propagate intersection of static info from if and cond branches

rhombus/private/cond.rkt

@@ -5,6 +5,7 @@
          "expression.rkt"
          "parse.rkt"
          "else-clause.rkt"
+         "static-info.rkt"
          "parens.rkt"
          "realm.rkt")
 
@@ -21,12 +22,17 @@
         (syntax-parse #'(alt ...)
           [((tag-thn::block thn ...)
             (tag-els::block els ...))
+           (define thn-e (enforest-expression-block #'(tag-thn thn ...)))
+           (define els-e (enforest-expression-block #'(tag-els els ...)))
            (values
-            (relocate+reraw
-             (respan stx)
-             #'(if (rhombus-expression (group test ...))
-                   (rhombus-body-at tag-thn thn ...)
-                   (rhombus-body-at tag-els els ...)))
+            (wrap-static-info*
+             (relocate+reraw
+              (respan stx)
+              #`(if (rhombus-expression (group test ...))
+                    #,(discard-static-infos thn-e)
+                    #,(discard-static-infos els-e)))
+             (static-infos-intersect (extract-static-infos thn-e)
+                                     (extract-static-infos els-e)))
             #'())]
           [_
            (raise-syntax-error #f
@@ -42,26 +48,43 @@
                   (_::block (group pred ... (tag::block rhs ...)))
                   ...
                   e::else-clause))
+        (define rhs-es (map enforest-expression-block
+                            (syntax->list #'((tag rhs ...) ...))))
+        (define els-e (syntax-parse #'e.parsed
+                        #:literals (rhombus-body-at)
+                        [(rhombus-body-at tag else-rhs ...)
+                         (enforest-expression-block #'(tag else-rhs ...))]
+                        [(rhombus-expression g)
+                         (enforest-expression-block #'g)]
+                        [_ #'e.parsed]))
         (values
-         (relocate+reraw
-          (respan stx)
-          #'(cond
-              [(rhombus-expression (group pred ...))
-               (rhombus-body-at tag rhs ...)]
-              ...
-              [else e.parsed]))
+         (with-syntax ([(rhs ...) (map discard-static-infos rhs-es)])
+           (wrap-static-info*
+            (relocate+reraw
+             (respan stx)
+             #`(cond
+                 [(rhombus-expression (group pred ...)) rhs]
+                 ...
+                 [else #,(discard-static-infos els-e)]))
+            (for/fold ([si (extract-static-infos els-e)]) ([rhs-e (in-list rhs-es)])
+              (static-infos-intersect si (extract-static-infos rhs-e)))))
          #'())]
        [(form-id (_::alts
                   (_::block (group pred ... (tag::block rhs ...)))
                   ...))
+        (define rhs-es (map enforest-expression-block
+                            (syntax->list #'((tag rhs ...) ...))))
         (values
-         (relocate+reraw
-          (respan stx)
-          #'(cond
-              [(rhombus-expression (group pred ...))
-               (rhombus-body-at tag rhs ...)]
-              ...
-              [else (cond-fallthrough 'form-id)]))
+         (with-syntax ([(rhs ...) (map discard-static-infos rhs-es)])
+           (wrap-static-info*
+            (relocate+reraw
+             (respan stx)
+             #'(cond
+                 [(rhombus-expression (group pred ...)) rhs]
+                 ...
+                 [else (cond-fallthrough 'form-id)]))
+            (for/fold ([si (extract-static-infos (car rhs-es))]) ([rhs-e (in-list (cdr rhs-es))])
+              (static-infos-intersect si (extract-static-infos rhs-e)))))
          #'())]
        [(form-id (_::block))
         (values

rhombus/scribblings/ref-cond.scrbl

@@ -21,6 +21,12 @@
  @rhombus(#false)), returns the result of the @rhombus(then_body) clause,
  otherwise returns the result of the @rhombus(else_body) clause.
 
+ Static information is gathered from @rhombus(then_body) and
+ @rhombus(else_body) under the same conditions as the right-hand side of
+ @rhombus(def) (see @secref("static-info-rules")), and the information is
+ intersected to determine the static information of the @rhombus(if)
+ form.
+
 @examples(
   if #true
   | "yes"
@@ -69,6 +75,13 @@
  If no @rhombus(clause_test_expr) produces a true value and there is no
  @rhombus(~else) clause, a run-time exception is thrown.
 
+ Static information is gathered from @rhombus(clause_result_body)s or
+ @rhombus(clause_result_expr) under the same conditions as the right-hand
+ side of @rhombus(def) (see @secref("static-info-rules")), and the
+ information is intersected to determine the static information of the
+ @rhombus(cond) form.
+
+
 }
 
 @doc(

rhombus/scribblings/ref-def.scrbl

@@ -27,10 +27,13 @@
  A @rhombus(bind) can be just an identifier or @rhombus(id_name), or it
  can be constructed with a binding operator, such as a pattern form or
  @rhombus(::) for annotations. The number of result values must match
- the number of @rhombus(bind)s.
+ the number of @rhombus(bind)s. Static information is gathered from
+ @rhombus(rhs_expr) or @rhombus(body) and propagated to
+ @rhombus(lhs_bind) as described in @secref("static-info-rules")).
 
- An identifier is bound in the @rhombus(expr, ~space) @tech{space}, and most
- binding operators also create bindings in the @rhombus(expr, ~space) space.
+ An identifier is bound in the @rhombus(expr, ~space) @tech{space}, and
+ most binding operators also create bindings in the
+ @rhombus(expr, ~space) space.
 
  When @rhombus(def) is used with @rhombus(=), then @rhombus(rhs_expr) must
  not contain any immediate @rhombus(=) terms (although @rhombus(=) can

rhombus/tests/cond.rhm

@@ -11,3 +11,52 @@ check:
   | #false: 17
   | ~else: 18
   ~is 18
+
+check:
+  use_static
+  (if #true | [1] | ["one"])[0]
+  ~is 1
+
+check:
+  ~eval
+  use_static
+  (if #true | [1] | "one")[0]
+  ~throws "specialization not known"
+
+check:
+  use_static
+  (cond | 1 == 2: [1] | 2 == 2: ["one"])[0]
+  ~is "one"
+
+check:
+  use_static
+  (cond | 1 == 2: [1] | ~else: ["one"])[0]
+  ~is "one"
+
+check:
+  use_static
+  (cond | 1 == 2: [1] | ~else ["one"])[0]
+  ~is "one"
+
+check:
+  ~eval
+  use_static
+  (if #true | [1] | "one")[0]
+  ~throws "specialization not known"
+
+check:
+  ~eval
+  use_static
+  (cond | #true: [1] | ~else: "one")[0]
+  ~throws "specialization not known"
+
+
+check:
+  ~eval
+  use_static
+  class Posn(x, y)
+  def p = (if #true
+           | Posn(1, 2)
+           | #void)
+  p.x
+  ~throws "no such field or method"