Rename -Z explain to -Z teach

Author: estebank

Diff for: src/librustc/session/config.rs

@@ -1122,7 +1122,7 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
           "treat all errors that occur as bugs"),
     external_macro_backtrace: bool = (false, parse_bool, [UNTRACKED],
           "show macro backtraces even for non-local macros"),
-    explain: bool = (false, parse_bool, [TRACKED],
+    teach: bool = (false, parse_bool, [TRACKED],
           "show extended diagnostic help"),
     continue_parse_after_error: bool = (false, parse_bool, [TRACKED],
           "attempt to recover from parse errors (experimental)"),

Diff for: src/librustc/session/mod.rs

@@ -832,8 +832,8 @@ impl Session {
         }
     }
 
-    pub fn explain(&self, code: &DiagnosticId) -> bool {
-        self.opts.debugging_opts.explain && !self.parse_sess.span_diagnostic.code_emitted(code)
+    pub fn teach(&self, code: &DiagnosticId) -> bool {
+        self.opts.debugging_opts.teach && !self.parse_sess.span_diagnostic.code_emitted(code)
     }
 }
 

Diff for: src/librustc_typeck/structured_errors.rs

@@ -22,7 +22,7 @@ pub trait StructuredDiagnostic<'tcx> {
 
     fn diagnostic(&self) -> DiagnosticBuilder<'tcx> {
         let err = self.common();
-        if self.session().explain(&self.code()) {
+        if self.session().teach(&self.code()) {
             self.extended(err)
         } else {
             self.regular(err)