From 5d4a951bb653bb1a7c8570d28246396eaa3e0713 Mon Sep 17 00:00:00 2001
From: Paul King <paulk@asert.com.au>
Date: Wed, 21 Nov 2018 14:35:36 +1000
Subject: [PATCH] GROOVY-8882: CS: Loop over elements of String has different
 element type (closes #827)

---
 .../transform/sc/StaticCompilationVisitor.java | 11 ++++++++++-
 .../stc/StaticTypeCheckingVisitor.java         | 10 ++++++++--
 .../groovy/transform/stc/LoopsSTCTest.groovy   | 18 ++++++++++++++++++
 3 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/src/main/java/org/codehaus/groovy/transform/sc/StaticCompilationVisitor.java b/src/main/java/org/codehaus/groovy/transform/sc/StaticCompilationVisitor.java
index f66b24a04c9..036dbe54d38 100644
--- a/src/main/java/org/codehaus/groovy/transform/sc/StaticCompilationVisitor.java
+++ b/src/main/java/org/codehaus/groovy/transform/sc/StaticCompilationVisitor.java
@@ -72,6 +72,8 @@
 import java.util.Map;
 import java.util.Set;
 
+import static org.codehaus.groovy.ast.ClassHelper.Character_TYPE;
+import static org.codehaus.groovy.ast.ClassHelper.STRING_TYPE;
 import static org.codehaus.groovy.ast.tools.GenericsUtils.addMethodGenerics;
 import static org.codehaus.groovy.ast.tools.GenericsUtils.applyGenericsContextToPlaceHolders;
 import static org.codehaus.groovy.ast.tools.GenericsUtils.correctToGenericsSpecRecurse;
@@ -440,7 +442,14 @@ public void visitForLoop(final ForStatement forLoop) {
         Expression collectionExpression = forLoop.getCollectionExpression();
         if (!(collectionExpression instanceof ClosureListExpression)) {
             final ClassNode collectionType = getType(forLoop.getCollectionExpression());
-            ClassNode componentType = inferLoopElementType(collectionType);
+            ClassNode forLoopVariableType = forLoop.getVariableType();
+            ClassNode componentType;
+            if (Character_TYPE.equals(ClassHelper.getWrapper(forLoopVariableType)) && STRING_TYPE.equals(collectionType)) {
+                // we allow auto-coercion here
+                componentType = forLoopVariableType;
+            } else {
+                componentType = inferLoopElementType(collectionType);
+            }
             forLoop.getVariable().setType(componentType);
             forLoop.getVariable().setOriginType(componentType);
         }
diff --git a/src/main/java/org/codehaus/groovy/transform/stc/StaticTypeCheckingVisitor.java b/src/main/java/org/codehaus/groovy/transform/stc/StaticTypeCheckingVisitor.java
index de2abff5a64..12a48d3f864 100644
--- a/src/main/java/org/codehaus/groovy/transform/stc/StaticTypeCheckingVisitor.java
+++ b/src/main/java/org/codehaus/groovy/transform/stc/StaticTypeCheckingVisitor.java
@@ -1886,8 +1886,14 @@ public void visitForLoop(final ForStatement forLoop) {
         } else {
             collectionExpression.visit(this);
             final ClassNode collectionType = getType(collectionExpression);
-            ClassNode componentType = inferLoopElementType(collectionType);
             ClassNode forLoopVariableType = forLoop.getVariableType();
+            ClassNode componentType;
+            if (Character_TYPE.equals(ClassHelper.getWrapper(forLoopVariableType)) && STRING_TYPE.equals(collectionType)) {
+                // we allow auto-coercion here
+                componentType = forLoopVariableType;
+            } else {
+                componentType = inferLoopElementType(collectionType);
+            }
             if (ClassHelper.getUnwrapper(componentType) == forLoopVariableType) {
                 // prefer primitive type over boxed type
                 componentType = forLoopVariableType;
@@ -1931,7 +1937,7 @@ public static ClassNode inferLoopElementType(final ClassNode collectionType) {
                 componentType = MAP_ENTRY_TYPE.getPlainNodeReference();
                 componentType.setGenericsTypes(genericsTypes);
             } else if (STRING_TYPE.equals(collectionType)) {
-                componentType = ClassHelper.Character_TYPE;
+                componentType = ClassHelper.STRING_TYPE;
             } else if (ENUMERATION_TYPE.equals(collectionType)) {
                 // GROOVY-6123
                 ClassNode intf = GenericsUtils.parameterizeType(collectionType, ENUMERATION_TYPE);
diff --git a/src/test/groovy/transform/stc/LoopsSTCTest.groovy b/src/test/groovy/transform/stc/LoopsSTCTest.groovy
index cdb07abaace..0bf2e1fdc86 100644
--- a/src/test/groovy/transform/stc/LoopsSTCTest.groovy
+++ b/src/test/groovy/transform/stc/LoopsSTCTest.groovy
@@ -18,6 +18,8 @@
  */
 package groovy.transform.stc
 
+import groovy.transform.CompileStatic
+
 /**
  * Unit tests for static type checking : loops.
  *
@@ -45,6 +47,22 @@ class LoopsSTCTest extends StaticTypeCheckingTestCase {
         '''
     }
 
+    // GROOVY-8882
+    void testStringCollectionLoop() {
+        for (char c in 'abc') assert c instanceof Character
+        for (Character c in 'abc') assert c instanceof Character
+        for (String s in 'abc') assert s instanceof String
+        for (s in 'abc') assert s instanceof String
+    }
+
+    // GROOVY-8882
+    @CompileStatic
+    void testStringCollectionLoopCS() {
+        for (char c in 'abc') assert c instanceof Character
+        for (Character c in 'abc') assert c instanceof Character
+        for (String s in 'abc') assert s instanceof String
+        for (s in 'abc') assert s instanceof String
+    }
 
     void testMethodCallWithEachAndDefAndTwoFooMethods() {
         shouldFailWithMessages '''