 ast::TTTok(_, token::COMMA) => (),
-                _ => cx.span_fatal(sp, "concat_idents! expecting comma.")
+                _ => {
+                    cx.span_err(sp, "concat_idents! expecting comma.");
+                    return MacResult::dummy_expr();
+                }
             }
         } else {
             match *e {
                 ast::TTTok(_, token::IDENT(ident,_)) => res_str.push_str(cx.str_of(ident)),
-                _ => cx.span_fatal(sp, "concat_idents! requires ident args.")
+                _ => {
+                    cx.span_err(sp, "concat_idents! requires ident args.");
+                    return MacResult::dummy_expr();
+                }
             }
         }
     }

src/libsyntax/ext/deriving/default.rs

@@ -70,8 +70,9 @@ fn default_substructure(cx: &ExtCtxt, span: Span, substr: &Substructure) -> @Exp
             }
         }
         StaticEnum(..) => {
-            cx.span_fatal(span, "`Default` cannot be derived for enums, \
-                                 only structs")
+            cx.span_err(span, "`Default` cannot be derived for enums, only structs");
+            // let compilation continue
+            cx.expr_uint(span, 0)
         }
         _ => cx.bug("Non-static method in `deriving(Default)`")
     };

src/libsyntax/ext/deriving/rand.rs

@@ -73,7 +73,9 @@ fn rand_substructure(cx: &ExtCtxt, span: Span, substr: &Substructure) -> @Expr {
         }
         StaticEnum(_, ref variants) => {
             if variants.is_empty() {
-                cx.span_fatal(span, "`Rand` cannot be derived for enums with no variants");
+                cx.span_err(span, "`Rand` cannot be derived for enums with no variants");
+                // let compilation continue
+                return cx.expr_uint(span, 0);
             }
 
             let variant_count = cx.expr_uint(span, variants.len());

src/libsyntax/ext/deriving/zero.rs

@@ -86,8 +86,9 @@ fn zero_substructure(cx: &ExtCtxt, span: Span, substr: &Substructure) -> @Expr {
             }
         }
         StaticEnum(..) => {
-            cx.span_fatal(span, "`Zero` cannot be derived for enums, \
-                                 only structs")
+            cx.span_err(span, "`Zero` cannot be derived for enums, only structs");
+            // let compilation continue
+            cx.expr_uint(span, 0)
         }
         _ => cx.bug("Non-static method in `deriving(Zero)`")
     };

src/libsyntax/ext/env.rs

@@ -24,7 +24,10 @@ use std::os;
 
 pub fn expand_option_env(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
     -> base::MacResult {
-    let var = get_single_str_from_tts(cx, sp, tts, "option_env!");
+    let var = match get_single_str_from_tts(cx, sp, tts, "option_env!") {
+        None => return MacResult::dummy_expr(),
+        Some(v) => v
+    };
 
     let e = match os::getenv(var) {
       None => quote_expr!(cx, ::std::option::None::<&'static str>),
@@ -35,24 +38,38 @@ pub fn expand_option_env(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
 
 pub fn expand_env(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
     -> base::MacResult {
-    let exprs = get_exprs_from_tts(cx, sp, tts);
-
-    if exprs.len() == 0 {
-        cx.span_fatal(sp, "env! takes 1 or 2 arguments");
-    }
+    let exprs = match get_exprs_from_tts(cx, sp, tts) {
+        Some([]) => {
+            cx.span_err(sp, "env! takes 1 or 2 arguments");
+            return MacResult::dummy_expr();
+        }
+        None => return MacResult::dummy_expr(),
+        Some(exprs) => exprs
+    };
 
-    let (var, _var_str_style) = expr_to_str(cx, exprs[0], "expected string literal");
+    let var = match expr_to_str(cx, exprs[0], "expected string literal") {
+        None => return MacResult::dummy_expr(),
+        Some((v, _style)) => v
+    };
     let msg = match exprs.len() {
         1 => format!("environment variable `{}` not defined", var).to_managed(),
         2 => {
-            let (s, _style) = expr_to_str(cx, exprs[1], "expected string literal");
-            s
+            match expr_to_str(cx, exprs[1], "expected string literal") {
+                None => return MacResult::dummy_expr(),
+                Some((s, _style)) => s
+            }
+        }
+        _ => {
+            cx.span_err(sp, "env! takes 1 or 2 arguments");
+            return MacResult::dummy_expr();
         }
-        _ => cx.span_fatal(sp, "env! takes 1 or 2 arguments")
     };
 
     let e = match os::getenv(var) {
-        None => cx.span_fatal(sp, msg),
+        None => {
+            cx.span_err(sp, msg);
+            cx.expr_uint(sp, 0)
+        }
         Some(s) => cx.expr_str(sp, s.to_managed())
     };
     MRExpr(e)