Comments on minimum cli version and on gated logged in fields (#314)

test plan:
make


- [x] I ran `make setup && make` to update the generated code after
editing a `.atd` file (TODO: have a CI check)
- [x] I made sure we're still backward compatible with old versions of
the CLI.
For example, the Semgrep backend need to still be able to *consume* data
generated
	  by Semgrep 1.17.0.
See
https://atd.readthedocs.io/en/latest/atdgen-tutorial.html#smooth-protocol-upgrades

semgrep_output_v1.atd

@@ -1,12 +1,21 @@
 (*****************************************************************************)
 (* Prelude *)
 (*****************************************************************************)
-(* Specification of the Semgrep CLI JSON output format using ATD
+(* Specification of the Semgrep CLI JSON output formats using ATD
  * (see https://atd.readthedocs.io/en/latest/ for more information on ATD).
  *
- * This file specifies the JSON format of the 'semgrep scan --json' command,
- * as well as the JSON format of messages sent to the Semgrep backend by the
- * 'semgrep ci' command, and the format of 'semgrep test --json'.
+ * This file specifies the JSON formats of:
+ *  - the output of the 'semgrep scan --json' command
+ *  - the output of the 'semgrep test --json' command
+ *  - the messages sent (and received) to the Semgrep backend by the
+ *    'semgrep ci' command
+ *
+ * There are other important form of outputs which are not specified here:
+ *  - The semgrep metrics sent to https://metrics.semgrep.dev in
+ *    semgrep_metrics.atd
+ *  - The parsing stats of semgrep-core -parsing_stats -json have its own
+ *    Parsing_stats.atd
+ *  - The schema for the generic AST dump is in AST_generic_v1.atd
  * For the definition of the Semgrep input (the rules), see rule_schema_v2.atd
  *
  * This file has the _v1 suffix to explicitely represent the
@@ -24,10 +33,11 @@
  * should not rely on them as those fields may be changed or removed.
  * They are not part of the "API" of Semgrep.
  *
- * !!Again, keep in mind that this file is used both by the CLI to *produce* a
+ * Again, keep in mind that this file is used both by the CLI to *produce* a
  * JSON output, and by our backends to *consume* the JSON, including to
- * consume the JSON produced by old versions of the CLI. As of Sep 2023,
- * our backend is still supporting as far as Semgrep 1.17.0!!
+ * consume the JSON produced by old versions of the CLI. As of Nov 2024,
+ * our backend is still supporting as far as Semgrep 1.50.0 released Nov 2023.
+ * (see server/semgrep_app/util/cli_version_support.py in the semgrep-app repo)
  *
  *
  * This file is translated in OCaml modules by atdgen. Look for the
@@ -54,13 +64,6 @@
  *    removing gradually the semgrep-core JSON output.
  *  - it was extended to support 'semgrep ci' output to type most messages
  *    sent between the Semgrep CLI and the Semgrep backend
- *
- * There are other important form of outputs which are not specified here:
- *  - The semgrep metrics sent to https://metrics.semgrep.dev in
- *    semgrep_metrics.atd
- *  - The parsing stats of semgrep-core -parsing_stats -json have its own
- *    Parsing_stats.atd
- *  - The schema for the generic AST dump is in AST_generic_v1.atd
  *)
 
 (* escape hatch *)
@@ -70,7 +73,10 @@ type raw_json <ocaml module="Yojson.Basic" t="t"> = abstract
 (* String aliases *)
 (*****************************************************************************)
 
-(* File path. less: could convert directly to Path class of pathlib library for Python *)
+(* File path.
+ * less: could convert directly to Path class of pathlib library for Python
+ * See libs/commons/ATD_string_wrap.ml for more info on those ATD_string_wrap.
+ *)
 type fpath <ocaml attr="deriving show, eq"> <python decorator="dataclass(frozen=True)">= string wrap <ocaml module="ATD_string_wrap.Fpath">
 
 type uri = string wrap <ocaml module="ATD_string_wrap.Uri">
@@ -188,17 +194,19 @@ type pro_feature
     proprietary_language: bool;
 }
 
-(* Report the engine used to detect each finding. Additionally, if we are able to
-   infer that the finding could only be detected using the pro engine, report that
-   the pro engine is required and include basic information about which feature is
-   required.
+(* Report the engine used to detect each finding. Additionally, if we are able
+   to infer that the finding could only be detected using the pro engine,
+   report that the pro engine is required and include basic information about
+   which feature is required.
 
    OSS = ran with OSS
-   PRO = ran with PRO, but we didn't infer that OSS couldn't have found this finding
+   PRO = ran with PRO, but we didn't infer that OSS couldn't have found this
+   finding
    PRO_REQUIRED = ran with PRO and requires a PRO feature (see pro_feature_used)
 
    Note: OSS and PRO could have clearer names, but for backwards compatibility
-   we're leaving them as is *)
+   we're leaving them as is
+*)
 type engine_of_finding
      <ocaml attr="deriving show">
      <python decorator="dataclass(frozen=True)"> = [
@@ -303,7 +311,8 @@ type cli_match = {
 }
 
 type cli_match_extra = {
-  (* TODO: inherit match_extra; but need ?metavars because of dependency_aware code *)
+  (* Since 1.98.0, you need to be logged in to get this field.
+   * note: we also need ?metavars because dependency_aware code *)
   ?metavars: metavars option;
 
   (* Those fields are derived from the rule but the metavariables
@@ -327,7 +336,7 @@ type cli_match_extra = {
   metadata: raw_json;
   severity: match_severity;
 
-  (* added by the CLI (see formatter/json.py) *)
+  (* Since 1.98.0, you need to be logged in to get those fields *)
   fingerprint: string;
   lines: string;
 
@@ -336,14 +345,14 @@ type cli_match_extra = {
   (* EXPERIMENTAL: added by dependency_aware code *)
   ?sca_info: sca_info option;
 
-  (* EXPERIMENTAL: For now, present only for taint findings. May be extended to others
-   * later on. *)
+  (* EXPERIMENTAL: For now, present only for taint findings. May be extended to
+   * otherslater on. *)
   ?dataflow_trace: match_dataflow_trace option;
 
   ?engine_kind: engine_of_finding option;
 
-  (* EXPERIMENTAL: If present indicates the status of postprocessor validation. This
-   * field not being present should be equivalent to No_validator.
+  (* EXPERIMENTAL: If present indicates the status of postprocessor validation.
+   * This field not being present should be equivalent to No_validator.
    * Added in semgrep 1.37.0 *)
   ?validation_state: validation_state option;
   (* EXPERIMENTAL: added by secrets post-processing & historical scanning code
@@ -360,8 +369,6 @@ type cli_match_extra = {
 
 (* Name/value map of the matched metavariables.
  * The leading '$' must be included in the metavariable name.
- * TODO: semgrep-core always return a metavars, but dependency_aware Python code
- * does not always generate a metavars
 *)
 type metavars = (string * metavar_value) list
   <json repr="object">