From 2a6a8c64ade7f1281dbd6a1920cf46c5b78231ab Mon Sep 17 00:00:00 2001
From: Jack Firth <jackhfirth@gmail.com>
Date: Fri, 30 Aug 2024 22:56:04 -0700
Subject: [PATCH] Improve `always-throwing-if-to-when` rule

Now it can detect cases where either branch of the `if` expression always throws, instead of just cases where the true branch always throws.
---
 .../conditional-shortcuts-test.rkt            | 30 +++++++++++++++++++
 .../conditional-shortcuts.rkt                 | 23 ++++++++++----
 2 files changed, 48 insertions(+), 5 deletions(-)

diff --git a/default-recommendations/conditional-shortcuts-test.rkt b/default-recommendations/conditional-shortcuts-test.rkt
index 7c7212b..36a8d76 100644
--- a/default-recommendations/conditional-shortcuts-test.rkt
+++ b/default-recommendations/conditional-shortcuts-test.rkt
@@ -152,6 +152,21 @@ test: "if expressions with an always-throwing first branch can be refactored to
 ------------------------------
 
 
+test: "if expressions with an always-throwing second branch can be refactored to unless"
+------------------------------
+(define (f c)
+  (if c
+      (displayln "foo")
+      (error 'oops)))
+------------------------------
+------------------------------
+(define (f c)
+  (unless c
+    (error 'oops))
+  (displayln "foo"))
+------------------------------
+
+
 test: "negated if expressions with an always-throwing first branch can be refactored to unless"
 ------------------------------
 (define (f c)
@@ -167,6 +182,21 @@ test: "negated if expressions with an always-throwing first branch can be refact
 ------------------------------
 
 
+test: "negated if expressions with an always-throwing second branch can be refactored to when"
+------------------------------
+(define (f c)
+  (if (not c)
+      (displayln "foo")
+      (error 'oops)))
+------------------------------
+------------------------------
+(define (f c)
+  (when c
+    (error 'oops))
+  (displayln "foo"))
+------------------------------
+
+
 test: "cond expressions with an always-throwing first branch can be refactored to when"
 ------------------------------
 (define (f c)
diff --git a/default-recommendations/conditional-shortcuts.rkt b/default-recommendations/conditional-shortcuts.rkt
index 2b0763d..03350ff 100644
--- a/default-recommendations/conditional-shortcuts.rkt
+++ b/default-recommendations/conditional-shortcuts.rkt
@@ -93,18 +93,31 @@
     conditional.condition conditional.body ...)])
 
 
+(define-syntax-class always-throwing-if-expression
+  #:attributes (equivalent-guard-expression success-expression)
+  #:literals (if)
+  (pattern (if condition:condition-expression
+               fail:always-throwing-expression
+               success-expression)
+    #:with equivalent-guard-expression
+    #'((~if condition.negated? unless when) condition.base-condition fail))
+  (pattern (if condition:condition-expression
+               success-expression
+               fail:always-throwing-expression)
+    #:with equivalent-guard-expression
+    #'((~if condition.negated? when unless) condition.base-condition fail)))
+
+
 (define-refactoring-rule always-throwing-if-to-when
   #:description
   "Using `when` and `unless` is simpler than a conditional with an always-throwing branch."
   #:literals (if)
   [(header:header-form-allowing-internal-definitions
-    (if condition:condition-expression
-        fail:always-throwing-expression
-        else-expression))
+    throwing-if:always-throwing-if-expression)
    (header.formatted
     ...
-    ((~if condition.negated? unless when) condition.base-condition fail)
-    else-expression)])
+    throwing-if.equivalent-guard-expression
+    throwing-if.success-expression)])
 
 
 (define-refactoring-rule always-throwing-cond-to-when