fix: emit JSON from icp canister logs --json instead of human-readable text

CHANGELOG.md

@@ -7,6 +7,8 @@ bump. Currently experimental: project bundling, project dependencies
 
 # Unreleased
 
+* fix: `icp canister logs` no longer has its output formats swapped. `--json` emitted the human-readable lines and the default emitted JSON; now `--json` emits machine-readable JSON (terminated by a newline) and the default emits the human-readable lines. `--follow` was already correct and is unchanged. Scripts that relied on the inverted behavior — parsing the default output as JSON, or omitting `--json` to get JSON — must now pass `--json`.
+
 # v1.3.0
 
 * feat: a canister environment variable's value can now be read from a file, by writing `var: { path: <file> }` in place of `var: value`. The path resolves against the canister's directory — including in an environment override, matching `init_args` — and surrounding whitespace is trimmed off the file's contents. The file is read when the project is loaded, so a missing file fails before anything is deployed. `icp project bundle` writes the value into the bundled manifest inline, rejecting a file outside the project as it does for other manifest file references.

crates/icp-cli/src/commands/canister/logs.rs

@@ -1,4 +1,4 @@
-use std::io::stdout;
+use std::io::{Write as _, stdout};
 
 use anyhow::{Context as _, anyhow};
 use candid::Principal;
@@ -179,17 +179,9 @@ async fn fetch_and_display_logs(
         .context("Failed to fetch canister logs")?;
 
     if args.json {
-        println!(
-            "{}",
-            result
-                .canister_log_records
-                .iter()
-                .map(format_log)
-                .format("\n")
-        );
-    } else {
+        let mut out = stdout();
         serde_json::to_writer(
-            stdout(),
+            &mut out,
             &JsonListRecord {
                 log_records: result
                     .canister_log_records
@@ -202,6 +194,19 @@ async fn fetch_and_display_logs(
                     .collect(),
             },
         )?;
+        // Unlike the other `--json` sites in this module, terminate the document with a
+        // newline: it is the entirety of stdout, so without it the shell prompt lands
+        // mid-line. Covered by `canister_logs_single_fetch`.
+        writeln!(out)?;
+    } else {
+        println!(
+            "{}",
+            result
+                .canister_log_records
+                .iter()
+                .map(format_log)
+                .format("\n")
+        );
     }
 
     Ok(())

crates/icp-cli/tests/canister_logs_tests.rs

@@ -74,7 +74,8 @@ async fn canister_logs_single_fetch() {
         .assert()
         .success();
 
-    // Fetch logs
+    // Fetch logs: the default emits the human-readable "[idx. timestamp]: content" lines,
+    // not JSON. (Regression: this orientation was once swapped with `--json`.)
     ctx.icp()
         .current_dir(&project_dir)
         .args([
@@ -86,8 +87,45 @@ async fn canister_logs_single_fetch() {
         ])
         .assert()
         .success()
-        .stdout(contains("Test message 1"))
-        .stdout(contains("Test message 2"));
+        .stdout(contains("]: Test message 1"))
+        .stdout(contains("]: Test message 2"))
+        .stdout(contains("log_records").not());
+
+    // With --json: parseable JSON in the JsonListRecord shape, terminated by a newline.
+    let json_stdout = ctx
+        .icp()
+        .current_dir(&project_dir)
+        .args([
+            "canister",
+            "logs",
+            "logger",
+            "--json",
+            "--environment",
+            "random-environment",
+        ])
+        .assert()
+        .success()
+        .get_output()
+        .stdout
+        .clone();
+    let json_stdout = String::from_utf8(json_stdout).expect("stdout is not valid UTF-8");
+    assert!(
+        json_stdout.ends_with('\n'),
+        "--json output should end with a newline, got {json_stdout:?}"
+    );
+    let parsed: serde_json::Value =
+        serde_json::from_str(json_stdout.trim()).expect("--json output should be valid JSON");
+    let records = parsed["log_records"]
+        .as_array()
+        .expect("--json output should contain a log_records array");
+    for message in ["Test message 1", "Test message 2"] {
+        let record = records
+            .iter()
+            .find(|r| r["content"].as_str() == Some(message))
+            .unwrap_or_else(|| panic!("--json output should contain {message:?}"));
+        assert!(record["timestamp"].is_u64());
+        assert!(record["index"].is_u64());
+    }
 }
 
 #[cfg(unix)] // moc