Detect long types in E0308 and write them to disk

On type error with long types, print an abridged type and write the full
type to disk.

Print the widest possible short type while still fitting in the
terminal.

2 files changed, 12 insertions, 0 deletions

diff --git a/compiler/rustc_session/Cargo.toml b/compiler/rustc_session/Cargo.toml
index a052f293341..cbbba2252bf 100644
--- a/compiler/rustc_session/Cargo.toml
+++ b/compiler/rustc_session/Cargo.toml
@@ -18,6 +18,7 @@ rustc_fs_util = { path = "../rustc_fs_util" }
 rustc_ast = { path = "../rustc_ast" }
 rustc_lint_defs = { path = "../rustc_lint_defs" }
 smallvec = "1.8.1"
+termize = "0.1.1"
 
 [target.'cfg(unix)'.dependencies]
 libc = "0.2"
diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
index e99e460913e..4c049a8d628 100644
--- a/compiler/rustc_session/src/session.rs
+++ b/compiler/rustc_session/src/session.rs
@@ -952,6 +952,17 @@ impl Session {
     ) -> Option<Symbol> {
         attrs.iter().find(|at| at.has_name(name)).and_then(|at| at.value_str())
     }
+
+    pub fn diagnostic_width(&self) -> usize {
+        let default_column_width = 140;
+        if let Some(width) = self.opts.diagnostic_width {
+            width
+        } else if self.opts.unstable_opts.ui_testing {
+            default_column_width
+        } else {
+            termize::dimensions().map_or(default_column_width, |(w, _)| w)
+        }
+    }
 }
 
 // JUSTIFICATION: defn of the suggested wrapper fns