Improve parsing of incomplete field accesses in preparation for field completion

We need to be able to get the receiver even if there is no field name yet, and
currently "a." wouldn't get parsed as a field name at all. This seems to help.

3 files changed, 45 insertions, 9 deletions

diff --git a/crates/ra_syntax/src/grammar/expressions.rs b/crates/ra_syntax/src/grammar/expressions.rs
index da78d85a2..2d1f17491 100644
--- a/crates/ra_syntax/src/grammar/expressions.rs
+++ b/crates/ra_syntax/src/grammar/expressions.rs
@@ -283,14 +283,10 @@ fn postfix_expr(
             // }
             L_PAREN if allow_calls => call_expr(p, lhs),
             L_BRACK if allow_calls => index_expr(p, lhs),
-            DOT if p.nth(1) == IDENT => {
-                if p.nth(2) == L_PAREN || p.nth(2) == COLONCOLON {
-                    method_call_expr(p, lhs)
-                } else {
-                    field_expr(p, lhs)
-                }
+            DOT if p.nth(1) == IDENT && (p.nth(2) == L_PAREN || p.nth(2) == COLONCOLON) => {
+                method_call_expr(p, lhs)
             }
-            DOT if p.nth(1) == INT_NUMBER => field_expr(p, lhs),
+            DOT => field_expr(p, lhs),
             // test postfix_range
             // fn foo() { let x = 1..; }
             DOTDOT | DOTDOTEQ if !EXPR_FIRST.contains(p.nth(1)) => {
@@ -355,13 +351,15 @@ fn method_call_expr(p: &mut Parser, lhs: CompletedMarker) -> CompletedMarker {
 //     x.0.bar;
 // }
 fn field_expr(p: &mut Parser, lhs: CompletedMarker) -> CompletedMarker {
-    assert!(p.at(DOT) && (p.nth(1) == IDENT || p.nth(1) == INT_NUMBER));
+    assert!(p.at(DOT));
     let m = lhs.precede(p);
     p.bump();
     if p.at(IDENT) {
         name_ref(p)
-    } else {
+    } else if p.at(INT_NUMBER) {
         p.bump()
+    } else {
+        p.error("expected field name or number")
     }
     m.complete(p, FIELD_EXPR)
 }
diff --git a/crates/ra_syntax/tests/data/parser/err/0029_field_completion.rs b/crates/ra_syntax/tests/data/parser/err/0029_field_completion.rs
new file mode 100644
index 000000000..a7cdc17bb
--- /dev/null
+++ b/crates/ra_syntax/tests/data/parser/err/0029_field_completion.rs
@@ -0,0 +1,3 @@
+fn foo(a: A) {
+    a.
+}
diff --git a/crates/ra_syntax/tests/data/parser/err/0029_field_completion.txt b/crates/ra_syntax/tests/data/parser/err/0029_field_completion.txt
new file mode 100644
index 000000000..fd2a3f37b
--- /dev/null
+++ b/crates/ra_syntax/tests/data/parser/err/0029_field_completion.txt
@@ -0,0 +1,35 @@
+SOURCE_FILE@[0; 24)
+  FN_DEF@[0; 23)
+    FN_KW@[0; 2)
+    WHITESPACE@[2; 3)
+    NAME@[3; 6)
+      IDENT@[3; 6) "foo"
+    PARAM_LIST@[6; 12)
+      L_PAREN@[6; 7)
+      PARAM@[7; 11)
+        BIND_PAT@[7; 8)
+          NAME@[7; 8)
+            IDENT@[7; 8) "a"
+        COLON@[8; 9)
+        WHITESPACE@[9; 10)
+        PATH_TYPE@[10; 11)
+          PATH@[10; 11)
+            PATH_SEGMENT@[10; 11)
+              NAME_REF@[10; 11)
+                IDENT@[10; 11) "A"
+      R_PAREN@[11; 12)
+    WHITESPACE@[12; 13)
+    BLOCK@[13; 23)
+      L_CURLY@[13; 14)
+      WHITESPACE@[14; 19)
+      FIELD_EXPR@[19; 21)
+        PATH_EXPR@[19; 20)
+          PATH@[19; 20)
+            PATH_SEGMENT@[19; 20)
+              NAME_REF@[19; 20)
+                IDENT@[19; 20) "a"
+        DOT@[20; 21)
+        err: `expected field name or number`
+      WHITESPACE@[21; 22)
+      R_CURLY@[22; 23)
+  WHITESPACE@[23; 24)