stage2: dbg_stmt ZIR instructions have line/col

instead of node indexes.

 * AstGen: dbg_stmt instructions now have line and column indexes,
   relative to the parent declaration. This allows codegen to emit debug
   info without having the source bytes, tokens, or AST nodes loaded
   in memory.
 * ZIR: each decl has the absolute line number. This allows computing
   line numbers from offsets without consulting source code bytes.

Memory management: creating a function definition does not prematurely
set the Decl arena. Instead the function is allocated with the general
purpose allocator.

Codegen no longer looks at source code bytes for any reason. They can
remain unloaded from disk.

1 files changed, 61 insertions, 12 deletions

diff --git a/src/AstGen.zig b/src/AstGen.zig
index 1c75a12069..b5b31c4095 100644
--- a/src/AstGen.zig
+++ b/src/AstGen.zig
@@ -94,6 +94,7 @@ pub fn generate(gpa: *Allocator, file: *Scope.File) InnerError!Zir {
         .force_comptime = true,
         .parent = &file.base,
         .decl_node_index = 0,
+        .decl_line = 0,
         .astgen = &astgen,
     };
     defer gen_scope.instructions.deinit(gpa);
@@ -2056,7 +2057,7 @@ fn unusedResultExpr(gz: *GenZir, scope: *Scope, statement: ast.Node.Index) Inner
             // ZIR instructions that are always either `noreturn` or `void`.
             .breakpoint,
             .fence,
-            .dbg_stmt_node,
+            .dbg_stmt,
             .ensure_result_used,
             .ensure_result_non_error,
             .@"export",
@@ -2395,9 +2396,25 @@ fn varDecl(
 }
 
 fn emitDbgNode(gz: *GenZir, node: ast.Node.Index) !void {
-    if (!gz.force_comptime) {
-        _ = try gz.addNode(.dbg_stmt_node, node);
-    }
+    // The instruction emitted here is for debugging runtime code.
+    // If the current block will be evaluated only during semantic analysis
+    // then no dbg_stmt ZIR instruction is needed.
+    if (gz.force_comptime) return;
+
+    const astgen = gz.astgen;
+    const tree = &astgen.file.tree;
+    const node_tags = tree.nodes.items(.tag);
+    const token_starts = tree.tokens.items(.start);
+    const decl_start = token_starts[tree.firstToken(gz.decl_node_index)];
+    const node_start = token_starts[tree.firstToken(node)];
+    const source = tree.source[decl_start..node_start];
+    const loc = std.zig.findLineColumn(source, source.len);
+    _ = try gz.add(.{ .tag = .dbg_stmt, .data = .{
+        .dbg_stmt = .{
+            .line = @intCast(u32, loc.line),
+            .column = @intCast(u32, loc.column),
+        },
+    } });
 }
 
 fn assign(gz: *GenZir, scope: *Scope, infix_node: ast.Node.Index) InnerError!void {
@@ -2689,6 +2706,7 @@ fn fnDecl(
     var decl_gz: GenZir = .{
         .force_comptime = true,
         .decl_node_index = fn_proto.ast.proto_node,
+        .decl_line = gz.calcLine(decl_node),
         .parent = &gz.base,
         .astgen = astgen,
     };
@@ -2791,7 +2809,7 @@ fn fnDecl(
             return astgen.failTok(maybe_bang, "function prototype may not have inferred error set", .{});
         }
         break :func try decl_gz.addFunc(.{
-            .src_node = fn_proto.ast.proto_node,
+            .src_node = decl_node,
             .ret_ty = return_type_inst,
             .param_types = param_types,
             .body = &[0]Zir.Inst.Index{},
@@ -2810,6 +2828,7 @@ fn fnDecl(
         var fn_gz: GenZir = .{
             .force_comptime = false,
             .decl_node_index = fn_proto.ast.proto_node,
+            .decl_line = decl_gz.decl_line,
             .parent = &decl_gz.base,
             .astgen = astgen,
         };
@@ -2866,7 +2885,7 @@ fn fnDecl(
         astgen.fn_block = prev_fn_block;
 
         break :func try decl_gz.addFunc(.{
-            .src_node = fn_proto.ast.proto_node,
+            .src_node = decl_node,
             .ret_ty = return_type_inst,
             .param_types = param_types,
             .body = fn_gz.instructions.items,
@@ -2889,12 +2908,16 @@ fn fnDecl(
     _ = try decl_gz.addBreak(.break_inline, block_inst, func_inst);
     try decl_gz.setBlockBody(block_inst);
 
-    try wip_decls.payload.ensureUnusedCapacity(gpa, 8);
+    try wip_decls.payload.ensureUnusedCapacity(gpa, 9);
     {
         const contents_hash = std.zig.hashSrc(tree.getNodeSource(decl_node));
         const casted = @bitCast([4]u32, contents_hash);
         wip_decls.payload.appendSliceAssumeCapacity(&casted);
     }
+    {
+        const line_delta = decl_gz.decl_line - gz.decl_line;
+        wip_decls.payload.appendAssumeCapacity(line_delta);
+    }
     wip_decls.payload.appendAssumeCapacity(fn_name_str_index);
     wip_decls.payload.appendAssumeCapacity(block_inst);
     if (align_inst != .none) {
@@ -2925,6 +2948,7 @@ fn globalVarDecl(
     var block_scope: GenZir = .{
         .parent = scope,
         .decl_node_index = node,
+        .decl_line = gz.calcLine(node),
         .astgen = astgen,
         .force_comptime = true,
     };
@@ -3024,12 +3048,16 @@ fn globalVarDecl(
     const name_token = var_decl.ast.mut_token + 1;
     const name_str_index = try astgen.identAsString(name_token);
 
-    try wip_decls.payload.ensureUnusedCapacity(gpa, 8);
+    try wip_decls.payload.ensureUnusedCapacity(gpa, 9);
     {
         const contents_hash = std.zig.hashSrc(tree.getNodeSource(node));
         const casted = @bitCast([4]u32, contents_hash);
         wip_decls.payload.appendSliceAssumeCapacity(&casted);
     }
+    {
+        const line_delta = block_scope.decl_line - gz.decl_line;
+        wip_decls.payload.appendAssumeCapacity(line_delta);
+    }
     wip_decls.payload.appendAssumeCapacity(name_str_index);
     wip_decls.payload.appendAssumeCapacity(block_inst);
     if (align_inst != .none) {
@@ -3060,6 +3088,7 @@ fn comptimeDecl(
     var decl_block: GenZir = .{
         .force_comptime = true,
         .decl_node_index = node,
+        .decl_line = gz.calcLine(node),
         .parent = scope,
         .astgen = astgen,
     };
@@ -3071,12 +3100,16 @@ fn comptimeDecl(
     }
     try decl_block.setBlockBody(block_inst);
 
-    try wip_decls.payload.ensureUnusedCapacity(gpa, 6);
+    try wip_decls.payload.ensureUnusedCapacity(gpa, 7);
     {
         const contents_hash = std.zig.hashSrc(tree.getNodeSource(node));
         const casted = @bitCast([4]u32, contents_hash);
         wip_decls.payload.appendSliceAssumeCapacity(&casted);
     }
+    {
+        const line_delta = decl_block.decl_line - gz.decl_line;
+        wip_decls.payload.appendAssumeCapacity(line_delta);
+    }
     wip_decls.payload.appendAssumeCapacity(0);
     wip_decls.payload.appendAssumeCapacity(block_inst);
 }
@@ -3107,6 +3140,7 @@ fn usingnamespaceDecl(
     var decl_block: GenZir = .{
         .force_comptime = true,
         .decl_node_index = node,
+        .decl_line = gz.calcLine(node),
         .parent = scope,
         .astgen = astgen,
     };
@@ -3116,12 +3150,16 @@ fn usingnamespaceDecl(
     _ = try decl_block.addBreak(.break_inline, block_inst, namespace_inst);
     try decl_block.setBlockBody(block_inst);
 
-    try wip_decls.payload.ensureUnusedCapacity(gpa, 6);
+    try wip_decls.payload.ensureUnusedCapacity(gpa, 7);
     {
         const contents_hash = std.zig.hashSrc(tree.getNodeSource(node));
         const casted = @bitCast([4]u32, contents_hash);
         wip_decls.payload.appendSliceAssumeCapacity(&casted);
     }
+    {
+        const line_delta = decl_block.decl_line - gz.decl_line;
+        wip_decls.payload.appendAssumeCapacity(line_delta);
+    }
     wip_decls.payload.appendAssumeCapacity(0);
     wip_decls.payload.appendAssumeCapacity(block_inst);
 }
@@ -3147,6 +3185,7 @@ fn testDecl(
     var decl_block: GenZir = .{
         .force_comptime = true,
         .decl_node_index = node,
+        .decl_line = gz.calcLine(node),
         .parent = scope,
         .astgen = astgen,
     };
@@ -3167,6 +3206,7 @@ fn testDecl(
     var fn_block: GenZir = .{
         .force_comptime = false,
         .decl_node_index = node,
+        .decl_line = decl_block.decl_line,
         .parent = &decl_block.base,
         .astgen = astgen,
     };
@@ -3200,12 +3240,16 @@ fn testDecl(
     _ = try decl_block.addBreak(.break_inline, block_inst, func_inst);
     try decl_block.setBlockBody(block_inst);
 
-    try wip_decls.payload.ensureUnusedCapacity(gpa, 6);
+    try wip_decls.payload.ensureUnusedCapacity(gpa, 7);
     {
         const contents_hash = std.zig.hashSrc(tree.getNodeSource(node));
         const casted = @bitCast([4]u32, contents_hash);
         wip_decls.payload.appendSliceAssumeCapacity(&casted);
     }
+    {
+        const line_delta = decl_block.decl_line - gz.decl_line;
+        wip_decls.payload.appendAssumeCapacity(line_delta);
+    }
     wip_decls.payload.appendAssumeCapacity(test_name);
     wip_decls.payload.appendAssumeCapacity(block_inst);
 }
@@ -3237,6 +3281,7 @@ fn structDeclInner(
     var block_scope: GenZir = .{
         .parent = scope,
         .decl_node_index = node,
+        .decl_line = gz.calcLine(node),
         .astgen = astgen,
         .force_comptime = true,
         .ref_start_index = gz.ref_start_index,
@@ -3448,6 +3493,7 @@ fn unionDeclInner(
     var block_scope: GenZir = .{
         .parent = scope,
         .decl_node_index = node,
+        .decl_line = gz.calcLine(node),
         .astgen = astgen,
         .force_comptime = true,
         .ref_start_index = gz.ref_start_index,
@@ -3797,6 +3843,7 @@ fn containerDecl(
             var block_scope: GenZir = .{
                 .parent = scope,
                 .decl_node_index = node,
+                .decl_line = gz.calcLine(node),
                 .astgen = astgen,
                 .force_comptime = true,
                 .ref_start_index = gz.ref_start_index,
@@ -4464,7 +4511,9 @@ fn boolBinOp(
     node: ast.Node.Index,
     zir_tag: Zir.Inst.Tag,
 ) InnerError!Zir.Inst.Ref {
-    const node_datas = gz.tree().nodes.items(.data);
+    const astgen = gz.astgen;
+    const tree = &astgen.file.tree;
+    const node_datas = tree.nodes.items(.data);
 
     const lhs = try expr(gz, scope, bool_rl, node_datas[node].lhs);
     const bool_br = try gz.addBoolBr(zir_tag, lhs);