From b2bcb7229a4bce0c9459807552d071eb2b2c9a0e Mon Sep 17 00:00:00 2001
From: Phil Dawes <phil@phildawes.net>
Date: Sat, 28 Mar 2015 21:58:51 +0000
Subject: Work towards a non-panicing parser (libsyntax)

- Functions in parser.rs return PResult<> rather than panicing
- Other functions in libsyntax call panic! explicitly for now if they rely on panicing behaviour.
- 'panictry!' macro added as scaffolding while converting panicing functions.
  (This does the same as 'unwrap()' but is easier to grep for and turn into try!())
- Leaves panicing wrappers for the following functions so that the
  quote_* macros behave the same:
  - parse_expr, parse_item, parse_pat, parse_arm, parse_ty, parse_stmt
---
 src/libsyntax/ext/format.rs | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

(limited to 'src/libsyntax/ext/format.rs')

diff --git a/src/libsyntax/ext/format.rs b/src/libsyntax/ext/format.rs
index 2fe77bf7a54..fe3a05cfc44 100644
--- a/src/libsyntax/ext/format.rs
+++ b/src/libsyntax/ext/format.rs
@@ -24,6 +24,17 @@ use ptr::P;
 use std::collections::HashMap;
 use std::iter::repeat;
 
+macro_rules! panictry {
+    ($e:expr) => ({
+        use std::result::Result::{Ok, Err};
+
+        match $e {
+            Ok(e) => e,
+            Err(e) => { panic!(e); }
+        }
+    })
+}
+
 #[derive(PartialEq)]
 enum ArgumentType {
     Known(String),
@@ -92,7 +103,7 @@ fn parse_args(ecx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
     let fmtstr = p.parse_expr();
     let mut named = false;
     while p.token != token::Eof {
-        if !p.eat(&token::Comma) {
+        if !panictry!(p.eat(&token::Comma)) {
             ecx.span_err(sp, "expected token: `,`");
             return None;
         }
@@ -101,7 +112,7 @@ fn parse_args(ecx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
             named = true;
             let ident = match p.token {
                 token::Ident(i, _) => {
-                    p.bump();
+                    panictry!(p.bump());
                     i
                 }
                 _ if named => {
@@ -120,7 +131,7 @@ fn parse_args(ecx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
             let interned_name = token::get_ident(ident);
             let name = &interned_name[..];
 
-            p.expect(&token::Eq);
+            panictry!(p.expect(&token::Eq));
             let e = p.parse_expr();
             match names.get(name) {
                 None => {}
-- 
cgit 1.4.1-3-g733a5


From e3427c3c341fcd15cbac783bf8dad7276422c97a Mon Sep 17 00:00:00 2001
From: Phil Dawes <phil@phildawes.net>
Date: Sat, 4 Apr 2015 21:47:40 +0100
Subject: Add comments suggested by Niko

---
 src/libsyntax/diagnostic.rs |  6 +++---
 src/libsyntax/ext/asm.rs    | 11 -----------
 src/libsyntax/ext/format.rs | 11 -----------
 src/libsyntax/lib.rs        |  8 ++++++--
 4 files changed, 9 insertions(+), 27 deletions(-)

(limited to 'src/libsyntax/ext/format.rs')

diff --git a/src/libsyntax/diagnostic.rs b/src/libsyntax/diagnostic.rs
index c746445e77e..8fe23a3c8e8 100644
--- a/src/libsyntax/diagnostic.rs
+++ b/src/libsyntax/diagnostic.rs
@@ -68,9 +68,9 @@ pub trait Emitter {
                    sp: RenderSpan, msg: &str, lvl: Level);
 }
 
-/// This structure is used to signify that a task has panicked with a fatal error
-/// from the diagnostics. You can use this with the `Any` trait to figure out
-/// how a rustc task died (if so desired).
+/// Used as a return value to signify a fatal error occurred. (It is also
+/// used as the argument to panic at the moment, but that will eventually
+/// not be true.)
 #[derive(Copy, Clone)]
 #[must_use]
 pub struct FatalError;
diff --git a/src/libsyntax/ext/asm.rs b/src/libsyntax/ext/asm.rs
index 3513f6d2bb9..f2b45d89f73 100644
--- a/src/libsyntax/ext/asm.rs
+++ b/src/libsyntax/ext/asm.rs
@@ -23,17 +23,6 @@ use parse::token::InternedString;
 use parse::token;
 use ptr::P;
 
-macro_rules! panictry {
-    ($e:expr) => ({
-        use std::result::Result::{Ok, Err};
-
-        match $e {
-            Ok(e) => e,
-            Err(e) => panic!(e),
-        }
-    })
-}
-
 enum State {
     Asm,
     Outputs,
diff --git a/src/libsyntax/ext/format.rs b/src/libsyntax/ext/format.rs
index fe3a05cfc44..1d99a475b32 100644
--- a/src/libsyntax/ext/format.rs
+++ b/src/libsyntax/ext/format.rs
@@ -24,17 +24,6 @@ use ptr::P;
 use std::collections::HashMap;
 use std::iter::repeat;
 
-macro_rules! panictry {
-    ($e:expr) => ({
-        use std::result::Result::{Ok, Err};
-
-        match $e {
-            Ok(e) => e,
-            Err(e) => { panic!(e); }
-        }
-    })
-}
-
 #[derive(PartialEq)]
 enum ArgumentType {
     Known(String),
diff --git a/src/libsyntax/lib.rs b/src/libsyntax/lib.rs
index a8b6dae06b9..bf95daf8755 100644
--- a/src/libsyntax/lib.rs
+++ b/src/libsyntax/lib.rs
@@ -50,13 +50,17 @@ extern crate libc;
 
 extern crate serialize as rustc_serialize; // used by deriving
 
+// A variant of 'try!' that panics on Err(FatalError). This is used as a
+// crutch on the way towards a non-panic!-prone parser. It should be used
+// for fatal parsing errors; eventually we plan to convert all code using
+// panictry to just use normal try
 macro_rules! panictry {
     ($e:expr) => ({
         use std::result::Result::{Ok, Err};
-
+        use diagnostic::FatalError;
         match $e {
             Ok(e) => e,
-            Err(e) => panic!(e)
+            Err(FatalError) => panic!(FatalError)
         }
     })
 }
-- 
cgit 1.4.1-3-g733a5