From e730172e47749db8a9d3be5949231bde95343b39 Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Wed, 7 Apr 2021 22:02:45 -0700
Subject: [PATCH] stage2: fix switch validation of handling all enum values

There were several problems, all fixed:
 * AstGen was storing field names as references to the original
   source code bytes. However, that data would be destroyed when the
   source file is updated. Now, it correctly stores the field names in
   the Decl arena for the enum. The same fix applies to error set field
   names.
 * Sema was missing a memset inside `analyzeSwitch`, leaving the "seen
   enum fields" array with undefined memory. Now that they are all
   properly set to null, the validation works.
 * Moved the "enum declared here" note to the end. It looked weird
   interrupting the notes for which enum values were missing.
---
 src/Module.zig      | 35 +++++++++++++++++++++++------------
 src/Sema.zig        | 16 +++++++++-------
 test/stage2/cbe.zig | 15 +++++++++++++++
 3 files changed, 47 insertions(+), 19 deletions(-)

diff --git a/src/Module.zig b/src/Module.zig
index ccf6996cae..933917d948 100644
--- a/src/Module.zig
+++ b/src/Module.zig
@@ -4582,17 +4582,7 @@ pub fn optimizeMode(mod: Module) std.builtin.Mode {
 /// Otherwise, returns a reference to the source code bytes directly.
 /// See also `appendIdentStr` and `parseStrLit`.
 pub fn identifierTokenString(mod: *Module, scope: *Scope, token: ast.TokenIndex) InnerError![]const u8 {
-    return mod.identifierTokenStringTreeArena(scope, token, scope.tree(), scope.arena());
-}
-
-/// `scope` is only used for error reporting.
-pub fn identifierTokenStringTreeArena(
-    mod: *Module,
-    scope: *Scope,
-    token: ast.TokenIndex,
-    tree: *const ast.Tree,
-    arena: *Allocator,
-) InnerError![]const u8 {
+    const tree = scope.tree();
     const token_tags = tree.tokens.items(.tag);
     assert(token_tags[token] == .identifier);
     const ident_name = tree.tokenSlice(token);
@@ -4602,10 +4592,31 @@ pub fn identifierTokenStringTreeArena(
     var buf: ArrayListUnmanaged(u8) = .{};
     defer buf.deinit(mod.gpa);
     try parseStrLit(mod, scope, token, &buf, ident_name, 1);
-    const duped = try arena.dupe(u8, buf.items);
+    const duped = try scope.arena().dupe(u8, buf.items);
     return duped;
 }
 
+/// `scope` is only used for error reporting.
+/// The string is stored in `arena` regardless of whether it uses @"" syntax.
+pub fn identifierTokenStringTreeArena(
+    mod: *Module,
+    scope: *Scope,
+    token: ast.TokenIndex,
+    tree: *const ast.Tree,
+    arena: *Allocator,
+) InnerError![]u8 {
+    const token_tags = tree.tokens.items(.tag);
+    assert(token_tags[token] == .identifier);
+    const ident_name = tree.tokenSlice(token);
+    if (!mem.startsWith(u8, ident_name, "@")) {
+        return arena.dupe(u8, ident_name);
+    }
+    var buf: ArrayListUnmanaged(u8) = .{};
+    defer buf.deinit(mod.gpa);
+    try parseStrLit(mod, scope, token, &buf, ident_name, 1);
+    return arena.dupe(u8, buf.items);
+}
+
 /// Given an identifier token, obtain the string for it (possibly parsing as a string
 /// literal if it is @"" syntax), and append the string to `buf`.
 /// See also `identifierTokenString` and `parseStrLit`.
diff --git a/src/Sema.zig b/src/Sema.zig
index 134e569948..a0be08ed71 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -2789,6 +2789,8 @@ fn analyzeSwitch(
             var seen_fields = try gpa.alloc(?AstGen.SwitchProngSrc, operand.ty.enumFieldCount());
             defer gpa.free(seen_fields);
 
+            mem.set(?AstGen.SwitchProngSrc, seen_fields, null);
+
             var extra_index: usize = special.end;
             {
                 var scalar_i: u32 = 0;
@@ -2849,12 +2851,6 @@ fn analyzeSwitch(
                                 .{},
                             );
                             errdefer msg.destroy(sema.gpa);
-                            try mod.errNoteNonLazy(
-                                operand.ty.declSrcLoc(),
-                                msg,
-                                "enum '{}' declared here",
-                                .{operand.ty},
-                            );
                             for (seen_fields) |seen_src, i| {
                                 if (seen_src != null) continue;
 
@@ -2865,10 +2861,16 @@ fn analyzeSwitch(
                                     &block.base,
                                     src,
                                     msg,
-                                    "unhandled enumeration value: '{s}",
+                                    "unhandled enumeration value: '{s}'",
                                     .{field_name},
                                 );
                             }
+                            try mod.errNoteNonLazy(
+                                operand.ty.declSrcLoc(),
+                                msg,
+                                "enum '{}' declared here",
+                                .{operand.ty},
+                            );
                             break :msg msg;
                         };
                         return mod.failWithOwnedErrorMsg(&block.base, msg);
diff --git a/test/stage2/cbe.zig b/test/stage2/cbe.zig
index b0386f6246..3cf95ab6d6 100644
--- a/test/stage2/cbe.zig
+++ b/test/stage2/cbe.zig
@@ -702,6 +702,21 @@ pub fn addCases(ctx: *TestContext) !void {
             ":3:15: error: enum 'E' has no tag with value 3",
             ":1:11: note: enum declared here",
         });
+
+        case.addError(
+            \\const E = enum { a, b, c };
+            \\export fn foo() void {
+            \\    var x: E = .a;
+            \\    switch (x) {
+            \\        .a => {},
+            \\        .c => {},
+            \\    }
+            \\}
+        , &.{
+            ":4:5: error: switch must handle all possibilities",
+            ":4:5: note: unhandled enumeration value: 'b'",
+            ":1:11: note: enum 'E' declared here",
+        });
     }
 
     ctx.c("empty start function", linux_x64,