syntax: Various labeled-break follow-up

JuliaLowering/src/desugaring.jl

@@ -4459,8 +4459,8 @@ function expand_forms_2(ctx::DesugaringContext, ex::SyntaxTree, docs=nothing)
             # Convert Symbol (from Expr conversion) to symbolic_label
             if label_kind == K"Symbol"
                 label = @ast ctx label label.name_val::K"symbolic_label"
-            elseif !(label_kind == K"Identifier" || label_kind == K"symbolic_label" ||
-                     is_contextual_keyword(label_kind))
+            elseif !(label_kind == K"Identifier" || label_kind == K"Placeholder" ||
+                     label_kind == K"symbolic_label" || is_contextual_keyword(label_kind))
                 throw(LoweringError(label, "Invalid break label: expected identifier"))
             end
             if nc == 2

JuliaLowering/src/linear_ir.jl

@@ -308,8 +308,16 @@ function emit_break(ctx, ex)
     name = ex[1].name_val
     target = get(ctx.break_targets, name, nothing)
     if isnothing(target)
-        ty = name == "loop_exit" ? "break" : "continue"
-        throw(LoweringError(ex, "$ty must be used inside a `while` or `for` loop"))
+        if name == "loop_exit"
+            throw(LoweringError(ex, "`break` must be used inside a `while` or `for` loop"))
+        elseif name == "loop_cont"
+            throw(LoweringError(ex, "`continue` must be used inside a `while` or `for` loop"))
+        elseif endswith(name, "#cont")
+            label = name[1:end-5]
+            throw(LoweringError(ex, "`continue $label` is not inside a `@label $label` loop"))
+        else
+            throw(LoweringError(ex, "`break $name` is not inside a `@label $name` block"))
+        end
     end
     # Handle valued break (break name val)
     if numchildren(ex) >= 2

JuliaLowering/test/branching_ir.jl

@@ -237,3 +237,20 @@ x = @label foo
 LoweringError:
 x = @label foo
 #          └─┘ ── misplaced label in value position
+
+########################################
+# Labeled block with underscore label and valued break
+@label _ begin
+    a
+    break _ 42
+    b
+end
+#---------------------
+1   (= slot₁/__result core.nothing)
+2   TestMod.a
+3   (= slot₁/__result 42)
+4   (goto label₇)
+5   TestMod.b
+6   (= slot₁/__result %₅)
+7   slot₁/__result
+8   (return %₇)

JuliaLowering/test/loops_ir.jl

@@ -119,15 +119,15 @@ break
 #---------------------
 LoweringError:
 break
-└───┘ ── break must be used inside a `while` or `for` loop
+└───┘ ── `break` must be used inside a `while` or `for` loop
 
 ########################################
 # Error: continue outside for/while
 continue
 #---------------------
 LoweringError:
 continue
-└──────┘ ── continue must be used inside a `while` or `for` loop
+└──────┘ ── `continue` must be used inside a `while` or `for` loop
 
 ########################################
 # Error: `outer` without outer local variable

src/julia-syntax.scm

@@ -5069,7 +5069,10 @@ f(x) = yt(x)
             ((break)
              (let ((labl (assq (cadr e) break-labels)))
                (if (not labl)
-                   (error "break or continue outside loop")
+                   (let ((name (cadr e)))
+                     (if (memq name '(loop-exit loop-cont))
+                         (error "break or continue outside loop")
+                         (error (string "`break " name "` not in a block with label `" name "`"))))
                    (begin
                      ;; Check if this is a valued break (break name val)
                      (if (length> e 2)