fix(es/minifier): Fix inlining of uninitialized variables (#4292)

crates/swc/tests/fixture/issues-4xxx/issue-4276/input/.swcrc

@@ -0,0 +1,68 @@
+{
+    "jsc": {
+        "parser": {
+            "syntax": "ecmascript",
+            "jsx": false
+        },
+        "target": "es2015",
+        "loose": false,
+        "minify": {
+            "compress": {
+                "arguments": false,
+                "arrows": true,
+                "booleans": true,
+                "booleans_as_integers": false,
+                "collapse_vars": true,
+                "comparisons": true,
+                "computed_props": false,
+                "conditionals": false,
+                "dead_code": false,
+                "directives": false,
+                "drop_console": false,
+                "drop_debugger": true,
+                "evaluate": true,
+                "expression": true,
+                "hoist_funs": false,
+                "hoist_props": true,
+                "hoist_vars": false,
+                "if_return": true,
+                "join_vars": true,
+                "keep_classnames": false,
+                "keep_fargs": true,
+                "keep_fnames": false,
+                "keep_infinity": false,
+                "loops": true,
+                "negate_iife": true,
+                "properties": true,
+                "reduce_funcs": false,
+                "reduce_vars": true,
+                "side_effects": true,
+                "switches": false,
+                "typeofs": true,
+                "unsafe": false,
+                "unsafe_arrows": false,
+                "unsafe_comps": false,
+                "unsafe_Function": false,
+                "unsafe_math": false,
+                "unsafe_symbols": false,
+                "unsafe_methods": false,
+                "unsafe_proto": false,
+                "unsafe_regexp": false,
+                "unsafe_undefined": false,
+                "unused": true
+            },
+            "mangle": {
+                "toplevel": true,
+                "keep_classnames": false,
+                "keep_fnames": false,
+                "keep_private_props": false,
+                "ie8": false,
+                "safari10": false
+            }
+        }
+    },
+    "module": {
+        "type": "es6"
+    },
+    "minify": true
+}

crates/swc/tests/fixture/issues-4xxx/issue-4276/input/input.js

@@ -0,0 +1,7 @@
+const foo = 'foo-';
+
+console.log(foo)
+const A = `${foo}bar`;
+const B = `${foo}bar2`;
+
+console.log("test", foo, A, B)

crates/swc/tests/fixture/issues-4xxx/issue-4276/output/input.js

@@ -0,0 +1 @@
+const a="foo-";console.log(a);const b=`${a}bar`,c=`${a}bar2`;console.log("test",a,b,c)

crates/swc_ecma_minifier/src/compress/optimize/strings.rs

@@ -129,13 +129,19 @@ where
                     .data
                     .vars
                     .get(&i.to_id())
-                    .map(|v| v.assign_count == 0 && !v.declared_as_fn_param)
+                    .map(|v| {
+                        v.declared
+                            && !v.var_initialized
+                            && !v.cond_init
+                            && v.assign_count == 0
+                            && !v.declared_as_fn_param
+                    })
                     .unwrap_or(false)
                 {
                     self.changed = true;
                     tracing::debug!(
-                        "strings: Converting a reference ({}{:?}) into `undefined` (in string \
-                         context)",
+                        "strings: Converting an unresolved reference ({}{:?}) into `undefined` \
+                         (in string context)",
                         i.sym,
                         i.span.ctxt
                     );