Add 'Span::len()' and 'Span::trimmed()' proc-macro methods.

src/libproc_macro/lib.rs

@@ -59,7 +59,7 @@ use syntax::errors::DiagnosticBuilder;
 use syntax::parse::{self, token};
 use syntax::symbol::Symbol;
 use syntax::tokenstream::{self, DelimSpan};
-use syntax_pos::{Pos, FileName};
+use syntax_pos::{Pos, BytePos, FileName};
 
 /// The main type provided by this crate, representing an abstract stream of
 /// tokens, or, more specifically, a sequence of token trees.
@@ -282,6 +282,12 @@ macro_rules! diagnostic_method {
 }
 
 impl Span {
+    /// Returns the length, in bytes of the span.
+    #[unstable(feature = "proc_macro_span", issue = "38356")]
+    pub fn len(&self) -> usize {
+        self.0.hi().to_usize() - self.0.lo().to_usize()
+    }
+
     /// A span that resolves at the macro definition site.
     #[unstable(feature = "proc_macro_span", issue = "38356")]
     pub fn def_site() -> Span {
@@ -353,6 +359,38 @@ impl Span {
         Some(Span(self.0.to(other.0)))
     }
 
+    /// Creates a new span by trimming `self` on the left by `left` bytes and on
+    /// the right by `right` bytes. Returns `None` if the would-be trimmed span
+    /// is outside the bounds of `self`.
+    #[unstable(feature = "proc_macro_span", issue = "38356")]
+    pub fn trimmed(&self, left: usize, right: usize) -> Option<Span> {
+        if left > u32::max_value() as usize || right > u32::max_value() as usize {
+            return None;
+        }
+
+        // Ensure that the addition won't overflow.
+        let (inner, left, right) = (self.0, left as u32, right as u32);
+        if u32::max_value() - left < inner.lo().to_u32() {
+            return None;
+        }
+
+        // Ensure that the subtraction won't underflow.
+        if right > inner.hi().to_u32() {
+            return None;
+        }
+
+        // Compute the new lo and hi.
+        let new_lo = inner.lo() + BytePos::from_u32(left);
+        let new_hi = inner.hi() - BytePos::from_u32(right);
+
+        // Ensure we're still inside the old `Span` and didn't cross paths.
+        if new_lo >= new_hi {
+            return None;
+        }
+
+        Some(Span(inner.with_lo(new_lo).with_hi(new_hi)))
+    }
+
     /// Creates a new span with the same line/column information as `self` but
     /// that resolves symbols as though it were at `other`.
     #[unstable(feature = "proc_macro_span", issue = "38356")]

src/test/ui-fulldeps/proc-macro/auxiliary/trimmed-span.rs

@@ -0,0 +1,48 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// no-prefer-dynamic
+
+#![crate_type = "proc-macro"]
+#![feature(proc_macro_diagnostic, proc_macro_span)]
+
+extern crate proc_macro;
+
+use proc_macro::{TokenStream, TokenTree, Span, Diagnostic};
+
+fn parse(input: TokenStream) -> Result<(), Diagnostic> {
+    if let Some(TokenTree::Literal(lit)) = input.into_iter().next() {
+        let mut spans = vec![];
+        let string = lit.to_string();
+        for hi in string.matches("hi") {
+            let index = hi.as_ptr() as usize - string.as_ptr() as usize;
+            let remaining = string.len() - (index + 2);
+            let sub_span = lit.span().trimmed(index, remaining).unwrap();
+            spans.push(sub_span);
+        }
+
+        if !spans.is_empty() {
+            Err(Span::call_site().error("found 'hi's").span_note(spans, "here"))
+        } else {
+            Ok(())
+        }
+    } else {
+        Err(Span::call_site().error("invalid input: expected string literal"))
+    }
+}
+
+#[proc_macro]
+pub fn trimmed(input: TokenStream) -> TokenStream {
+    if let Err(diag) = parse(input) {
+        diag.emit();
+    }
+
+    TokenStream::new()
+}

src/test/ui-fulldeps/proc-macro/trimmed-span.rs

@@ -0,0 +1,39 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// aux-build:trimmed-span.rs
+// ignore-stage1
+
+#![feature(proc_macro_non_items)]
+
+extern crate trimmed_span;
+
+use trimmed_span::trimmed;
+
+fn main() {
+    // This one emits no error.
+    trimmed!("");
+
+    // Exactly one 'hi'.
+    trimmed!("hi"); //~ ERROR found 'hi's
+
+    // Now two, back to back.
+    trimmed!("hihi"); //~ ERROR found 'hi's
+
+    // Now three, back to back.
+    trimmed!("hihihi"); //~ ERROR found 'hi's
+
+    // Now several, with spacing.
+    trimmed!("why I hide? hi!"); //~ ERROR found 'hi's
+    trimmed!("hey, hi, hidy, hidy, hi hi"); //~ ERROR found 'hi's
+    trimmed!("this is a hi, and this is another hi"); //~ ERROR found 'hi's
+    trimmed!("how are you this evening"); //~ ERROR found 'hi's
+    trimmed!("this is highly eradic"); //~ ERROR found 'hi's
+}

src/test/ui-fulldeps/proc-macro/trimmed-span.stderr

@@ -0,0 +1,98 @@
+error: found 'hi's
+  --> $DIR/trimmed-span.rs:25:5
+   |
+LL |     trimmed!("hi"); //~ ERROR found 'hi's
+   |     ^^^^^^^^^^^^^^^
+   |
+note: here
+  --> $DIR/trimmed-span.rs:25:15
+   |
+LL |     trimmed!("hi"); //~ ERROR found 'hi's
+   |               ^^
+
+error: found 'hi's
+  --> $DIR/trimmed-span.rs:28:5
+   |
+LL |     trimmed!("hihi"); //~ ERROR found 'hi's
+   |     ^^^^^^^^^^^^^^^^^
+   |
+note: here
+  --> $DIR/trimmed-span.rs:28:15
+   |
+LL |     trimmed!("hihi"); //~ ERROR found 'hi's
+   |               ^^^^
+
+error: found 'hi's
+  --> $DIR/trimmed-span.rs:31:5
+   |
+LL |     trimmed!("hihihi"); //~ ERROR found 'hi's
+   |     ^^^^^^^^^^^^^^^^^^^
+   |
+note: here
+  --> $DIR/trimmed-span.rs:31:15
+   |
+LL |     trimmed!("hihihi"); //~ ERROR found 'hi's
+   |               ^^^^^^
+
+error: found 'hi's
+  --> $DIR/trimmed-span.rs:34:5
+   |
+LL |     trimmed!("why I hide? hi!"); //~ ERROR found 'hi's
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: here
+  --> $DIR/trimmed-span.rs:34:21
+   |
+LL |     trimmed!("why I hide? hi!"); //~ ERROR found 'hi's
+   |                     ^^    ^^
+
+error: found 'hi's
+  --> $DIR/trimmed-span.rs:35:5
+   |
+LL |     trimmed!("hey, hi, hidy, hidy, hi hi"); //~ ERROR found 'hi's
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: here
+  --> $DIR/trimmed-span.rs:35:20
+   |
+LL |     trimmed!("hey, hi, hidy, hidy, hi hi"); //~ ERROR found 'hi's
+   |                    ^^  ^^    ^^    ^^ ^^
+
+error: found 'hi's
+  --> $DIR/trimmed-span.rs:36:5
+   |
+LL |     trimmed!("this is a hi, and this is another hi"); //~ ERROR found 'hi's
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: here
+  --> $DIR/trimmed-span.rs:36:16
+   |
+LL |     trimmed!("this is a hi, and this is another hi"); //~ ERROR found 'hi's
+   |                ^^       ^^       ^^             ^^
+
+error: found 'hi's
+  --> $DIR/trimmed-span.rs:37:5
+   |
+LL |     trimmed!("how are you this evening"); //~ ERROR found 'hi's
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: here
+  --> $DIR/trimmed-span.rs:37:28
+   |
+LL |     trimmed!("how are you this evening"); //~ ERROR found 'hi's
+   |                            ^^
+
+error: found 'hi's
+  --> $DIR/trimmed-span.rs:38:5
+   |
+LL |     trimmed!("this is highly eradic"); //~ ERROR found 'hi's
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: here
+  --> $DIR/trimmed-span.rs:38:16
+   |
+LL |     trimmed!("this is highly eradic"); //~ ERROR found 'hi's
+   |                ^^     ^^
+
+error: aborting due to 8 previous errors
+