Rename -Zparse-only.

I was surprised to find that running with `-Zparse-only` only parses the
crate root file. Other files aren't parsed because that happens later
during expansion.

This commit renames the option and updates the help message to make this
clearer.

Author: nnethercote

compiler/rustc_driver_impl/src/lib.rs

@@ -425,7 +425,9 @@ fn run_compiler(
                 return early_exit();
             }
 
-            if sess.opts.unstable_opts.parse_only || sess.opts.unstable_opts.show_span.is_some() {
+            if sess.opts.unstable_opts.parse_crate_root_only
+                || sess.opts.unstable_opts.show_span.is_some()
+            {
                 return early_exit();
             }
 

compiler/rustc_interface/src/tests.rs

@@ -712,7 +712,7 @@ fn test_unstable_options_tracking_hash() {
     untracked!(no_analysis, true);
     untracked!(no_leak_check, true);
     untracked!(no_parallel_backend, true);
-    untracked!(parse_only, true);
+    untracked!(parse_crate_root_only, true);
     // `pre_link_arg` is omitted because it just forwards to `pre_link_args`.
     untracked!(pre_link_args, vec![String::from("abc"), String::from("def")]);
     untracked!(print_codegen_stats, true);

compiler/rustc_session/src/config.rs

@@ -1208,7 +1208,7 @@ impl Options {
 
     /// Returns `true` if there will be an output file generated.
     pub fn will_create_output_file(&self) -> bool {
-        !self.unstable_opts.parse_only && // The file is just being parsed
+        !self.unstable_opts.parse_crate_root_only && // The file is just being parsed
             self.unstable_opts.ls.is_empty() // The file is just being queried
     }
 
@@ -1864,7 +1864,7 @@ fn parse_output_types(
     matches: &getopts::Matches,
 ) -> OutputTypes {
     let mut output_types = BTreeMap::new();
-    if !unstable_opts.parse_only {
+    if !unstable_opts.parse_crate_root_only {
         for list in matches.opt_strs("emit") {
             for output_type in list.split(',') {
                 let (shorthand, path) = split_out_file_name(output_type);

compiler/rustc_session/src/options.rs

@@ -1937,8 +1937,9 @@ options! {
         "support compiling tests with panic=abort (default: no)"),
     panic_in_drop: PanicStrategy = (PanicStrategy::Unwind, parse_panic_strategy, [TRACKED],
         "panic strategy for panics in drops"),
-    parse_only: bool = (false, parse_bool, [UNTRACKED],
-        "parse only; do not compile, assemble, or link (default: no)"),
+    parse_crate_root_only: bool = (false, parse_bool, [UNTRACKED],
+        "parse the crate root file only; do not parse other files, compile, assemble, or link \
+        (default: no)"),
     patchable_function_entry: PatchableFunctionEntry = (PatchableFunctionEntry::default(), parse_patchable_function_entry, [TRACKED],
         "nop padding at function entry"),
     plt: Option<bool> = (None, parse_opt_bool, [TRACKED],

tests/ui/generic-associated-types/parse/in-trait-impl.rs

@@ -1,5 +1,5 @@
 //@ check-pass
-//@ compile-flags: -Z parse-only
+//@ compile-flags: -Z parse-crate-root-only
 
 impl<T> Baz for T where T: Foo {
     type Quux<'a> = <T as Foo>::Bar<'a, 'static>;

tests/ui/generic-associated-types/parse/in-trait.rs

@@ -1,5 +1,5 @@
 //@ check-pass
-//@ compile-flags: -Z parse-only
+//@ compile-flags: -Z parse-crate-root-only
 
 use std::ops::Deref;
 use std::fmt::Debug;

tests/ui/impl-trait/impl-trait-plus-priority.rs

@@ -1,4 +1,4 @@
-//@ compile-flags: -Z parse-only
+//@ compile-flags: -Z parse-crate-root-only
 
 fn f() -> impl A + {} // OK
 fn f() -> impl A + B {} // OK

tests/ui/parser/assoc/assoc-oddities-1.rs

@@ -1,4 +1,4 @@
-//@ compile-flags: -Z parse-only
+//@ compile-flags: -Z parse-crate-root-only
 
 fn main() {
     // following lines below parse and must not fail

tests/ui/parser/assoc/assoc-oddities-2.rs

@@ -1,4 +1,4 @@
-//@ compile-flags: -Z parse-only
+//@ compile-flags: -Z parse-crate-root-only
 
 fn main() {
     // see assoc-oddities-1 for explanation

tests/ui/parser/bounds-type.rs

@@ -1,4 +1,4 @@
-//@ compile-flags: -Z parse-only
+//@ compile-flags: -Z parse-crate-root-only
 //@ edition: 2021
 
 struct S<