Auto merge of #52319 - tinco:issue_12590, r=pnkfelix

Track whether module declarations are inline (fixes #12590)

To track whether module declarations are inline I added a field `inline: bool` to `ast::Mod`. The main use case is for pretty to know whether it should render the items associated with the module, but perhaps there are use cases for this information to not be forgotten in the AST.

7 files changed, 40 insertions, 12 deletions

diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index cd2efb4c747..9ed628e2ed3 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -1885,6 +1885,8 @@ pub struct Mod {
     /// to the last token in the external file.
     pub inner: Span,
     pub items: Vec<P<Item>>,
+    /// For `mod foo;` inline is false, for `mod foo { .. }` it is true.
+    pub inline: bool,
 }
 
 /// Foreign module declaration.
diff --git a/src/libsyntax/ext/build.rs b/src/libsyntax/ext/build.rs
index b1bed9602f3..6210003a40d 100644
--- a/src/libsyntax/ext/build.rs
+++ b/src/libsyntax/ext/build.rs
@@ -1101,6 +1101,7 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
             ast::ItemKind::Mod(ast::Mod {
                 inner: inner_span,
                 items,
+                inline: true
             })
         )
     }
diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index 87c53d16875..52322e98d46 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -303,6 +303,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                 krate.module = ast::Mod {
                     inner: orig_mod_span,
                     items: vec![],
+                    inline: true,
                 };
             },
             _ => unreachable!(),
diff --git a/src/libsyntax/fold.rs b/src/libsyntax/fold.rs
index 3e422f5af81..95a2298ca75 100644
--- a/src/libsyntax/fold.rs
+++ b/src/libsyntax/fold.rs
@@ -1044,10 +1044,11 @@ pub fn noop_fold_fn_header<T: Folder>(mut header: FnHeader, folder: &mut T) -> F
     header
 }
 
-pub fn noop_fold_mod<T: Folder>(Mod {inner, items}: Mod, folder: &mut T) -> Mod {
+pub fn noop_fold_mod<T: Folder>(Mod {inner, items, inline}: Mod, folder: &mut T) -> Mod {
     Mod {
         inner: folder.new_span(inner),
         items: items.move_flat_map(|x| folder.fold_item(x)),
+        inline: inline,
     }
 }
 
@@ -1077,6 +1078,7 @@ pub fn noop_fold_crate<T: Folder>(Crate {module, attrs, span}: Crate,
         None => (ast::Mod {
             inner: span,
             items: vec![],
+            inline: true,
         }, vec![], span)
     };
 
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index d6cbe47a66e..5571a18b596 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -6297,6 +6297,7 @@ impl<'a> Parser<'a> {
         Ok(ast::Mod {
             inner: inner_lo.to(hi),
             items,
+            inline: true
         })
     }
 
@@ -6334,6 +6335,7 @@ impl<'a> Parser<'a> {
                     self.submod_path(id, &outer_attrs, id_span)?;
                 let (module, mut attrs) =
                     self.eval_src_mod(path, directory_ownership, id.to_string(), id_span)?;
+                // Record that we fetched the mod from an external file
                 if warn {
                     let attr = Attribute {
                         id: attr::mk_attr_id(),
@@ -6346,9 +6348,13 @@ impl<'a> Parser<'a> {
                     attr::mark_known(&attr);
                     attrs.push(attr);
                 }
-                Ok((id, module, Some(attrs)))
+                Ok((id, ItemKind::Mod(module), Some(attrs)))
             } else {
-                let placeholder = ast::Mod { inner: syntax_pos::DUMMY_SP, items: Vec::new() };
+                let placeholder = ast::Mod {
+                    inner: syntax_pos::DUMMY_SP,
+                    items: Vec::new(),
+                    inline: false
+                };
                 Ok((id, ItemKind::Mod(placeholder), None))
             }
         } else {
@@ -6548,7 +6554,7 @@ impl<'a> Parser<'a> {
                     directory_ownership: DirectoryOwnership,
                     name: String,
                     id_sp: Span)
-                    -> PResult<'a, (ast::ItemKind, Vec<Attribute> )> {
+                    -> PResult<'a, (ast::Mod, Vec<Attribute> )> {
         let mut included_mod_stack = self.sess.included_mod_stack.borrow_mut();
         if let Some(i) = included_mod_stack.iter().position(|p| *p == path) {
             let mut err = String::from("circular modules: ");
@@ -6568,9 +6574,10 @@ impl<'a> Parser<'a> {
         p0.cfg_mods = self.cfg_mods;
         let mod_inner_lo = p0.span;
         let mod_attrs = p0.parse_inner_attributes()?;
-        let m0 = p0.parse_mod_items(&token::Eof, mod_inner_lo)?;
+        let mut m0 = p0.parse_mod_items(&token::Eof, mod_inner_lo)?;
+        m0.inline = false;
         self.sess.included_mod_stack.borrow_mut().pop();
-        Ok((ast::ItemKind::Mod(m0), mod_attrs))
+        Ok((m0, mod_attrs))
     }
 
     /// Parse a function declaration from a foreign module
diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index 85d29a5be89..f2acdb3f469 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -61,6 +61,7 @@ pub struct State<'a> {
     cur_cmnt: usize,
     boxes: Vec<pp::Breaks>,
     ann: &'a (dyn PpAnn+'a),
+    is_expanded: bool
 }
 
 fn rust_printer<'a>(writer: Box<dyn Write+'a>, ann: &'a dyn PpAnn) -> State<'a> {
@@ -72,6 +73,7 @@ fn rust_printer<'a>(writer: Box<dyn Write+'a>, ann: &'a dyn PpAnn) -> State<'a>
         cur_cmnt: 0,
         boxes: Vec::new(),
         ann,
+        is_expanded: false
     }
 }
 
@@ -133,14 +135,17 @@ impl<'a> State<'a> {
             // If the code is post expansion, don't use the table of
             // literals, since it doesn't correspond with the literals
             // in the AST anymore.
-            if is_expanded { None } else { Some(lits) })
+            if is_expanded { None } else { Some(lits) },
+            is_expanded
+        )
     }
 
     pub fn new(cm: &'a SourceMap,
                out: Box<dyn Write+'a>,
                ann: &'a dyn PpAnn,
                comments: Option<Vec<comments::Comment>>,
-               literals: Option<Vec<comments::Literal>>) -> State<'a> {
+               literals: Option<Vec<comments::Literal>>,
+               is_expanded: bool) -> State<'a> {
         State {
             s: pp::mk_printer(out, DEFAULT_COLUMNS),
             cm: Some(cm),
@@ -149,6 +154,7 @@ impl<'a> State<'a> {
             cur_cmnt: 0,
             boxes: Vec::new(),
             ann,
+            is_expanded: is_expanded
         }
     }
 }
@@ -1260,10 +1266,18 @@ impl<'a> State<'a> {
             ast::ItemKind::Mod(ref _mod) => {
                 self.head(&visibility_qualified(&item.vis, "mod"))?;
                 self.print_ident(item.ident)?;
-                self.nbsp()?;
-                self.bopen()?;
-                self.print_mod(_mod, &item.attrs)?;
-                self.bclose(item.span)?;
+
+                if _mod.inline || self.is_expanded {
+                    self.nbsp()?;
+                    self.bopen()?;
+                    self.print_mod(_mod, &item.attrs)?;
+                    self.bclose(item.span)?;
+                } else {
+                    self.s.word(";")?;
+                    self.end()?; // end inner head-block
+                    self.end()?; // end outer head-block
+                }
+
             }
             ast::ItemKind::ForeignMod(ref nmod) => {
                 self.head("extern")?;
diff --git a/src/libsyntax/test.rs b/src/libsyntax/test.rs
index 744e2e4a5fd..9f554a90afb 100644
--- a/src/libsyntax/test.rs
+++ b/src/libsyntax/test.rs
@@ -237,6 +237,7 @@ fn mk_reexport_mod(cx: &mut TestCtxt,
     })).collect();
 
     let reexport_mod = ast::Mod {
+        inline: true,
         inner: DUMMY_SP,
         items,
     };